* [PATCH v4 0/2] tiocsti-restrict : make TIOCSTI ioctl require CAP_SYS_ADMIN
@ 2017-04-24 5:15 ` Matt Brown
0 siblings, 0 replies; 33+ messages in thread
From: Matt Brown @ 2017-04-24 5:15 UTC (permalink / raw)
To: serge, jmorris, gregkh, jslaby, corbet, keescook
Cc: akpm, jannh, kernel-hardening, linux-security-module,
linux-kernel, linux-doc
This patchset introduces the tiocsti_restrict sysctl, whose default is
controlled via CONFIG_SECURITY_TIOCSTI_RESTRICT. When activated, this
control restricts all TIOCSTI ioctl calls from non CAP_SYS_ADMIN users.
This patch was inspired from GRKERNSEC_HARDEN_TTY.
This patch would have prevented
https://bugzilla.redhat.com/show_bug.cgi?id=1411256 under the following
conditions:
* non-privileged container
* container run inside new user namespace
Possible effects on userland:
There could be a few user programs that would be effected by this
change.
See: <https://codesearch.debian.net/search?q=ioctl%5C%28.*TIOCSTI>
notable programs are: agetty, csh, xemacs and tcsh
However, I still believe that this change is worth it given that the
Kconfig defaults to n. This will be a feature that is turned on for the
same reason that people activate it when using grsecurity. Users of this
opt-in feature will realize that they are choosing security over some OS
features like unprivileged TIOCSTI ioctls, as should be clear in the
Kconfig help message.
Threat Model/Patch Rational:
>From grsecurity's config for GRKERNSEC_HARDEN_TTY.
| There are very few legitimate uses for this functionality and it
| has made vulnerabilities in several 'su'-like programs possible in
| the past. Even without these vulnerabilities, it provides an
| attacker with an easy mechanism to move laterally among other
| processes within the same user's compromised session.
So if one process within a tty session becomes compromised it can follow
that additional processes, that are thought to be in different security
boundaries, can be compromised as a result. When using a program like su
or sudo, these additional processes could be in a tty session where TTY file
descriptors are indeed shared over privilege boundaries.
This is also an excellent writeup about the issue:
<http://www.halfdog.net/Security/2012/TtyPushbackPrivilegeEscalation/>
When user namespaces are in use, the check for the capability
CAP_SYS_ADMIN is done against the user namespace that originally opened
the tty.
# Changes since v3:
* use get_user_ns and put_user_ns to take and drop references to the owner
user namespace because CONFIG_USER_NS is an option
# Changes since v2:
* take/drop reference to user namespace on tty struct alloc/free to prevent
use-after-free.
# Changes since v1:
* added owner_user_ns to tty_struct to enable capability checks against
the namespace that created the tty.
* rewording in different places to make patchset purpose clear
* Added Documentation
^ permalink raw reply [flat|nested] 33+ messages in thread
* [kernel-hardening] [PATCH v4 0/2] tiocsti-restrict : make TIOCSTI ioctl require CAP_SYS_ADMIN @ 2017-04-24 5:15 ` Matt Brown 0 siblings, 0 replies; 33+ messages in thread From: Matt Brown @ 2017-04-24 5:15 UTC (permalink / raw) To: serge, jmorris, gregkh, jslaby, corbet, keescook Cc: akpm, jannh, kernel-hardening, linux-security-module, linux-kernel, linux-doc This patchset introduces the tiocsti_restrict sysctl, whose default is controlled via CONFIG_SECURITY_TIOCSTI_RESTRICT. When activated, this control restricts all TIOCSTI ioctl calls from non CAP_SYS_ADMIN users. This patch was inspired from GRKERNSEC_HARDEN_TTY. This patch would have prevented https://bugzilla.redhat.com/show_bug.cgi?id=1411256 under the following conditions: * non-privileged container * container run inside new user namespace Possible effects on userland: There could be a few user programs that would be effected by this change. See: <https://codesearch.debian.net/search?q=ioctl%5C%28.*TIOCSTI> notable programs are: agetty, csh, xemacs and tcsh However, I still believe that this change is worth it given that the Kconfig defaults to n. This will be a feature that is turned on for the same reason that people activate it when using grsecurity. Users of this opt-in feature will realize that they are choosing security over some OS features like unprivileged TIOCSTI ioctls, as should be clear in the Kconfig help message. Threat Model/Patch Rational: >From grsecurity's config for GRKERNSEC_HARDEN_TTY. | There are very few legitimate uses for this functionality and it | has made vulnerabilities in several 'su'-like programs possible in | the past. Even without these vulnerabilities, it provides an | attacker with an easy mechanism to move laterally among other | processes within the same user's compromised session. So if one process within a tty session becomes compromised it can follow that additional processes, that are thought to be in different security boundaries, can be compromised as a result. When using a program like su or sudo, these additional processes could be in a tty session where TTY file descriptors are indeed shared over privilege boundaries. This is also an excellent writeup about the issue: <http://www.halfdog.net/Security/2012/TtyPushbackPrivilegeEscalation/> When user namespaces are in use, the check for the capability CAP_SYS_ADMIN is done against the user namespace that originally opened the tty. # Changes since v3: * use get_user_ns and put_user_ns to take and drop references to the owner user namespace because CONFIG_USER_NS is an option # Changes since v2: * take/drop reference to user namespace on tty struct alloc/free to prevent use-after-free. # Changes since v1: * added owner_user_ns to tty_struct to enable capability checks against the namespace that created the tty. * rewording in different places to make patchset purpose clear * Added Documentation ^ permalink raw reply [flat|nested] 33+ messages in thread
* [PATCH v4 0/2] tiocsti-restrict : make TIOCSTI ioctl require CAP_SYS_ADMIN @ 2017-04-24 5:15 ` Matt Brown 0 siblings, 0 replies; 33+ messages in thread From: Matt Brown @ 2017-04-24 5:15 UTC (permalink / raw) To: linux-security-module This patchset introduces the tiocsti_restrict sysctl, whose default is controlled via CONFIG_SECURITY_TIOCSTI_RESTRICT. When activated, this control restricts all TIOCSTI ioctl calls from non CAP_SYS_ADMIN users. This patch was inspired from GRKERNSEC_HARDEN_TTY. This patch would have prevented https://bugzilla.redhat.com/show_bug.cgi?id=1411256 under the following conditions: * non-privileged container * container run inside new user namespace Possible effects on userland: There could be a few user programs that would be effected by this change. See: <https://codesearch.debian.net/search?q=ioctl%5C%28.*TIOCSTI> notable programs are: agetty, csh, xemacs and tcsh However, I still believe that this change is worth it given that the Kconfig defaults to n. This will be a feature that is turned on for the same reason that people activate it when using grsecurity. Users of this opt-in feature will realize that they are choosing security over some OS features like unprivileged TIOCSTI ioctls, as should be clear in the Kconfig help message. Threat Model/Patch Rational: >From grsecurity's config for GRKERNSEC_HARDEN_TTY. | There are very few legitimate uses for this functionality and it | has made vulnerabilities in several 'su'-like programs possible in | the past. Even without these vulnerabilities, it provides an | attacker with an easy mechanism to move laterally among other | processes within the same user's compromised session. So if one process within a tty session becomes compromised it can follow that additional processes, that are thought to be in different security boundaries, can be compromised as a result. When using a program like su or sudo, these additional processes could be in a tty session where TTY file descriptors are indeed shared over privilege boundaries. This is also an excellent writeup about the issue: <http://www.halfdog.net/Security/2012/TtyPushbackPrivilegeEscalation/> When user namespaces are in use, the check for the capability CAP_SYS_ADMIN is done against the user namespace that originally opened the tty. # Changes since v3: * use get_user_ns and put_user_ns to take and drop references to the owner user namespace because CONFIG_USER_NS is an option # Changes since v2: * take/drop reference to user namespace on tty struct alloc/free to prevent use-after-free. # Changes since v1: * added owner_user_ns to tty_struct to enable capability checks against the namespace that created the tty. * rewording in different places to make patchset purpose clear * Added Documentation -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 33+ messages in thread
* [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct 2017-04-24 5:15 ` Matt Brown (?) @ 2017-04-24 5:15 ` Matt Brown -1 siblings, 0 replies; 33+ messages in thread From: Matt Brown @ 2017-04-24 5:15 UTC (permalink / raw) To: serge, jmorris, gregkh, jslaby, corbet, keescook Cc: akpm, jannh, kernel-hardening, linux-security-module, linux-kernel, linux-doc, Matt Brown This patch adds struct user_namespace *owner_user_ns to the tty_struct. Then it is set to current_user_ns() in the alloc_tty_struct function. This is done to facilitate capability checks against the original user namespace that allocated the tty. E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) This combined with the use of user namespace's will allow hardening protections to be built to mitigate container escapes that utilize TTY ioctls such as TIOCSTI. See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 Signed-off-by: Matt Brown <matt@nmatt.com> --- drivers/tty/tty_io.c | 2 ++ include/linux/tty.h | 2 ++ 2 files changed, 4 insertions(+) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index e6d1a65..c276814 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -171,6 +171,7 @@ static void free_tty_struct(struct tty_struct *tty) put_device(tty->dev); kfree(tty->write_buf); tty->magic = 0xDEADDEAD; + put_user_ns(tty->owner_user_ns); kfree(tty); } @@ -3191,6 +3192,7 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx) tty->index = idx; tty_line_name(driver, idx, tty->name); tty->dev = tty_get_device(tty); + tty->owner_user_ns = get_user_ns(current_user_ns()); return tty; } diff --git a/include/linux/tty.h b/include/linux/tty.h index 1017e904..d902d42 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -12,6 +12,7 @@ #include <uapi/linux/tty.h> #include <linux/rwsem.h> #include <linux/llist.h> +#include <linux/user_namespace.h> /* @@ -333,6 +334,7 @@ struct tty_struct { /* If the tty has a pending do_SAK, queue it here - akpm */ struct work_struct SAK_work; struct tty_port *port; + struct user_namespace *owner_user_ns; }; /* Each of a tty's open files has private_data pointing to tty_file_private */ -- 2.10.2 ^ permalink raw reply related [flat|nested] 33+ messages in thread
* [kernel-hardening] [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct @ 2017-04-24 5:15 ` Matt Brown 0 siblings, 0 replies; 33+ messages in thread From: Matt Brown @ 2017-04-24 5:15 UTC (permalink / raw) To: serge, jmorris, gregkh, jslaby, corbet, keescook Cc: akpm, jannh, kernel-hardening, linux-security-module, linux-kernel, linux-doc, Matt Brown This patch adds struct user_namespace *owner_user_ns to the tty_struct. Then it is set to current_user_ns() in the alloc_tty_struct function. This is done to facilitate capability checks against the original user namespace that allocated the tty. E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) This combined with the use of user namespace's will allow hardening protections to be built to mitigate container escapes that utilize TTY ioctls such as TIOCSTI. See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 Signed-off-by: Matt Brown <matt@nmatt.com> --- drivers/tty/tty_io.c | 2 ++ include/linux/tty.h | 2 ++ 2 files changed, 4 insertions(+) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index e6d1a65..c276814 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -171,6 +171,7 @@ static void free_tty_struct(struct tty_struct *tty) put_device(tty->dev); kfree(tty->write_buf); tty->magic = 0xDEADDEAD; + put_user_ns(tty->owner_user_ns); kfree(tty); } @@ -3191,6 +3192,7 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx) tty->index = idx; tty_line_name(driver, idx, tty->name); tty->dev = tty_get_device(tty); + tty->owner_user_ns = get_user_ns(current_user_ns()); return tty; } diff --git a/include/linux/tty.h b/include/linux/tty.h index 1017e904..d902d42 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -12,6 +12,7 @@ #include <uapi/linux/tty.h> #include <linux/rwsem.h> #include <linux/llist.h> +#include <linux/user_namespace.h> /* @@ -333,6 +334,7 @@ struct tty_struct { /* If the tty has a pending do_SAK, queue it here - akpm */ struct work_struct SAK_work; struct tty_port *port; + struct user_namespace *owner_user_ns; }; /* Each of a tty's open files has private_data pointing to tty_file_private */ -- 2.10.2 ^ permalink raw reply related [flat|nested] 33+ messages in thread
