[PATCH] proc: use ns_capable instead of capable for timerslack_ns

[PATCH] proc: use ns_capable instead of capable for timerslack_ns

[bmgordon]

From: Benjamin Gordon <bmgordon@google.com>

Access to timerslack_ns is controlled by a process having CAP_SYS_NICE
in its effective capability set, but the current check looks in the root
namespace instead of the process' user namespace.  Since a process is
allowed to do other activities controlled by CAP_SYS_NICE inside a
namespace, it should also be able to adjust timerslack_ns.

Signed-off-by: Benjamin Gordon <bmgordon@google.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Oren Laadan <orenl@cellrox.com>
Cc: Ruchi Kandoi <kandoiruchi@google.com>
Cc: Rom Lemarchand <romlem@android.com>
Cc: Todd Kjos <tkjos@google.com>
Cc: Colin Cross <ccross@android.com>
Cc: Nick Kralevich <nnk@google.com>
Cc: Dmitry Shmidt <dimitrysh@google.com>
Cc: Elliott Hughes <enh@google.com>
Cc: Android Kernel Team <kernel-team@android.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 fs/proc/base.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 7e9f07bf260d..4b50937dff80 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2356,7 +2356,7 @@ static ssize_t timerslack_ns_write(struct file *file, const char __user *buf,
 		return -ESRCH;
 
 	if (p != current) {
-		if (!capable(CAP_SYS_NICE)) {
+		if (!ns_capable(file->f_cred->user_ns, CAP_SYS_NICE)) {
 			count = -EPERM;
 			goto out;
 		}
@@ -2393,7 +2393,7 @@ static int timerslack_ns_show(struct seq_file *m, void *v)
 
 	if (p != current) {
 
-		if (!capable(CAP_SYS_NICE)) {
+		if (!ns_capable(seq_user_ns(m), CAP_SYS_NICE)) {
 			err = -EPERM;
 			goto out;
 		}
-- 
2.19.1.331.ge82ca0e54c-goog

Re: [PATCH] proc: use ns_capable instead of capable for timerslack_ns

[Benjamin Gordon]

On Wed, Oct 17, 2018 at 04:47:38PM -0600, bmgordon@google.com wrote:
> Access to timerslack_ns is controlled by a process having CAP_SYS_NICE
> in its effective capability set, but the current check looks in the root
> namespace instead of the process' user namespace.  Since a process is
> allowed to do other activities controlled by CAP_SYS_NICE inside a
> namespace, it should also be able to adjust timerslack_ns.
> 
> Signed-off-by: Benjamin Gordon <bmgordon@google.com>
> Cc: John Stultz <john.stultz@linaro.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: "Serge E. Hallyn" <serge@hallyn.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Arjan van de Ven <arjan@linux.intel.com>
> Cc: Oren Laadan <orenl@cellrox.com>
> Cc: Ruchi Kandoi <kandoiruchi@google.com>
> Cc: Rom Lemarchand <romlem@android.com>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: Colin Cross <ccross@android.com>
> Cc: Nick Kralevich <nnk@google.com>
> Cc: Dmitry Shmidt <dimitrysh@google.com>
> Cc: Elliott Hughes <enh@google.com>
> Cc: Android Kernel Team <kernel-team@android.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> ---
>  fs/proc/base.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 7e9f07bf260d..4b50937dff80 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2356,7 +2356,7 @@ static ssize_t timerslack_ns_write(struct file *file, const char __user *buf,
>  		return -ESRCH;
>  
>  	if (p != current) {
> -		if (!capable(CAP_SYS_NICE)) {
> +		if (!ns_capable(file->f_cred->user_ns, CAP_SYS_NICE)) {
>  			count = -EPERM;
>  			goto out;
>  		}
> @@ -2393,7 +2393,7 @@ static int timerslack_ns_show(struct seq_file *m, void *v)
>  
>  	if (p != current) {
>  
> -		if (!capable(CAP_SYS_NICE)) {
> +		if (!ns_capable(seq_user_ns(m), CAP_SYS_NICE)) {
>  			err = -EPERM;
>  			goto out;
>  		}
> -- 
> 2.19.1.331.ge82ca0e54c-goog
> 

Friendly ping.  Does anybody have time to take a look at this?

Thanks,
Benjamin

Re: [PATCH] proc: use ns_capable instead of capable for timerslack_ns

[John Stultz]

On Wed, Oct 17, 2018 at 3:47 PM,  <bmgordon@google.com> wrote:
> From: Benjamin Gordon <bmgordon@google.com>
>
> Access to timerslack_ns is controlled by a process having CAP_SYS_NICE
> in its effective capability set, but the current check looks in the root
> namespace instead of the process' user namespace.  Since a process is
> allowed to do other activities controlled by CAP_SYS_NICE inside a
> namespace, it should also be able to adjust timerslack_ns.
>
> Signed-off-by: Benjamin Gordon <bmgordon@google.com>
> Cc: John Stultz <john.stultz@linaro.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: "Serge E. Hallyn" <serge@hallyn.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Arjan van de Ven <arjan@linux.intel.com>
> Cc: Oren Laadan <orenl@cellrox.com>
> Cc: Ruchi Kandoi <kandoiruchi@google.com>
> Cc: Rom Lemarchand <romlem@android.com>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: Colin Cross <ccross@android.com>
> Cc: Nick Kralevich <nnk@google.com>
> Cc: Dmitry Shmidt <dimitrysh@google.com>
> Cc: Elliott Hughes <enh@google.com>
> Cc: Android Kernel Team <kernel-team@android.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> ---
>  fs/proc/base.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 7e9f07bf260d..4b50937dff80 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2356,7 +2356,7 @@ static ssize_t timerslack_ns_write(struct