* [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct @ 2017-04-24 5:15 ` Matt Brown 0 siblings, 0 replies; 33+ messages in thread From: Matt Brown @ 2017-04-24 5:15 UTC (permalink / raw) To: linux-security-module This patch adds struct user_namespace *owner_user_ns to the tty_struct. Then it is set to current_user_ns() in the alloc_tty_struct function. This is done to facilitate capability checks against the original user namespace that allocated the tty. E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) This combined with the use of user namespace's will allow hardening protections to be built to mitigate container escapes that utilize TTY ioctls such as TIOCSTI. See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 Signed-off-by: Matt Brown <matt@nmatt.com> --- drivers/tty/tty_io.c | 2 ++ include/linux/tty.h | 2 ++ 2 files changed, 4 insertions(+) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index e6d1a65..c276814 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -171,6 +171,7 @@ static void free_tty_struct(struct tty_struct *tty) put_device(tty->dev); kfree(tty->write_buf); tty->magic = 0xDEADDEAD; + put_user_ns(tty->owner_user_ns); kfree(tty); } @@ -3191,6 +3192,7 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx) tty->index = idx; tty_line_name(driver, idx, tty->name); tty->dev = tty_get_device(tty); + tty->owner_user_ns = get_user_ns(current_user_ns()); return tty; } diff --git a/include/linux/tty.h b/include/linux/tty.h index 1017e904..d902d42 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -12,6 +12,7 @@ #include <uapi/linux/tty.h> #include <linux/rwsem.h> #include <linux/llist.h> +#include <linux/user_namespace.h> /* @@ -333,6 +334,7 @@ struct tty_struct { /* If the tty has a pending do_SAK, queue it here - akpm */ struct work_struct SAK_work; struct tty_port *port; + struct user_namespace *owner_user_ns; }; /* Each of a tty's open files has private_data pointing to tty_file_private */ -- 2.10.2 -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply related [flat|nested] 33+ messages in thread
* Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct 2017-04-24 5:15 ` Matt Brown (?) @ 2017-04-24 13:57 ` Serge E. Hallyn -1 siblings, 0 replies; 33+ messages in thread From: Serge E. Hallyn @ 2017-04-24 13:57 UTC (permalink / raw) To: Matt Brown Cc: serge, jmorris, gregkh, jslaby, corbet, keescook, akpm, jannh, kernel-hardening, linux-security-module, linux-kernel, linux-doc Quoting Matt Brown (matt@nmatt.com): > This patch adds struct user_namespace *owner_user_ns to the tty_struct. > Then it is set to current_user_ns() in the alloc_tty_struct function. > > This is done to facilitate capability checks against the original user > namespace that allocated the tty. > > E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) > > This combined with the use of user namespace's will allow hardening > protections to be built to mitigate container escapes that utilize TTY > ioctls such as TIOCSTI. > > See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 > > Signed-off-by: Matt Brown <matt@nmatt.com> Acked-by: Serge Hallyn <serge@hallyn.com> > --- > drivers/tty/tty_io.c | 2 ++ > include/linux/tty.h | 2 ++ > 2 files changed, 4 insertions(+) > > diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c > index e6d1a65..c276814 100644 > --- a/drivers/tty/tty_io.c > +++ b/drivers/tty/tty_io.c > @@ -171,6 +171,7 @@ static void free_tty_struct(struct tty_struct *tty) > put_device(tty->dev); > kfree(tty->write_buf); > tty->magic = 0xDEADDEAD; > + put_user_ns(tty->owner_user_ns); > kfree(tty); > } > > @@ -3191,6 +3192,7 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx) > tty->index = idx; > tty_line_name(driver, idx, tty->name); > tty->dev = tty_get_device(tty); > + tty->owner_user_ns = get_user_ns(current_user_ns()); > > return tty; > } > diff --git a/include/linux/tty.h b/include/linux/tty.h > index 1017e904..d902d42 100644 > --- a/include/linux/tty.h > +++ b/include/linux/tty.h > @@ -12,6 +12,7 @@ > #include <uapi/linux/tty.h> > #include <linux/rwsem.h> > #include <linux/llist.h> > +#include <linux/user_namespace.h> > > > /* > @@ -333,6 +334,7 @@ struct tty_struct { > /* If the tty has a pending do_SAK, queue it here - akpm */ > struct work_struct SAK_work; > struct tty_port *port; > + struct user_namespace *owner_user_ns; > }; > > /* Each of a tty's open files has private_data pointing to tty_file_private */ > -- > 2.10.2 ^ permalink raw reply [flat|nested] 33+ messages in thread
* [kernel-hardening] Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct @ 2017-04-24 13:57 ` Serge E. Hallyn 0 siblings, 0 replies; 33+ messages in thread From: Serge E. Hallyn @ 2017-04-24 13:57 UTC (permalink / raw) To: Matt Brown Cc: serge, jmorris, gregkh, jslaby, corbet, keescook, akpm, jannh, kernel-hardening, linux-security-module, linux-kernel, linux-doc Quoting Matt Brown (matt@nmatt.com): > This patch adds struct user_namespace *owner_user_ns to the tty_struct. > Then it is set to current_user_ns() in the alloc_tty_struct function. > > This is done to facilitate capability checks against the original user > namespace that allocated the tty. > > E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) > > This combined with the use of user namespace's will allow hardening > protections to be built to mitigate container escapes that utilize TTY > ioctls such as TIOCSTI. > > See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 > > Signed-off-by: Matt Brown <matt@nmatt.com> Acked-by: Serge Hallyn <serge@hallyn.com> > --- > drivers/tty/tty_io.c | 2 ++ > include/linux/tty.h | 2 ++ > 2 files changed, 4 insertions(+) > > diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c > index e6d1a65..c276814 100644 > --- a/drivers/tty/tty_io.c > +++ b/drivers/tty/tty_io.c > @@ -171,6 +171,7 @@ static void free_tty_struct(struct tty_struct *tty) > put_device(tty->dev); > kfree(tty->write_buf); > tty->magic = 0xDEADDEAD; > + put_user_ns(tty->owner_user_ns); > kfree(tty); > } > > @@ -3191,6 +3192,7 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx) > tty->index = idx; > tty_line_name(driver, idx, tty->name); > tty->dev = tty_get_device(tty); > + tty->owner_user_ns = get_user_ns(current_user_ns()); > > return tty; > } > diff --git a/include/linux/tty.h b/include/linux/tty.h > index 1017e904..d902d42 100644 > --- a/include/linux/tty.h > +++ b/include/linux/tty.h > @@ -12,6 +12,7 @@ > #include <uapi/linux/tty.h> > #include <linux/rwsem.h> > #include <linux/llist.h> > +#include <linux/user_namespace.h> > > > /* > @@ -333,6 +334,7 @@ struct tty_struct { > /* If the tty has a pending do_SAK, queue it here - akpm */ > struct work_struct SAK_work; > struct tty_port *port; > + struct user_namespace *owner_user_ns; > }; > > /* Each of a tty's open files has private_data pointing to tty_file_private */ > -- > 2.10.2 ^ permalink raw reply [flat|nested] 33+ messages in thread
* [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct @ 2017-04-24 13:57 ` Serge E. Hallyn 0 siblings, 0 replies; 33+ messages in thread From: Serge E. Hallyn @ 2017-04-24 13:57 UTC (permalink / raw) To: linux-security-module Quoting Matt Brown (matt at nmatt.com): > This patch adds struct user_namespace *owner_user_ns to the tty_struct. > Then it is set to current_user_ns() in the alloc_tty_struct function. > > This is done to facilitate capability checks against the original user > namespace that allocated the tty. > > E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) > > This combined with the use of user namespace's will allow hardening > protections to be built to mitigate container escapes that utilize TTY > ioctls such as TIOCSTI. > > See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 > > Signed-off-by: Matt Brown <matt@nmatt.com> Acked-by: Serge Hallyn <serge@hallyn.com> > --- > drivers/tty/tty_io.c | 2 ++ > include/linux/tty.h | 2 ++ > 2 files changed, 4 insertions(+) > > diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c > index e6d1a65..c276814 100644 > --- a/drivers/tty/tty_io.c > +++ b/drivers/tty/tty_io.c > @@ -171,6 +171,7 @@ static void free_tty_struct(struct tty_struct *tty) > put_device(tty->dev); > kfree(tty->write_buf); > tty->magic = 0xDEADDEAD; > + put_user_ns(tty->owner_user_ns); > kfree(tty); > } > > @@ -3191,6 +3192,7 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx) > tty->index = idx; > tty_line_name(driver, idx, tty->name); > tty->dev = tty_get_device(tty); > + tty->owner_user_ns = get_user_ns(current_user_ns()); > > return tty; > } > diff --git a/include/linux/tty.h b/include/linux/tty.h > index 1017e904..d902d42 100644 > --- a/include/linux/tty.h > +++ b/include/linux/tty.h > @@ -12,6 +12,7 @@ > #include <uapi/linux/tty.h> > #include <linux/rwsem.h> > #include <linux/llist.h> > +#include <linux/user_namespace.h> > > > /* > @@ -333,6 +334,7 @@ struct tty_struct { > /* If the tty has a pending do_SAK, queue it here - akpm */ > struct work_struct SAK_work; > struct tty_port *port; > + struct user_namespace *owner_user_ns; > }; > > /* Each of a tty's open files has private_data pointing to tty_file_private */ > -- > 2.10.2 -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 33+ messages in thread
* Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct 2017-04-24 13:57 ` Serge E. Hallyn (?) @ 2017-05-03 19:32 ` Kees Cook -1 siblings, 0 replies; 33+ messages in thread From: Kees Cook @ 2017-05-03 19:32 UTC (permalink / raw) To: Serge E. Hallyn, Greg KH Cc: Matt Brown, James Morris, Jiri Slaby, Jonathan Corbet, Andrew Morton, Jann Horn, kernel-hardening, linux-security-module, LKML, linux-doc On Mon, Apr 24, 2017 at 6:57 AM, Serge E. Hallyn <serge@hallyn.com> wrote: > Quoting Matt Brown (matt@nmatt.com): >> This patch adds struct user_namespace *owner_user_ns to the tty_struct. >> Then it is set to current_user_ns() in the alloc_tty_struct function. >> >> This is done to facilitate capability checks against the original user >> namespace that allocated the tty. >> >> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) >> >> This combined with the use of user namespace's will allow hardening >> protections to be built to mitigate container escapes that utilize TTY >> ioctls such as TIOCSTI. >> >> See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 >> >> Signed-off-by: Matt Brown <matt@nmatt.com> > > Acked-by: Serge Hallyn <serge@hallyn.com> This Ack didn't end up in the v5, but I think it stands, yes? Greg, is the v5 okay to pull for you or would a v6 with Acks/Reviews included be preferred? -Kees > >> --- >> drivers/tty/tty_io.c | 2 ++ >> include/linux/tty.h | 2 ++ >> 2 files changed, 4 insertions(+) >> >> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c >> index e6d1a65..c276814 100644 >> --- a/drivers/tty/tty_io.c >> +++ b/drivers/tty/tty_io.c >> @@ -171,6 +171,7 @@ static void free_tty_struct(struct tty_struct *tty) >> put_device(tty->dev); >> kfree(tty->write_buf); >> tty->magic = 0xDEADDEAD; >> + put_user_ns(tty->owner_user_ns); >> kfree(tty); >> } >> >> @@ -3191,6 +3192,7 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx) >> tty->index = idx; >> tty_line_name(driver, idx, tty->name); >> tty->dev = tty_get_device(tty); >> + tty->owner_user_ns = get_user_ns(current_user_ns()); >> >> return tty; >> } >> diff --git a/include/linux/tty.h b/include/linux/tty.h >> index 1017e904..d902d42 100644 >> --- a/include/linux/tty.h >> +++ b/include/linux/tty.h >> @@ -12,6 +12,7 @@ >> #include <uapi/linux/tty.h> >> #include <linux/rwsem.h> >> #include <linux/llist.h> >> +#include <linux/user_namespace.h> >> >> >> /* >> @@ -333,6 +334,7 @@ struct tty_struct { >> /* If the tty has a pending do_SAK, queue it here - akpm */ >> struct work_struct SAK_work; >> struct tty_port *port; >> + struct user_namespace *owner_user_ns; >> }; >> >> /* Each of a tty's open files has private_data pointing to tty_file_private */ >> -- >> 2.10.2 -- Kees Cook Pixel Security ^ permalink raw reply [flat|nested] 33+ messages in thread
* [kernel-hardening] Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct @ 2017-05-03 19:32 ` Kees Cook 0 siblings, 0 replies; 33+ messages in thread From: Kees Cook @ 2017-05-03 19:32 UTC (permalink / raw) To: Serge E. Hallyn, Greg KH Cc: Matt Brown, James Morris, Jiri Slaby, Jonathan Corbet, Andrew Morton, Jann Horn, kernel-hardening, linux-security-module, LKML, linux-doc On Mon, Apr 24, 2017 at 6:57 AM, Serge E. Hallyn <serge@hallyn.com> wrote: > Quoting Matt Brown (matt@nmatt.com): >> This patch adds struct user_namespace *owner_user_ns to the tty_struct. >> Then it is set to current_user_ns() in the alloc_tty_struct function. >> >> This is done to facilitate capability checks against the original user >> namespace that allocated the tty. >> >> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) >> >> This combined with the use of user namespace's will allow hardening >> protections to be built to mitigate container escapes that utilize TTY >> ioctls such as TIOCSTI. >> >> See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 >> >> Signed-off-by: Matt Brown <matt@nmatt.com> > > Acked-by: Serge Hallyn <serge@hallyn.com> This Ack didn't end up in the v5, but I think it stands, yes? Greg, is the v5 okay to pull for you or would a v6 with Acks/Reviews included be preferred? -Kees > >> --- >> drivers/tty/tty_io.c | 2 ++ >> include/linux/tty.h | 2 ++ >> 2 files changed, 4 insertions(+) >> >> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c >> index e6d1a65..c276814 100644 >> --- a/drivers/tty/tty_io.c >> +++ b/drivers/tty/tty_io.c >> @@ -171,6 +171,7 @@ static void free_tty_struct(struct tty_struct *tty) >> put_device(tty->dev); >> kfree(tty->write_buf); >> tty->magic = 0xDEADDEAD; >> + put_user_ns(tty->owner_user_ns); >> kfree(tty); >> } >> >> @@ -3191,6 +3192,7 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx) >> tty->index = idx; >> tty_line_name(driver, idx, tty->name); >> tty->dev = tty_get_device(tty); >> + tty->owner_user_ns = get_user_ns(current_user_ns()); >> >> return tty; >> } >> diff --git a/include/linux/tty.h b/include/linux/tty.h >> index 1017e904..d902d42 100644 >> --- a/include/linux/tty.h >> +++ b/include/linux/tty.h >> @@ -12,6 +12,7 @@ >> #include <uapi/linux/tty.h> >> #include <linux/rwsem.h> >> #include <linux/llist.h> >> +#include <linux/user_namespace.h> >> >> >> /* >> @@ -333,6 +334,7 @@ struct tty_struct { >> /* If the tty has a pending do_SAK, queue it here - akpm */ >> struct work_struct SAK_work; >> struct tty_port *port; >> + struct user_namespace *owner_user_ns; >> }; >> >> /* Each of a tty's open files has private_data pointing to tty_file_private */ >> -- >> 2.10.2 -- Kees Cook Pixel Security ^ permalink raw reply [flat|nested] 33+ messages in thread
* [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct @ 2017-05-03 19:32 ` Kees Cook 0 siblings, 0 replies; 33+ messages in thread From: Kees Cook @ 2017-05-03 19:32 UTC (permalink / raw) To: linux-security-module On Mon, Apr 24, 2017 at 6:57 AM, Serge E. Hallyn <serge@hallyn.com> wrote: > Quoting Matt Brown (matt at nmatt.com): >> This patch adds struct user_namespace *owner_user_ns to the tty_struct. >> Then it is set to current_user_ns() in the alloc_tty_struct function. >> >> This is done to facilitate capability checks against the original user >> namespace that allocated the tty. >> >> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) >> >> This combined with the use of user namespace's will allow hardening >> protections to be built to mitigate container escapes that utilize TTY >> ioctls such as TIOCSTI. >> >> See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 >> >> Signed-off-by: Matt Brown <matt@nmatt.com> > > Acked-by: Serge Hallyn <serge@hallyn.com> This Ack didn't end up in the v5, but I think it stands, yes? Greg, is the v5 okay to pull for you or would a v6 with Acks/Reviews included be preferred? -Kees > >> --- >> drivers/tty/tty_io.c | 2 ++ >> include/linux/tty.h | 2 ++ >> 2 files changed, 4 insertions(+) >> >> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c >> index e6d1a65..c276814 100644 >> --- a/drivers/tty/tty_io.c >> +++ b/drivers/tty/tty_io.c >> @@ -171,6 +171,7 @@ static void free_tty_struct(struct tty_struct *tty) >> put_device(tty->dev); >> kfree(tty->write_buf); >> tty->magic = 0xDEADDEAD; >> + put_user_ns(tty->owner_user_ns); >> kfree(tty); >> } >> >> @@ -3191,6 +3192,7 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx) >> tty->index = idx; >> tty_line_name(driver, idx, tty->name); >> tty->dev = tty_get_device(tty); >> + tty->owner_user_ns = get_user_ns(current_user_ns()); >> >> return tty; >> } >> diff --git a/include/linux/tty.h b/include/linux/tty.h >> index 1017e904..d902d42 100644 >> --- a/include/linux/tty.h >> +++ b/include/linux/tty.h >> @@ -12,6 +12,7 @@ >> #include <uapi/linux/tty.h> >> #include <linux/rwsem.h> >> #include <linux/llist.h> >> +#include <linux/user_namespace.h> >> >> >> /* >> @@ -333,6 +334,7 @@ struct tty_struct { >> /* If the tty has a pending do_SAK, queue it here - akpm */ >> struct work_struct SAK_work; >> struct tty_port *port; >> + struct user_namespace *owner_user_ns; >> }; >> >> /* Each of a tty's open files has private_data pointing to tty_file_private */ >> -- >> 2.10.2 -- Kees Cook Pixel Security -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 33+ messages in thread
* Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct 2017-05-03 19:32 ` Kees Cook (?) @ 2017-05-03 19:45 ` Greg KH -1 siblings, 0 replies; 33+ messages in thread From: Greg KH @ 2017-05-03 19:45 UTC (permalink / raw) To: Kees Cook Cc: Serge E. Hallyn, Matt Brown, James Morris, Jiri Slaby, Jonathan Corbet, Andrew Morton, Jann Horn, kernel-hardening, linux-security-module, LKML, linux-doc On Wed, May 03, 2017 at 12:32:07PM -0700, Kees Cook wrote: > On Mon, Apr 24, 2017 at 6:57 AM, Serge E. Hallyn <serge@hallyn.com> wrote: > > Quoting Matt Brown (matt@nmatt.com): > >> This patch adds struct user_namespace *owner_user_ns to the tty_struct. > >> Then it is set to current_user_ns() in the alloc_tty_struct function. > >> > >> This is done to facilitate capability checks against the original user > >> namespace that allocated the tty. > >> > >> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) > >> > >> This combined with the use of user namespace's will allow hardening > >> protections to be built to mitigate container escapes that utilize TTY > >> ioctls such as TIOCSTI. > >> > >> See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 > >> > >> Signed-off-by: Matt Brown <matt@nmatt.com> > > > > Acked-by: Serge Hallyn <serge@hallyn.com> > > This Ack didn't end up in the v5, but I think it stands, yes? > > Greg, is the v5 okay to pull for you or would a v6 with Acks/Reviews > included be preferred? v6 would be great, and we are dropping patch 2 from the series, right? I was expecting this to be resent. I'll start looking at new patches like this after 4.12-rc1 is out. thanks, greg k-h ^ permalink raw reply [flat|nested] 33+ messages in thread
* [kernel-hardening] Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct @ 2017-05-03 19:45 ` Greg KH 0 siblings, 0 replies; 33+ messages in thread From: Greg KH @ 2017-05-03 19:45 UTC (permalink / raw) To: Kees Cook Cc: Serge E. Hallyn, Matt Brown, James Morris, Jiri Slaby, Jonathan Corbet, Andrew Morton, Jann Horn, kernel-hardening, linux-security-module, LKML, linux-doc On Wed, May 03, 2017 at 12:32:07PM -0700, Kees Cook wrote: > On Mon, Apr 24, 2017 at 6:57 AM, Serge E. Hallyn <serge@hallyn.com> wrote: > > Quoting Matt Brown (matt@nmatt.com): > >> This patch adds struct user_namespace *owner_user_ns to the tty_struct. > >> Then it is set to current_user_ns() in the alloc_tty_struct function. > >> > >> This is done to facilitate capability checks against the original user > >> namespace that allocated the tty. > >> > >> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) > >> > >> This combined with the use of user namespace's will allow hardening > >> protections to be built to mitigate container escapes that utilize TTY > >> ioctls such as TIOCSTI. > >> > >> See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 > >> > >> Signed-off-by: Matt Brown <matt@nmatt.com> > > > > Acked-by: Serge Hallyn <serge@hallyn.com> > > This Ack didn't end up in the v5, but I think it stands, yes? > > Greg, is the v5 okay to pull for you or would a v6 with Acks/Reviews > included be preferred? v6 would be great, and we are dropping patch 2 from the series, right? I was expecting this to be resent. I'll start looking at new patches like this after 4.12-rc1 is out. thanks, greg k-h ^ permalink raw reply [flat|nested] 33+ messages in thread
* [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct @ 2017-05-03 19:45 ` Greg KH 0 siblings, 0 replies; 33+ messages in thread From: Greg KH @ 2017-05-03 19:45 UTC (permalink / raw) To: linux-security-module On Wed, May 03, 2017 at 12:32:07PM -0700, Kees Cook wrote: > On Mon, Apr 24, 2017 at 6:57 AM, Serge E. Hallyn <serge@hallyn.com> wrote: > > Quoting Matt Brown (matt at nmatt.com): > >> This patch adds struct user_namespace *owner_user_ns to the tty_struct. > >> Then it is set to current_user_ns() in the alloc_tty_struct function. > >> > >> This is done to facilitate capability checks against the original user > >> namespace that allocated the tty. > >> > >> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) > >> > >> This combined with the use of user namespace's will allow hardening > >> protections to be built to mitigate container escapes that utilize TTY > >> ioctls such as TIOCSTI. > >> > >> See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 > >> > >> Signed-off-by: Matt Brown <matt@nmatt.com> > > > > Acked-by: Serge Hallyn <serge@hallyn.com> > > This Ack didn't end up in the v5, but I think it stands, yes? > > Greg, is the v5 okay to pull for you or would a v6 with Acks/Reviews > included be preferred? v6 would be great, and we are dropping patch 2 from the series, right? I was expecting this to be resent. I'll start looking at new patches like this after 4.12-rc1 is out. thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 33+ messages in thread
* Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct 2017-05-03 19:45 ` Greg KH (?) @ 2017-05-03 20:02 ` Matt Brown -1 siblings, 0 replies; 33+ messages in thread From: Matt Brown @ 2017-05-03 20:02 UTC (permalink / raw) To: Greg KH, Kees Cook Cc: Serge E. Hallyn, James Morris, Jiri Slaby, Jonathan Corbet, Andrew Morton, Jann Horn, kernel-hardening, linux-security-module, LKML, linux-doc On 05/03/2017 03:45 PM, Greg KH wrote: > On Wed, May 03, 2017 at 12:32:07PM -0700, Kees Cook wrote: >> On Mon, Apr 24, 2017 at 6:57 AM, Serge E. Hallyn <serge@hallyn.com> wrote: >>> Quoting Matt Brown (matt@nmatt.com): >>>> This patch adds struct user_namespace *owner_user_ns to the tty_struct. >>>> Then it is set to current_user_ns() in the alloc_tty_struct function. >>>> >>>> This is done to facilitate capability checks against the original user >>>> namespace that allocated the tty. >>>> >>>> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) >>>> >>>> This combined with the use of user namespace's will allow hardening >>>> protections to be built to mitigate container escapes that utilize TTY >>>> ioctls such as TIOCSTI. >>>> >>>> See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 >>>> >>>> Signed-off-by: Matt Brown <matt@nmatt.com> >>> >>> Acked-by: Serge Hallyn <serge@hallyn.com> >> >> This Ack didn't end up in the v5, but I think it stands, yes? >> >> Greg, is the v5 okay to pull for you or would a v6 with Acks/Reviews >> included be preferred? > > v6 would be great, and we are dropping patch 2 from the series, right? > I was expecting this to be resent. I'll start looking at new patches > like this after 4.12-rc1 is out. > I will create a v6 with the Acks/Reviews. I'd like to keep patch 2 in since that got acked by at least Serge. (Kees also? or just patch 1?) > thanks, > > greg k-h > ^ permalink raw reply [flat|nested] 33+ messages in thread
* [kernel-hardening] Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct @ 2017-05-03 20:02 ` Matt Brown 0 siblings, 0 replies; 33+ messages in thread From: Matt Brown @ 2017-05-03 20:02 UTC (permalink / raw) To: Greg KH, Kees Cook Cc: Serge E. Hallyn, James Morris, Jiri Slaby, Jonathan Corbet, Andrew Morton, Jann Horn, kernel-hardening, linux-security-module, LKML, linux-doc On 05/03/2017 03:45 PM, Greg KH wrote: > On Wed, May 03, 2017 at 12:32:07PM -0700, Kees Cook wrote: >> On Mon, Apr 24, 2017 at 6:57 AM, Serge E. Hallyn <serge@hallyn.com> wrote: >>> Quoting Matt Brown (matt@nmatt.com): >>>> This patch adds struct user_namespace *owner_user_ns to the tty_struct. >>>> Then it is set to current_user_ns() in the alloc_tty_struct function. >>>> >>>> This is done to facilitate capability checks against the original user >>>> namespace that allocated the tty. >>>> >>>> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) >>>> >>>> This combined with the use of user namespace's will allow hardening >>>> protections to be built to mitigate container escapes that utilize TTY >>>> ioctls such as TIOCSTI. >>>> >>>> See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 >>>> >>>> Signed-off-by: Matt Brown <matt@nmatt.com> >>> >>> Acked-by: Serge Hallyn <serge@hallyn.com> >> >> This Ack didn't end up in the v5, but I think it stands, yes? >> >> Greg, is the v5 okay to pull for you or would a v6 with Acks/Reviews >> included be preferred? > > v6 would be great, and we are dropping patch 2 from the series, right? > I was expecting this to be resent. I'll start looking at new patches > like this after 4.12-rc1 is out. > I will create a v6 with the Acks/Reviews. I'd like to keep patch 2 in since that got acked by at least Serge. (Kees also? or just patch 1?) > thanks, > > greg k-h > ^ permalink raw reply [flat|nested] 33+ messages in thread
* [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct @ 2017-05-03 20:02 ` Matt Brown 0 siblings, 0 replies; 33+ messages in thread From: Matt Brown @ 2017-05-03 20:02 UTC (permalink / raw) To: linux-security-module On 05/03/2017 03:45 PM, Greg KH wrote: > On Wed, May 03, 2017 at 12:32:07PM -0700, Kees Cook wrote: >> On Mon, Apr 24, 2017 at 6:57 AM, Serge E. Hallyn <serge@hallyn.com> wrote: >>> Quoting Matt Brown (matt at nmatt.com): >>>> This patch adds struct user_namespace *owner_user_ns to the tty_struct. >>>> Then it is set to current_user_ns() in the alloc_tty_struct function. >>>> >>>> This is done to facilitate capability checks against the original user >>>> namespace that allocated the tty. >>>> >>>> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) >>>> >>>> This combined with the use of user namespace's will allow hardening >>>> protections to be built to mitigate container escapes that utilize TTY >>>> ioctls such as TIOCSTI. >>>> >>>> See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 >>>> >>>> Signed-off-by: Matt Brown <matt@nmatt.com> >>> >>> Acked-by: Serge Hallyn <serge@hallyn.com> >> >> This Ack didn't end up in the v5, but I think it stands, yes? >> >> Greg, is the v5 okay to pull for you or would a v6 with Acks/Reviews >> included be preferred? > > v6 would be great, and we are dropping patch 2 from the series, right? > I was expecting this to be resent. I'll start looking at new patches > like this after 4.12-rc1 is out. > I will create a v6 with the Acks/Reviews. I'd like to keep patch 2 in since that got acked by at least Serge. (Kees also? or just patch 1?) > thanks, > > greg k-h > -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 33+ messages in thread
* Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct 2017-05-03 20:02 ` Matt Brown (?) @ 2017-05-03 20:19 ` Kees Cook -1 siblings, 0 replies; 33+ messages in thread From: Kees Cook @ 2017-05-03 20:19 UTC (permalink / raw) To: Matt Brown, Greg KH, Serge E. Hallyn Cc: James Morris, Jiri Slaby, Jonathan Corbet, Andrew Morton, Jann Horn, kernel-hardening, linux-security-module, LKML, linux-doc On Wed, May 3, 2017 at 1:02 PM, Matt Brown <matt@nmatt.com> wrote: > On 05/03/2017 03:45 PM, Greg KH wrote: >> >> On Wed, May 03, 2017 at 12:32:07PM -0700, Kees Cook wrote: >>> >>> On Mon, Apr 24, 2017 at 6:57 AM, Serge E. Hallyn <serge@hallyn.com> >>> wrote: >>>> >>>> Quoting Matt Brown (matt@nmatt.com): >>>>> >>>>> This patch adds struct user_namespace *owner_user_ns to the tty_struct. >>>>> Then it is set to current_user_ns() in the alloc_tty_struct function. >>>>> >>>>> This is done to facilitate capability checks against the original user >>>>> namespace that allocated the tty. >>>>> >>>>> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) >>>>> >>>>> This combined with the use of user namespace's will allow hardening >>>>> protections to be built to mitigate container escapes that utilize TTY >>>>> ioctls such as TIOCSTI. >>>>> >>>>> See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 >>>>> >>>>> Signed-off-by: Matt Brown <matt@nmatt.com> >>>> >>>> >>>> Acked-by: Serge Hallyn <serge@hallyn.com> >>> >>> >>> This Ack didn't end up in the v5, but I think it stands, yes? >>> >>> Greg, is the v5 okay to pull for you or would a v6 with Acks/Reviews >>> included be preferred? >> >> >> v6 would be great, and we are dropping patch 2 from the series, right? >> I was expecting this to be resent. I'll start looking at new patches >> like this after 4.12-rc1 is out. >> > > I will create a v6 with the Acks/Reviews. I'd like to keep patch 2 in > since that got acked by at least Serge. (Kees also? or just patch 1?) Sorry, I meant that patch 2's ack from serge got dropped accidentally. i.e. he Acked v4, but it wasn't in v5. Serge, just to double-check, does your Ack stand? -Kees -- Kees Cook Pixel Security ^ permalink raw reply [flat|nested] 33+ messages in thread
* [kernel-hardening] Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct @ 2017-05-03 20:19 ` Kees Cook 0 siblings, 0 replies; 33+ messages in thread From: Kees Cook @ 2017-05-03 20:19 UTC (permalink / raw) To: Matt Brown, Greg KH, Serge E. Hallyn Cc: James Morris, Jiri Slaby, Jonathan Corbet, Andrew Morton, Jann Horn, kernel-hardening, linux-security-module, LKML, linux-doc On Wed, May 3, 2017 at 1:02 PM, Matt Brown <matt@nmatt.com> wrote: > On 05/03/2017 03:45 PM, Greg KH wrote: >> >> On Wed, May 03, 2017 at 12:32:07PM -0700, Kees Cook wrote: >>> >>> On Mon, Apr 24, 2017 at 6:57 AM, Serge E. Hallyn <serge@hallyn.com> >>> wrote: >>>> >>>> Quoting Matt Brown (matt@nmatt.com): >>>>> >>>>> This patch adds struct user_namespace *owner_user_ns to the tty_struct. >>>>> Then it is set to current_user_ns() in the alloc_tty_struct function. >>>>> >>>>> This is done to facilitate capability checks against the original user >>>>> namespace that allocated the tty. >>>>> >>>>> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) >>>>> >>>>> This combined with the use of user namespace's will allow hardening >>>>> protections to be built to mitigate container escapes that utilize TTY >>>>> ioctls such as TIOCSTI. >>>>> >>>>> See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 >>>>> >>>>> Signed-off-by: Matt Brown <matt@nmatt.com> >>>> >>>> >>>> Acked-by: Serge Hallyn <serge@hallyn.com> >>> >>> >>> This Ack didn't end up in the v5, but I think it stands, yes? >>> >>> Greg, is the v5 okay to pull for you or would a v6 with Acks/Reviews >>> included be preferred? >> >> >> v6 would be great, and we are dropping patch 2 from the series, right? >> I was expecting this to be resent. I'll start looking at new patches >> like this after 4.12-rc1 is out. >> > > I will create a v6 with the Acks/Reviews. I'd like to keep patch 2 in > since that got acked by at least Serge. (Kees also? or just patch 1?) Sorry, I meant that patch 2's ack from serge got dropped accidentally. i.e. he Acked v4, but it wasn't in v5. Serge, just to double-check, does your Ack stand? -Kees -- Kees Cook Pixel Security ^ permalink raw reply [flat|nested] 33+ messages in thread
* [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct @ 2017-05-03 20:19 ` Kees Cook 0 siblings, 0 replies; 33+ messages in thread From: Kees Cook @ 2017-05-03 20:19 UTC (permalink / raw) To: linux-security-module On Wed, May 3, 2017 at 1:02 PM, Matt Brown <matt@nmatt.com> wrote: > On 05/03/2017 03:45 PM, Greg KH wrote: >> >> On Wed, May 03, 2017 at 12:32:07PM -0700, Kees Cook wrote: >>> >>> On Mon, Apr 24, 2017 at 6:57 AM, Serge E. Hallyn <serge@hallyn.com> >>> wrote: >>>> >>>> Quoting Matt Brown (matt at nmatt.com): >>>>> >>>>> This patch adds struct user_namespace *owner_user_ns to the tty_struct. >>>>> Then it is set to current_user_ns() in the alloc_tty_struct function. >>>>> >>>>> This is done to facilitate capability checks against the original user >>>>> namespace that allocated the tty. >>>>> >>>>> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) >>>>> >>>>> This combined with the use of user namespace's will allow hardening >>>>> protections to be built to mitigate container escapes that utilize TTY >>>>> ioctls such as TIOCSTI. >>>>> >>>>> See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 >>>>> >>>>> Signed-off-by: Matt Brown <matt@nmatt.com> >>>> >>>> >>>> Acked-by: Serge Hallyn <serge@hallyn.com> >>> >>> >>> This Ack didn't end up in the v5, but I think it stands, yes? >>> >>> Greg, is the v5 okay to pull for you or would a v6 with Acks/Reviews >>> included be preferred? >> >> >> v6 would be great, and we are dropping patch 2 from the series, right? >> I was expecting this to be resent. I'll start looking at new patches >> like this after 4.12-rc1 is out. >> > > I will create a v6 with the Acks/Reviews. I'd like to keep patch 2 in > since that got acked by at least Serge. (Kees also? or just patch 1?) Sorry, I meant that patch 2's ack from serge got dropped accidentally. i.e. he Acked v4, but it wasn't in v5. Serge, just to double-check, does your Ack stand? -Kees -- Kees Cook Pixel Security -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 33+ messages in thread
* Re: [kernel-hardening] Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct 2017-05-03 20:19 ` Kees Cook (?) @ 2017-05-04 4:42 ` Serge E. Hallyn -1 siblings, 0 replies; 33+ messages in thread From: Serge E. Hallyn @ 2017-05-04 4:42 UTC (permalink / raw) To: Kees Cook Cc: Matt Brown, Greg KH, Serge E. Hallyn, James Morris, Jiri Slaby, Jonathan Corbet, Andrew Morton, Jann Horn, kernel-hardening, linux-security-module, LKML, linux-doc On Wed, May 03, 2017 at 01:19:41PM -0700, Kees Cook wrote: > On Wed, May 3, 2017 at 1:02 PM, Matt Brown <matt@nmatt.com> wrote: > > On 05/03/2017 03:45 PM, Greg KH wrote: > >> > >> On Wed, May 03, 2017 at 12:32:07PM -0700, Kees Cook wrote: > >>> > >>> On Mon, Apr 24, 2017 at 6:57 AM, Serge E. Hallyn <serge@hallyn.com> > >>> wrote: > >>>> > >>>> Quoting Matt Brown (matt@nmatt.com): > >>>>> > >>>>> This patch adds struct user_namespace *owner_user_ns to the tty_struct. > >>>>> Then it is set to current_user_ns() in the alloc_tty_struct function. > >>>>> > >>>>> This is done to facilitate capability checks against the original user > >>>>> namespace that allocated the tty. > >>>>> > >>>>> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) > >>>>> > >>>>> This combined with the use of user namespace's will allow hardening > >>>>> protections to be built to mitigate container escapes that utilize TTY > >>>>> ioctls such as TIOCSTI. > >>>>> > >>>>> See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 > >>>>> > >>>>> Signed-off-by: Matt Brown <matt@nmatt.com> > >>>> > >>>> > >>>> Acked-by: Serge Hallyn <serge@hallyn.com> > >>> > >>> > >>> This Ack didn't end up in the v5, but I think it stands, yes? > >>> > >>> Greg, is the v5 okay to pull for you or would a v6 with Acks/Reviews > >>> included be preferred? > >> > >> > >> v6 would be great, and we are dropping patch 2 from the series, right? > >> I was expecting this to be resent. I'll start looking at new patches > >> like this after 4.12-rc1 is out. > >> > > > > I will create a v6 with the Acks/Reviews. I'd like to keep patch 2 in > > since that got acked by at least Serge. (Kees also? or just patch 1?) > > Sorry, I meant that patch 2's ack from serge got dropped accidentally. > i.e. he Acked v4, but it wasn't in v5. > > Serge, just to double-check, does your Ack stand? Yes. thanks, -serge ^ permalink raw reply [flat|nested] 33+ messages in thread
* Re: [kernel-hardening] Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct @ 2017-05-04 4:42 ` Serge E. Hallyn 0 siblings, 0 replies; 33+ messages in thread From: Serge E. Hallyn @ 2017-05-04 4:42 UTC (permalink / raw) To: Kees Cook Cc: Matt Brown, Greg KH, Serge E. Hallyn, James Morris, Jiri Slaby, Jonathan Corbet, Andrew Morton, Jann Horn, kernel-hardening, linux-security-module, LKML, linux-doc On Wed, May 03, 2017 at 01:19:41PM -0700, Kees Cook wrote: > On Wed, May 3, 2017 at 1:02 PM, Matt Brown <matt@nmatt.com> wrote: > > On 05/03/2017 03:45 PM, Greg KH wrote: > >> > >> On Wed, May 03, 2017 at 12:32:07PM -0700, Kees Cook wrote: > >>> > >>> On Mon, Apr 24, 2017 at 6:57 AM, Serge E. Hallyn <serge@hallyn.com> > >>> wrote: > >>>> > >>>> Quoting Matt Brown (matt@nmatt.com): > >>>>> > >>>>> This patch adds struct user_namespace *owner_user_ns to the tty_struct. > >>>>> Then it is set to current_user_ns() in the alloc_tty_struct function. > >>>>> > >>>>> This is done to facilitate capability checks against the original user > >>>>> namespace that allocated the tty. > >>>>> > >>>>> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) > >>>>> > >>>>> This combined with the use of user namespace's will allow hardening > >>>>> protections to be built to mitigate container escapes that utilize TTY > >>>>> ioctls such as TIOCSTI. > >>>>> > >>>>> See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 > >>>>> > >>>>> Signed-off-by: Matt Brown <matt@nmatt.com> > >>>> > >>>> > >>>> Acked-by: Serge Hallyn <serge@hallyn.com> > >>> > >>> > >>> This Ack didn't end up in the v5, but I think it stands, yes? > >>> > >>> Greg, is the v5 okay to pull for you or would a v6 with Acks/Reviews > >>> included be preferred? > >> > >> > >> v6 would be great, and we are dropping patch 2 from the series, right? > >> I was expecting this to be resent. I'll start looking at new patches > >> like this after 4.12-rc1 is out. > >> > > > > I will create a v6 with the Acks/Reviews. I'd like to keep patch 2 in > > since that got acked by at least Serge. (Kees also? or just patch 1?) > > Sorry, I meant that patch 2's ack from serge got dropped accidentally. > i.e. he Acked v4, but it wasn't in v5. > > Serge, just to double-check, does your Ack stand? Yes. thanks, -serge ^ permalink raw reply [flat|nested] 33+ messages in thread
* [kernel-hardening] Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct @ 2017-05-04 4:42 ` Serge E. Hallyn 0 siblings, 0 replies; 33+ messages in thread From: Serge E. Hallyn @ 2017-05-04 4:42 UTC (permalink / raw) To: linux-security-module On Wed, May 03, 2017 at 01:19:41PM -0700, Kees Cook wrote: > On Wed, May 3, 2017 at 1:02 PM, Matt Brown <matt@nmatt.com> wrote: > > On 05/03/2017 03:45 PM, Greg KH wrote: > >> > >> On Wed, May 03, 2017 at 12:32:07PM -0700, Kees Cook wrote: > >>> > >>> On Mon, Apr 24, 2017 at 6:57 AM, Serge E. Hallyn <serge@hallyn.com> > >>> wrote: > >>>> > >>>> Quoting Matt Brown (matt at nmatt.com): > >>>>> > >>>>> This patch adds struct user_namespace *owner_user_ns to the tty_struct. > >>>>> Then it is set to current_user_ns() in the alloc_tty_struct function. > >>>>> > >>>>> This is done to facilitate capability checks against the original user > >>>>> namespace that allocated the tty. > >>>>> > >>>>> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) > >>>>> > >>>>> This combined with the use of user namespace's will allow hardening > >>>>> protections to be built to mitigate container escapes that utilize TTY > >>>>> ioctls such as TIOCSTI. > >>>>> > >>>>> See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256 > >>>>> > >>>>> Signed-off-by: Matt Brown <matt@nmatt.com> > >>>> > >>>> > >>>> Acked-by: Serge Hallyn <serge@hallyn.com> > >>> > >>> > >>> This Ack didn't end up in the v5, but I think it stands, yes? > >>> > >>> Greg, is the v5 okay to pull for you or would a v6 with Acks/Reviews > >>> included be preferred? > >> > >> > >> v6 would be great, and we are dropping patch 2 from the series, right? > >> I was expecting this to be resent. I'll start looking at new patches > >> like this after 4.12-rc1 is out. > >> > > > > I will create a v6 with the Acks/Reviews. I'd like to keep patch 2 in > > since that got acked by at least Serge. (Kees also? or just patch 1?) > > Sorry, I meant that patch 2's ack from serge got dropped accidentally. > i.e. he Acked v4, but it wasn't in v5. > > Serge, just to double-check, does your Ack stand? Yes. thanks, -serge -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 33+ messages in thread
* Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct 2017-04-24 5:15 ` Matt Brown (?) @ 2017-04-25 14:55 ` Alan Cox -1 siblings, 0 replies; 33+ messages in thread From: Alan Cox @ 2017-04-25 14:55 UTC (permalink / raw) To: Matt Brown Cc: serge, jmorris, gregkh, jslaby, corbet, keescook, akpm, jannh, kernel-hardening, linux-security-module, linux-kernel, linux-doc On Mon, 24 Apr 2017 01:15:11 -0400 Matt Brown <matt@nmatt.com> wrote: > This patch adds struct user_namespace *owner_user_ns to the tty_struct. > Then it is set to current_user_ns() in the alloc_tty_struct function. > > This is done to facilitate capability checks against the original user > namespace that allocated the tty. > > E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) > > This combined with the use of user namespace's will allow hardening > protections to be built to mitigate container escapes that utilize TTY > ioctls such as TIOCSTI. Regardles of the TIOCSTI usefulness this makes complete sense. Alan ^ permalink raw reply [flat|nested] 33+ messages in thread
* [kernel-hardening] Re: [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct @ 2017-04-25 14:55 ` Alan Cox 0 siblings, 0 replies; 33+ messages in thread From: Alan Cox @ 2017-04-25 14:55 UTC (permalink / raw) To: Matt Brown Cc: serge, jmorris, gregkh, jslaby, corbet, keescook, akpm, jannh, kernel-hardening, linux-security-module, linux-kernel, linux-doc On Mon, 24 Apr 2017 01:15:11 -0400 Matt Brown <matt@nmatt.com> wrote: > This patch adds struct user_namespace *owner_user_ns to the tty_struct. > Then it is set to current_user_ns() in the alloc_tty_struct function. > > This is done to facilitate capability checks against the original user > namespace that allocated the tty. > > E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) > > This combined with the use of user namespace's will allow hardening > protections to be built to mitigate container escapes that utilize TTY > ioctls such as TIOCSTI. Regardles of the TIOCSTI usefulness this makes complete sense. Alan ^ permalink raw reply [flat|nested] 33+ messages in thread
* [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct @ 2017-04-25 14:55 ` Alan Cox 0 siblings, 0 replies; 33+ messages in thread From: Alan Cox @ 2017-04-25 14:55 UTC (permalink / raw) To: linux-security-module On Mon, 24 Apr 2017 01:15:11 -0400 Matt Brown <matt@nmatt.com> wrote: > This patch adds struct user_namespace *owner_user_ns to the tty_struct. > Then it is set to current_user_ns() in the alloc_tty_struct function. > > This is done to facilitate capability checks against the original user > namespace that allocated the tty. > > E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN) > > This combined with the use of user namespace's will allow hardening > protections to be built to mitigate container escapes that utilize TTY > ioctls such as TIOCSTI. Regardles of the TIOCSTI usefulness this makes complete sense. Alan -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 33+ messages in thread
* [PATCH v4 2/2] tiocsti-restrict : make TIOCSTI ioctl require CAP_SYS_ADMIN 2017-04-24 5:15 ` Matt Brown (?) @ 2017-04-24 5:15 ` Matt Brown -1 siblings, 0 replies; 33+ messages in thread From: Matt Brown @ 2017-04-24 5:15 UTC (permalink / raw) To: serge, jmorris, gregkh, jslaby, corbet, keescook Cc: akpm, jannh, kernel-hardening, linux-security-module, linux-kernel, linux-doc, Matt Brown This introduces the tiocsti_restrict sysctl, whose default is controlled via CONFIG_SECURITY_TIOCSTI_RESTRICT. When activated, this control restricts all TIOCSTI ioctl calls from non CAP_SYS_ADMIN users. This patch depends on patch 1/2 This patch was inspired from GRKERNSEC_HARDEN_TTY. This patch would have prevented https://bugzilla.redhat.com/show_bug.cgi?id=1411256 under the following conditions: * non-privileged container * container run inside new user namespace Possible effects on userland: There could be a few user programs that would be effected by this change. See: <https://codesearch.debian.net/search?q=ioctl%5C%28.*TIOCSTI> notable programs are: agetty, csh, xemacs and tcsh However, I still believe that this change is worth it given that the Kconfig defaults to n. This will be a feature that is turned on for the same reason that people activate it when using grsecurity. Users of this opt-in feature will realize that they are choosing security over some OS features like unprivileged TIOCSTI ioctls, as should be clear in the Kconfig help message. Threat Model/Patch Rational: >From grsecurity's config for GRKERNSEC_HARDEN_TTY. | There are very few legitimate uses for this functionality and it | has made vulnerabilities in several 'su'-like programs possible in | the past. Even without these vulnerabilities, it provides an | attacker with an easy mechanism to move laterally among other | processes within the same user's compromised session. So if one process within a tty session becomes compromised it can follow that additional processes, that are thought to be in different security boundaries, can be compromised as a result. When using a program like su or sudo, these additional processes could be in a tty session where TTY file descriptors are indeed shared over privilege boundaries. This is also an excellent writeup about the issue: <http://www.halfdog.net/Security/2012/TtyPushbackPrivilegeEscalation/> When user namespaces are in use, the check for the capability CAP_SYS_ADMIN is done against the user namespace that originally opened the tty. Signed-off-by: Matt Brown <matt@nmatt.com> --- Documentation/sysctl/kernel.txt | 21 +++++++++++++++++++++ drivers/tty/tty_io.c | 6 ++++++ include/linux/tty.h | 2 ++ kernel/sysctl.c | 12 ++++++++++++ security/Kconfig | 13 +++++++++++++ 5 files changed, 54 insertions(+) diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index bac23c1..c15c660 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -89,6 +89,7 @@ show up in /proc/sys/kernel: - sysctl_writes_strict - tainted - threads-max +- tiocsti_restrict - unknown_nmi_panic - watchdog - watchdog_thresh @@ -987,6 +988,26 @@ available RAM pages threads-max is reduced accordingly. ============================================================== +tiocsti_restrict: + +This toggle indicates whether unprivileged users are prevented +from using the TIOCSTI ioctl to inject commands into otherprocesses +which share a tty session. + +When tiocsti_restrict is set to (0) there are no restrictions(accept +the default restriction of only being able to injection commands into +one's own tty). When tiocsti_restrict is set to (1), users must +have CAP_SYS_ADMIN to use the TIOCSTI ioctl. + +When user namespaces are in use, the check for the capability +CAP_SYS_ADMIN is done against the user namespace that originally +opened the tty. + +The kernel config option CONFIG_SECURITY_TIOCSTI_RESTRICT sets the +default value of tiocsti_restrict. + +============================================================== + unknown_nmi_panic: The value in this file affects behavior of handling NMI. When the diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index c276814..fe68d14 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -2297,11 +2297,17 @@ static int tty_fasync(int fd, struct file *filp, int on) * FIXME: may race normal receive processing */ +int tiocsti_restrict = IS_ENABLED(CONFIG_SECURITY_TIOCSTI_RESTRICT); + static int tiocsti(struct tty_struct *tty, char __user *p) { char ch, mbz = 0; struct tty_ldisc *ld; + if (tiocsti_restrict && !ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN)) { + pr_warn_ratelimited("TIOCSTI ioctl call blocked for non-privileged process\n"); + return -EPERM; + } if ((current->signal->tty != tty) && !capable(CAP_SYS_ADMIN)) return -EPERM; if (get_user(ch, p)) diff --git a/include/linux/tty.h b/include/linux/tty.h index d902d42..2fd7f49 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -344,6 +344,8 @@ struct tty_file_private { struct list_head list; }; +extern int tiocsti_restrict; + /* tty magic number */ #define TTY_MAGIC 0x5401 diff --git a/kernel/sysctl.c b/kernel/sysctl.c index acf0a5a..68d1363 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -67,6 +67,7 @@ #include <linux/kexec.h> #include <linux/bpf.h> #include <linux/mount.h> +#include <linux/tty.h> #include <linux/uaccess.h> #include <asm/processor.h> @@ -833,6 +834,17 @@ static struct ctl_table kern_table[] = { .extra2 = &two, }, #endif +#if defined CONFIG_TTY + { + .procname = "tiocsti_restrict", + .data = &tiocsti_restrict, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec_minmax_sysadmin, + .extra1 = &zero, + .extra2 = &one, + }, +#endif { .procname = "ngroups_max", .data = &ngroups_max, diff --git a/security/Kconfig b/security/Kconfig index 3ff1bf9..7d13331 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -18,6 +18,19 @@ config SECURITY_DMESG_RESTRICT If you are unsure how to answer this question, answer N. +config SECURITY_TIOCSTI_RESTRICT + bool "Restrict unprivileged use of tiocsti command injection" + default n + help + This enforces restrictions on unprivileged users injecting commands + into other processes which share a tty session using the TIOCSTI + ioctl. This option makes TIOCSTI use require CAP_SYS_ADMIN. + + If this option is not selected, no restrictions will be enforced + unless the tiocsti_restrict sysctl is explicitly set to (1). + + If you are unsure how to answer this question, answer N. + config SECURITY bool "Enable different security models" depends on SYSFS -- 2.10.2 ^ permalink raw reply related [flat|nested] 33+ messages in thread
* [kernel-hardening] [PATCH v4 2/2] tiocsti-restrict : make TIOCSTI ioctl require CAP_SYS_ADMIN @ 2017-04-24 5:15 ` Matt Brown 0 siblings, 0 replies; 33+ messages in thread From: Matt Brown @ 2017-04-24 5:15 UTC (permalink / raw) To: serge, jmorris, gregkh, jslaby, corbet, keescook Cc: akpm, jannh, kernel-hardening, linux-security-module, linux-kernel, linux-doc, Matt Brown This introduces the tiocsti_restrict sysctl, whose default is controlled via CONFIG_SECURITY_TIOCSTI_RESTRICT. When activated, this control restricts all TIOCSTI ioctl calls from non CAP_SYS_ADMIN users. This patch depends on patch 1/2 This patch was inspired from GRKERNSEC_HARDEN_TTY. This patch would have prevented https://bugzilla.redhat.com/show_bug.cgi?id=1411256 under the following conditions: * non-privileged container * container run inside new user namespace Possible effects on userland: There could be a few user programs that would be effected by this change. See: <https://codesearch.debian.net/search?q=ioctl%5C%28.*TIOCSTI> notable programs are: agetty, csh, xemacs and tcsh However, I still believe that this change is worth it given that the Kconfig defaults to n. This will be a feature that is turned on for the same reason that people activate it when using grsecurity. Users of this opt-in feature will realize that they are choosing security over some OS features like unprivileged TIOCSTI ioctls, as should be clear in the Kconfig help message. Threat Model/Patch Rational: >From grsecurity's config for GRKERNSEC_HARDEN_TTY. | There are very few legitimate uses for this functionality and it | has made vulnerabilities in several 'su'-like programs possible in | the past. Even without these vulnerabilities, it provides an | attacker with an easy mechanism to move laterally among other | processes within the same user's compromised session. So if one process within a tty session becomes compromised it can follow that additional processes, that are thought to be in different security boundaries, can be compromised as a result. When using a program like su or sudo, these additional processes could be in a tty session where TTY file descriptors are indeed shared over privilege boundaries. This is also an excellent writeup about the issue: <http://www.halfdog.net/Security/2012/TtyPushbackPrivilegeEscalation/> When user namespaces are in use, the check for the capability CAP_SYS_ADMIN is done against the user namespace that originally opened the tty. Signed-off-by: Matt Brown <matt@nmatt.com> --- Documentation/sysctl/kernel.txt | 21 +++++++++++++++++++++ drivers/tty/tty_io.c | 6 ++++++ include/linux/tty.h | 2 ++ kernel/sysctl.c | 12 ++++++++++++ security/Kconfig | 13 +++++++++++++ 5 files changed, 54 insertions(+) diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index bac23c1..c15c660 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -89,6 +89,7 @@ show up in /proc/sys/kernel: - sysctl_writes_strict - tainted - threads-max +- tiocsti_restrict - unknown_nmi_panic - watchdog - watchdog_thresh @@ -987,6 +988,26 @@ available RAM pages threads-max is reduced accordingly. ============================================================== +tiocsti_restrict: + +This toggle indicates whether unprivileged users are prevented +from using the TIOCSTI ioctl to inject commands into otherprocesses +which share a tty session. + +When tiocsti_restrict is set to (0) there are no restrictions(accept +the default restriction of only being able to injection commands into +one's own tty). When tiocsti_restrict is set to (1), users must +have CAP_SYS_ADMIN to use the TIOCSTI ioctl. + +When user namespaces are in use, the check for the capability +CAP_SYS_ADMIN is done against the user namespace that originally +opened the tty. + +The kernel config option CONFIG_SECURITY_TIOCSTI_RESTRICT sets the +default value of tiocsti_restrict. + +============================================================== + unknown_nmi_panic: The value in this file affects behavior of handling NMI. When the diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index c276814..fe68d14 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -2297,11 +2297,17 @@ static int tty_fasync(int fd, struct file *filp, int on) * FIXME: may race normal receive processing */ +int tiocsti_restrict = IS_ENABLED(CONFIG_SECURITY_TIOCSTI_RESTRICT); + static int tiocsti(struct tty_struct *tty, char __user *p) { char ch, mbz = 0; struct tty_ldisc *ld; + if (tiocsti_restrict && !ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN)) { + pr_warn_ratelimited("TIOCSTI ioctl call blocked for non-privileged process\n"); + return -EPERM; + } if ((current->signal->tty != tty) && !capable(CAP_SYS_ADMIN)) return -EPERM; if (get_user(ch, p)) diff --git a/include/linux/tty.h b/include/linux/tty.h index d902d42..2fd7f49 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -344,6 +344,8 @@ struct tty_file_private { struct list_head list; }; +extern int tiocsti_restrict; + /* tty magic number */ #define TTY_MAGIC 0x5401 diff --git a/kernel/sysctl.c b/kernel/sysctl.c index acf0a5a..68d1363 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -67,6 +67,7 @@ #include <linux/kexec.h> #include <linux/bpf.h> #include <linux/mount.h> +#include <linux/tty.h> #include <linux/uaccess.h> #include <asm/processor.h> @@ -833,6 +834,17 @@ static struct ctl_table kern_table[] = { .extra2 = &two, }, #endif +#if defined CONFIG_TTY + { + .procname = "tiocsti_restrict", + .data = &tiocsti_restrict, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec_minmax_sysadmin, + .extra1 = &zero, + .extra2 = &one, + }, +#endif { .procname = "ngroups_max", .data = &ngroups_max, diff --git a/security/Kconfig b/security/Kconfig index 3ff1bf9..7d13331 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -18,6 +18,19 @@ config SECURITY_DMESG_RESTRICT If you are unsure how to answer this question, answer N. +config SECURITY_TIOCSTI_RESTRICT + bool "Restrict unprivileged use of tiocsti command injection" + default n + help + This enforces restrictions on unprivileged users injecting commands + into other processes which share a tty session using the TIOCSTI + ioctl. This option makes TIOCSTI use require CAP_SYS_ADMIN. + + If this option is not selected, no restrictions will be enforced + unless the tiocsti_restrict sysctl is explicitly set to (1). + + If you are unsure how to answer this question, answer N. + config SECURITY bool "Enable different security models" depends on SYSFS -- 2.10.2 ^ permalink raw reply related [flat|nested] 33+ messages in thread
* [PATCH v4 2/2] tiocsti-restrict : make TIOCSTI ioctl require CAP_SYS_ADMIN @ 2017-04-24 5:15 ` Matt Brown 0 siblings, 0 replies; 33+ messages in thread From: Matt Brown @ 2017-04-24 5:15 UTC (permalink / raw) To: linux-security-module This introduces the tiocsti_restrict sysctl, whose default is controlled via CONFIG_SECURITY_TIOCSTI_RESTRICT. When activated, this control restricts all TIOCSTI ioctl calls from non CAP_SYS_ADMIN users. This patch depends on patch 1/2 This patch was inspired from GRKERNSEC_HARDEN_TTY. This patch would have prevented https://bugzilla.redhat.com/show_bug.cgi?id=1411256 under the following conditions: * non-privileged container * container run inside new user namespace Possible effects on userland: There could be a few user programs that would be effected by this change. See: <https://codesearch.debian.net/search?q=ioctl%5C%28.*TIOCSTI> notable programs are: agetty, csh, xemacs and tcsh However, I still believe that this change is worth it given that the Kconfig defaults to n. This will be a feature that is turned on for the same reason that people activate it when using grsecurity. Users of this opt-in feature will realize that they are choosing security over some OS features like unprivileged TIOCSTI ioctls, as should be clear in the Kconfig help message. Threat Model/Patch Rational: >From grsecurity's config for GRKERNSEC_HARDEN_TTY. | There are very few legitimate uses for this functionality and it | has made vulnerabilities in several 'su'-like programs possible in | the past. Even without these vulnerabilities, it provides an | attacker with an easy mechanism to move laterally among other | processes within the same user's compromised session. So if one process within a tty session becomes compromised it can follow that additional processes, that are thought to be in different security boundaries, can be compromised as a result. When using a program like su or sudo, these additional processes could be in a tty session where TTY file descriptors are indeed shared over privilege boundaries. This is also an excellent writeup about the issue: <http://www.halfdog.net/Security/2012/TtyPushbackPrivilegeEscalation/> When user namespaces are in use, the check for the capability CAP_SYS_ADMIN is done against the user namespace that originally opened the tty. Signed-off-by: Matt Brown <matt@nmatt.com> --- Documentation/sysctl/kernel.txt | 21 +++++++++++++++++++++ drivers/tty/tty_io.c | 6 ++++++ include/linux/tty.h | 2 ++ kernel/sysctl.c | 12 ++++++++++++ security/Kconfig | 13 +++++++++++++ 5 files changed, 54 insertions(+) diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index bac23c1..c15c660 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -89,6 +89,7 @@ show up in /proc/sys/kernel: - sysctl_writes_strict - tainted - threads-max +- tiocsti_restrict - unknown_nmi_panic - watchdog - watchdog_thresh @@ -987,6 +988,26 @@ available RAM pages threads-max is reduced accordingly. ============================================================== +tiocsti_restrict: + +This toggle indicates whether unprivileged users are prevented +from using the TIOCSTI ioctl to inject commands into otherprocesses +which share a tty session. + +When tiocsti_restrict is set to (0) there are no restrictions(accept +the default restriction of only being able to injection commands into +one's own tty). When tiocsti_restrict is set to (1), users must +have CAP_SYS_ADMIN to use the TIOCSTI ioctl. + +When user namespaces are in use, the check for the capability +CAP_SYS_ADMIN is done against the user namespace that originally +opened the tty. + +The kernel config option CONFIG_SECURITY_TIOCSTI_RESTRICT sets the +default value of tiocsti_restrict. + +============================================================== + unknown_nmi_panic: The value in this file affects behavior of handling NMI. When the diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index c276814..fe68d14 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -2297,11 +2297,17 @@ static int tty_fasync(int fd, struct file *filp, int on) * FIXME: may race normal receive processing */ +int tiocsti_restrict = IS_ENABLED(CONFIG_SECURITY_TIOCSTI_RESTRICT); + static int tiocsti(struct tty_struct *tty, char __user *p) { char ch, mbz = 0; struct tty_ldisc *ld; + if (tiocsti_restrict && !ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN)) { + pr_warn_ratelimited("TIOCSTI ioctl call blocked for non-privileged process\n"); + return -EPERM; + } if ((current->signal->tty != tty) && !capable(CAP_SYS_ADMIN)) return -EPERM; if (get_user(ch, p)) diff --git a/include/linux/tty.h b/include/linux/tty.h index d902d42..2fd7f49 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -344,6 +344,8 @@ struct tty_file_private { struct list_head list; }; +extern int tiocsti_restrict; + /* tty magic number */ #define TTY_MAGIC 0x5401 diff --git a/kernel/sysctl.c b/kernel/sysctl.c index acf0a5a..68d1363 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -67,6 +67,7 @@ #include <linux/kexec.h> #include <linux/bpf.h> #include <linux/mount.h> +#include <linux/tty.h> #include <linux/uaccess.h> #include <asm/processor.h> @@ -833,6 +834,17 @@ static struct ctl_table kern_table[] = { .extra2 = &two, }, #endif +#if defined CONFIG_TTY + { + .procname = "tiocsti_restrict", + .data = &tiocsti_restrict, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec_minmax_sysadmin, + .extra1 = &zero, + .extra2 = &one, + }, +#endif { .procname = "ngroups_max", .data = &ngroups_max, diff --git a/security/Kconfig b/security/Kconfig index 3ff1bf9..7d13331 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -18,6 +18,19 @@ config SECURITY_DMESG_RESTRICT If you are unsure how to answer this question, answer N. +config SECURITY_TIOCSTI_RESTRICT + bool "Restrict unprivileged use of tiocsti command injection" + default n + help + This enforces restrictions on unprivileged users injecting commands + into other processes which share a tty session using the TIOCSTI + ioctl. This option makes TIOCSTI use require CAP_SYS_ADMIN. + + If this option is not selected, no restrictions will be enforced + unless the tiocsti_restrict sysctl is explicitly set to (1). + + If you are unsure how to answer this question, answer N. + config SECURITY bool "Enable different security models" depends on SYSFS -- 2.10.2 -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply related [flat|nested] 33+ messages in thread
* Re: [PATCH v4 2/2] tiocsti-restrict : make TIOCSTI ioctl require CAP_SYS_ADMIN 2017-04-24 5:15 ` Matt Brown (?) @ 2017-04-24 13:59 ` Serge E. Hallyn -1 siblings, 0 replies; 33+ messages in thread From: Serge E. Hallyn @ 2017-04-24 13:59 UTC (permalink / raw) To: Matt Brown Cc: serge, jmorris, gregkh, jslaby, corbet, keescook, akpm, jannh, kernel-hardening, linux-security-module, linux-kernel, linux-doc Quoting Matt Brown (matt@nmatt.com): > This introduces the tiocsti_restrict sysctl, whose default is controlled via > CONFIG_SECURITY_TIOCSTI_RESTRICT. When activated, this control restricts > all TIOCSTI ioctl calls from non CAP_SYS_ADMIN users. > > This patch depends on patch 1/2 > > This patch was inspired from GRKERNSEC_HARDEN_TTY. > > This patch would have prevented > https://bugzilla.redhat.com/show_bug.cgi?id=1411256 under the following > conditions: > * non-privileged container > * container run inside new user namespace > > Possible effects on userland: > > There could be a few user programs that would be effected by this > change. > See: <https://codesearch.debian.net/search?q=ioctl%5C%28.*TIOCSTI> > notable programs are: agetty, csh, xemacs and tcsh > > However, I still believe that this change is worth it given that the > Kconfig defaults to n. This will be a feature that is turned on for the > same reason that people activate it when using grsecurity. Users of this > opt-in feature will realize that they are choosing security over some OS > features like unprivileged TIOCSTI ioctls, as should be clear in the > Kconfig help message. > > Threat Model/Patch Rational: > > >From grsecurity's config for GRKERNSEC_HARDEN_TTY. > > | There are very few legitimate uses for this functionality and it > | has made vulnerabilities in several 'su'-like programs possible in > | the past. Even without these vulnerabilities, it provides an > | attacker with an easy mechanism to move laterally among other > | processes within the same user's compromised session. > > So if one process within a tty session becomes compromised it can follow > that additional processes, that are thought to be in different security > boundaries, can be compromised as a result. When using a program like su > or sudo, these additional processes could be in a tty session where TTY file > descriptors are indeed shared over privilege boundaries. > > This is also an excellent writeup about the issue: > <http://www.halfdog.net/Security/2012/TtyPushbackPrivilegeEscalation/> > > When user namespaces are in use, the check for the capability > CAP_SYS_ADMIN is done against the user namespace that originally opened > the tty. > > Signed-off-by: Matt Brown <matt@nmatt.com> Acked-by: Serge Hallyn <serge@hallyn.com> (typo below) > --- > Documentation/sysctl/kernel.txt | 21 +++++++++++++++++++++ > drivers/tty/tty_io.c | 6 ++++++ > include/linux/tty.h | 2 ++ > kernel/sysctl.c | 12 ++++++++++++ > security/Kconfig | 13 +++++++++++++ > 5 files changed, 54 insertions(+) > > diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt > index bac23c1..c15c660 100644 > --- a/Documentation/sysctl/kernel.txt > +++ b/Documentation/sysctl/kernel.txt > @@ -89,6 +89,7 @@ show up in /proc/sys/kernel: > - sysctl_writes_strict > - tainted > - threads-max > +- tiocsti_restrict > - unknown_nmi_panic > - watchdog > - watchdog_thresh > @@ -987,6 +988,26 @@ available RAM pages threads-max is reduced accordingly. > > ============================================================== > > +tiocsti_restrict: > + > +This toggle indicates whether unprivileged users are prevented > +from using the TIOCSTI ioctl to inject commands into otherprocesses space between other processes > +which share a tty session. > + > +When tiocsti_restrict is set to (0) there are no restrictions(accept > +the default restriction of only being able to injection commands into > +one's own tty). When tiocsti_restrict is set to (1), users must > +have CAP_SYS_ADMIN to use the TIOCSTI ioctl. > + > +When user namespaces are in use, the check for the capability > +CAP_SYS_ADMIN is done against the user namespace that originally > +opened the tty. > + > +The kernel config option CONFIG_SECURITY_TIOCSTI_RESTRICT sets the > +default value of tiocsti_restrict. > + > +============================================================== > + > unknown_nmi_panic: > > The value in this file affects behavior of handling NMI. When the > diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c > index c276814..fe68d14 100644 > --- a/drivers/tty/tty_io.c > +++ b/drivers/tty/tty_io.c > @@ -2297,11 +2297,17 @@ static int tty_fasync(int fd, struct file *filp, int on) > * FIXME: may race normal receive processing > */ > > +int tiocsti_restrict = IS_ENABLED(CONFIG_SECURITY_TIOCSTI_RESTRICT); > + > static int tiocsti(struct tty_struct *tty, char __user *p) > { > char ch, mbz = 0; > struct tty_ldisc *ld; > > + if (tiocsti_restrict && !ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN)) { > + pr_warn_ratelimited("TIOCSTI ioctl call blocked for non-privileged process\n"); > + return -EPERM; > + } > if ((current->signal->tty != tty) && !capable(CAP_SYS_ADMIN)) > return -EPERM; > if (get_user(ch, p)) > diff --git a/include/linux/tty.h b/include/linux/tty.h > index d902d42..2fd7f49 100644 > --- a/include/linux/tty.h > +++ b/include/linux/tty.h > @@ -344,6 +344,8 @@ struct tty_file_private { > struct list_head list; > }; > > +extern int tiocsti_restrict; > + > /* tty magic number */ > #define TTY_MAGIC 0x5401 > > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index acf0a5a..68d1363 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -67,6 +67,7 @@ > #include <linux/kexec.h> > #include <linux/bpf.h> > #include <linux/mount.h> > +#include <linux/tty.h> > > #include <linux/uaccess.h> > #include <asm/processor.h> > @@ -833,6 +834,17 @@ static struct ctl_table kern_table[] = { > .extra2 = &two, > }, > #endif > +#if defined CONFIG_TTY > + { > + .procname = "tiocsti_restrict", > + .data = &tiocsti_restrict, > + .maxlen = sizeof(int), > + .mode = 0644, > + .proc_handler = proc_dointvec_minmax_sysadmin, > + .extra1 = &zero, > + .extra2 = &one, > + }, > +#endif > { > .procname = "ngroups_max", > .data = &ngroups_max, > diff --git a/security/Kconfig b/security/Kconfig > index 3ff1bf9..7d13331 100644 > --- a/security/Kconfig > +++ b/security/Kconfig > @@ -18,6 +18,19 @@ config SECURITY_DMESG_RESTRICT > > If you are unsure how to answer this question, answer N. > > +config SECURITY_TIOCSTI_RESTRICT > + bool "Restrict unprivileged use of tiocsti command injection" > + default n > + help > + This enforces restrictions on unprivileged users injecting commands > + into other processes which share a tty session using the TIOCSTI > + ioctl. This option makes TIOCSTI use require CAP_SYS_ADMIN. > + > + If this option is not selected, no restrictions will be enforced > + unless the tiocsti_restrict sysctl is explicitly set to (1). > + > + If you are unsure how to answer this question, answer N. > + > config SECURITY > bool "Enable different security models" > depends on SYSFS > -- > 2.10.2 ^ permalink raw reply [flat|nested] 33+ messages in thread
* [kernel-hardening] Re: [PATCH v4 2/2] tiocsti-restrict : make TIOCSTI ioctl require CAP_SYS_ADMIN @ 2017-04-24 13:59 ` Serge E. Hallyn 0 siblings, 0 replies; 33+ messages in thread From: Serge E. Hallyn @ 2017-04-24 13:59 UTC (permalink / raw) To: Matt Brown Cc: serge, jmorris, gregkh, jslaby, corbet, keescook, akpm, jannh, kernel-hardening, linux-security-module, linux-kernel, linux-doc Quoting Matt Brown (matt@nmatt.com): > This introduces the tiocsti_restrict sysctl, whose default is controlled via > CONFIG_SECURITY_TIOCSTI_RESTRICT. When activated, this control restricts > all TIOCSTI ioctl calls from non CAP_SYS_ADMIN users. > > This patch depends on patch 1/2 > > This patch was inspired from GRKERNSEC_HARDEN_TTY. > > This patch would have prevented > https://bugzilla.redhat.com/show_bug.cgi?id=1411256 under the following > conditions: > * non-privileged container > * container run inside new user namespace > > Possible effects on userland: > > There could be a few user programs that would be effected by this > change. > See: <https://codesearch.debian.net/search?q=ioctl%5C%28.*TIOCSTI> > notable programs are: agetty, csh, xemacs and tcsh > > However, I still believe that this change is worth it given that the > Kconfig defaults to n. This will be a feature that is turned on for the > same reason that people activate it when using grsecurity. Users of this > opt-in feature will realize that they are choosing security over some OS > features like unprivileged TIOCSTI ioctls, as should be clear in the > Kconfig help message. > > Threat Model/Patch Rational: > > >From grsecurity's config for GRKERNSEC_HARDEN_TTY. > > | There are very few legitimate uses for this functionality and it > | has made vulnerabilities in several 'su'-like programs possible in > | the past. Even without these vulnerabilities, it provides an > | attacker with an easy mechanism to move laterally among other > | processes within the same user's compromised session. > > So if one process within a tty session becomes compromised it can follow > that additional processes, that are thought to be in different security > boundaries, can be compromised as a result. When using a program like su > or sudo, these additional processes could be in a tty session where TTY file > descriptors are indeed shared over privilege boundaries. > > This is also an excellent writeup about the issue: > <http://www.halfdog.net/Security/2012/TtyPushbackPrivilegeEscalation/> > > When user namespaces are in use, the check for the capability > CAP_SYS_ADMIN is done against the user namespace that originally opened > the tty. > > Signed-off-by: Matt Brown <matt@nmatt.com> Acked-by: Serge Hallyn <serge@hallyn.com> (typo below) > --- > Documentation/sysctl/kernel.txt | 21 +++++++++++++++++++++ > drivers/tty/tty_io.c | 6 ++++++ > include/linux/tty.h | 2 ++ > kernel/sysctl.c | 12 ++++++++++++ > security/Kconfig | 13 +++++++++++++ > 5 files changed, 54 insertions(+) > > diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt > index bac23c1..c15c660 100644 > --- a/Documentation/sysctl/kernel.txt > +++ b/Documentation/sysctl/kernel.txt > @@ -89,6 +89,7 @@ show up in /proc/sys/kernel: > - sysctl_writes_strict > - tainted > - threads-max > +- tiocsti_restrict > - unknown_nmi_panic > - watchdog > - watchdog_thresh > @@ -987,6 +988,26 @@ available RAM pages threads-max is reduced accordingly. > > ============================================================== > > +tiocsti_restrict: > + > +This toggle indicates whether unprivileged users are prevented > +from using the TIOCSTI ioctl to inject commands into otherprocesses space between other processes > +which share a tty session. > + > +When tiocsti_restrict is set to (0) there are no restrictions(accept > +the default restriction of only being able to injection commands into > +one's own tty). When tiocsti_restrict is set to (1), users must > +have CAP_SYS_ADMIN to use the TIOCSTI ioctl. > + > +When user namespaces are in use, the check for the capability > +CAP_SYS_ADMIN is done against the user namespace that originally > +opened the tty. > + > +The kernel config option CONFIG_SECURITY_TIOCSTI_RESTRICT sets the > +default value of tiocsti_restrict. > + > +============================================================== > + > unknown_nmi_panic: > > The value in this file affects behavior of handling NMI. When the > diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c > index c276814..fe68d14 100644 > --- a/drivers/tty/tty_io.c > +++ b/drivers/tty/tty_io.c > @@ -2297,11 +2297,17 @@ static int tty_fasync(int fd, struct file *filp, int on) > * FIXME: may race normal receive processing > */ > > +int tiocsti_restrict = IS_ENABLED(CONFIG_SECURITY_TIOCSTI_RESTRICT); > + > static int tiocsti(struct tty_struct *tty, char __user *p) > { > char ch, mbz = 0; > struct tty_ldisc *ld; > > + if (tiocsti_restrict && !ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN)) { > + pr_warn_ratelimited("TIOCSTI ioctl call blocked for non-privileged process\n"); > + return -EPERM; > + } > if ((current->signal->tty != tty) && !capable(CAP_SYS_ADMIN)) > return -EPERM; > if (get_user(ch, p)) > diff --git a/include/linux/tty.h b/include/linux/tty.h > index d902d42..2fd7f49 100644 > --- a/include/linux/tty.h > +++ b/include/linux/tty.h > @@ -344,6 +344,8 @@ struct tty_file_private { > struct list_head list; > }; > > +extern int tiocsti_restrict; > + > /* tty magic number */ > #define TTY_MAGIC 0x5401 > > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index acf0a5a..68d1363 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -67,6 +67,7 @@ > #include <linux/kexec.h> > #include <linux/bpf.h> > #include <linux/mount.h> > +#include <linux/tty.h> > > #include <linux/uaccess.h> > #include <asm/processor.h> > @@ -833,6 +834,17 @@ static struct ctl_table kern_table[] = { > .extra2 = &two, > }, > #endif > +#if defined CONFIG_TTY > + { > + .procname = "tiocsti_restrict", > + .data = &tiocsti_restrict, > + .maxlen = sizeof(int), > + .mode = 0644, > + .proc_handler = proc_dointvec_minmax_sysadmin, > + .extra1 = &zero, > + .extra2 = &one, > + }, > +#endif > { > .procname = "ngroups_max", > .data = &ngroups_max, > diff --git a/security/Kconfig b/security/Kconfig > index 3ff1bf9..7d13331 100644 > --- a/security/Kconfig > +++ b/security/Kconfig > @@ -18,6 +18,19 @@ config SECURITY_DMESG_RESTRICT > > If you are unsure how to answer this question, answer N. > > +config SECURITY_TIOCSTI_RESTRICT > + bool "Restrict unprivileged use of tiocsti command injection" > + default n > + help > + This enforces restrictions on unprivileged users injecting commands > + into other processes which share a tty session using the TIOCSTI > + ioctl. This option makes TIOCSTI use require CAP_SYS_ADMIN. > + > + If this option is not selected, no restrictions will be enforced > + unless the tiocsti_restrict sysctl is explicitly set to (1). > + > + If you are unsure how to answer this question, answer N. > + > config SECURITY > bool "Enable different security models" > depends on SYSFS > -- > 2.10.2 ^ permalink raw reply [flat|nested] 33+ messages in thread
* [PATCH v4 2/2] tiocsti-restrict : make TIOCSTI ioctl require CAP_SYS_ADMIN @ 2017-04-24 13:59 ` Serge E. Hallyn 0 siblings, 0 replies; 33+ messages in thread From: Serge E. Hallyn @ 2017-04-24 13:59 UTC (permalink / raw) To: linux-security-module Quoting Matt Brown (matt at nmatt.com): > This introduces the tiocsti_restrict sysctl, whose default is controlled via > CONFIG_SECURITY_TIOCSTI_RESTRICT. When activated, this control restricts > all TIOCSTI ioctl calls from non CAP_SYS_ADMIN users. > > This patch depends on patch 1/2 > > This patch was inspired from GRKERNSEC_HARDEN_TTY. > > This patch would have prevented > https://bugzilla.redhat.com/show_bug.cgi?id=1411256 under the following > conditions: > * non-privileged container > * container run inside new user namespace > > Possible effects on userland: > > There could be a few user programs that would be effected by this > change. > See: <https://codesearch.debian.net/search?q=ioctl%5C%28.*TIOCSTI> > notable programs are: agetty, csh, xemacs and tcsh > > However, I still believe that this change is worth it given that the > Kconfig defaults to n. This will be a feature that is turned on for the > same reason that people activate it when using grsecurity. Users of this > opt-in feature will realize that they are choosing security over some OS > features like unprivileged TIOCSTI ioctls, as should be clear in the > Kconfig help message. > > Threat Model/Patch Rational: > > >From grsecurity's config for GRKERNSEC_HARDEN_TTY. > > | There are very few legitimate uses for this functionality and it > | has made vulnerabilities in several 'su'-like programs possible in > | the past. Even without these vulnerabilities, it provides an > | attacker with an easy mechanism to move laterally among other > | processes within the same user's compromised session. > > So if one process within a tty session becomes compromised it can follow > that additional processes, that are thought to be in different security > boundaries, can be compromised as a result. When using a program like su > or sudo, these additional processes could be in a tty session where TTY file > descriptors are indeed shared over privilege boundaries. > > This is also an excellent writeup about the issue: > <http://www.halfdog.net/Security/2012/TtyPushbackPrivilegeEscalation/> > > When user namespaces are in use, the check for the capability > CAP_SYS_ADMIN is done against the user namespace that originally opened > the tty. > > Signed-off-by: Matt Brown <matt@nmatt.com> Acked-by: Serge Hallyn <serge@hallyn.com> (typo below) > --- > Documentation/sysctl/kernel.txt | 21 +++++++++++++++++++++ > drivers/tty/tty_io.c | 6 ++++++ > include/linux/tty.h | 2 ++ > kernel/sysctl.c | 12 ++++++++++++ > security/Kconfig | 13 +++++++++++++ > 5 files changed, 54 insertions(+) > > diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt > index bac23c1..c15c660 100644 > --- a/Documentation/sysctl/kernel.txt > +++ b/Documentation/sysctl/kernel.txt > @@ -89,6 +89,7 @@ show up in /proc/sys/kernel: > - sysctl_writes_strict > - tainted > - threads-max > +- tiocsti_restrict > - unknown_nmi_panic > - watchdog > - watchdog_thresh > @@ -987,6 +988,26 @@ available RAM pages threads-max is reduced accordingly. > > ============================================================== > > +tiocsti_restrict: > + > +This toggle indicates whether unprivileged users are prevented > +from using the TIOCSTI ioctl to inject commands into otherprocesses space between other processes > +which share a tty session. > + > +When tiocsti_restrict is set to (0) there are no restrictions(accept > +the default restriction of only being able to injection commands into > +one's own tty). When tiocsti_restrict is set to (1), users must > +have CAP_SYS_ADMIN to use the TIOCSTI ioctl. > + > +When user namespaces are in use, the check for the capability > +CAP_SYS_ADMIN is done against the user namespace that originally > +opened the tty. > + > +The kernel config option CONFIG_SECURITY_TIOCSTI_RESTRICT sets the > +default value of tiocsti_restrict. > + > +============================================================== > + > unknown_nmi_panic: > > The value in this file affects behavior of handling NMI. When the > diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c > index c276814..fe68d14 100644 > --- a/drivers/tty/tty_io.c > +++ b/drivers/tty/tty_io.c > @@ -2297,11 +2297,17 @@ static int tty_fasync(int fd, struct file *filp, int on) > * FIXME: may race normal receive processing > */ > > +int tiocsti_restrict = IS_ENABLED(CONFIG_SECURITY_TIOCSTI_RESTRICT); > + > static int tiocsti(struct tty_struct *tty, char __user *p) > { > char ch, mbz = 0; > struct tty_ldisc *ld; > > + if (tiocsti_restrict && !ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN)) { > + pr_warn_ratelimited("TIOCSTI ioctl call blocked for non-privileged process\n"); > + return -EPERM; > + } > if ((current->signal->tty != tty) && !capable(CAP_SYS_ADMIN)) > return -EPERM; > if (get_user(ch, p)) > diff --git a/include/linux/tty.h b/include/linux/tty.h > index d902d42..2fd7f49 100644 > --- a/include/linux/tty.h > +++ b/include/linux/tty.h > @@ -344,6 +344,8 @@ struct tty_file_private { > struct list_head list; > }; > > +extern int tiocsti_restrict; > + > /* tty magic number */ > #define TTY_MAGIC 0x5401 > > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index acf0a5a..68d1363 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -67,6 +67,7 @@ > #include <linux/kexec.h> > #include <linux/bpf.h> > #include <linux/mount.h> > +#include <linux/tty.h> > > #include <linux/uaccess.h> > #include <asm/processor.h> > @@ -833,6 +834,17 @@ static struct ctl_table kern_table[] = { > .extra2 = &two, > }, > #endif > +#if defined CONFIG_TTY > + { > + .procname = "tiocsti_restrict", > + .data = &tiocsti_restrict, > + .maxlen = sizeof(int), > + .mode = 0644, > + .proc_handler = proc_dointvec_minmax_sysadmin, > + .extra1 = &zero, > + .extra2 = &one, > + }, > +#endif > { > .procname = "ngroups_max", > .data = &ngroups_max, > diff --git a/security/Kconfig b/security/Kconfig > index 3ff1bf9..7d13331 100644 > --- a/security/Kconfig > +++ b/security/Kconfig > @@ -18,6 +18,19 @@ config SECURITY_DMESG_RESTRICT > > If you are unsure how to answer this question, answer N. > > +config SECURITY_TIOCSTI_RESTRICT > + bool "Restrict unprivileged use of tiocsti command injection" > + default n > + help > + This enforces restrictions on unprivileged users injecting commands > + into other processes which share a tty session using the TIOCSTI > + ioctl. This option makes TIOCSTI use require CAP_SYS_ADMIN. > + > + If this option is not selected, no restrictions will be enforced > + unless the tiocsti_restrict sysctl is explicitly set to (1). > + > + If you are unsure how to answer this question, answer N. > + > config SECURITY > bool "Enable different security models" > depends on SYSFS > -- > 2.10.2 -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 33+ messages in thread
end of thread, other threads:[~2017-05-04 4:42 UTC | newest] Thread overview: 33+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2017-04-24 5:15 [PATCH v4 0/2] tiocsti-restrict : make TIOCSTI ioctl require CAP_SYS_ADMIN Matt Brown 2017-04-24 5:15 ` [kernel-hardening] " Matt Brown 2017-04-24 5:15 ` Matt Brown 2017-04-24 5:15 ` [PATCH v4 1/2] tiocsti-restrict : Add owner user namespace to tty_struct Matt Brown 2017-04-24 5:15 ` [kernel-hardening] " Matt Brown 2017-04-24 5:15 ` Matt Brown 2017-04-24 13:57 ` Serge E. Hallyn 2017-04-24 13:57 ` [kernel-hardening] " Serge E. Hallyn 2017-04-24 13:57 ` Serge E. Hallyn 2017-05-03 19:32 ` Kees Cook 2017-05-03 19:32 ` [kernel-hardening] " Kees Cook 2017-05-03 19:32 ` Kees Cook 2017-05-03 19:45 ` Greg KH 2017-05-03 19:45 ` [kernel-hardening] " Greg KH 2017-05-03 19:45 ` Greg KH 2017-05-03 20:02 ` Matt Brown 2017-05-03 20:02 ` [kernel-hardening] " Matt Brown 2017-05-03 20:02 ` Matt Brown 2017-05-03 20:19 ` Kees Cook 2017-05-03 20:19 ` [kernel-hardening] " Kees Cook 2017-05-03 20:19 ` Kees Cook 2017-05-04 4:42 ` [kernel-hardening] " Serge E. Hallyn 2017-05-04 4:42 ` Serge E. Hallyn 2017-05-04 4:42 ` Serge E. Hallyn 2017-04-25 14:55 ` Alan Cox 2017-04-25 14:55 ` [kernel-hardening] " Alan Cox 2017-04-25 14:55 ` Alan Cox 2017-04-24 5:15 ` [PATCH v4 2/2] tiocsti-restrict : make TIOCSTI ioctl require CAP_SYS_ADMIN Matt Brown 2017-04-24 5:15 ` [kernel-hardening] " Matt Brown 2017-04-24 5:15 ` Matt Brown 2017-04-24 13:59 ` Serge E. Hallyn 2017-04-24 13:59 ` [kernel-hardening] " Serge E. Hallyn 2017-04-24 13:59 ` Serge E. Hallyn
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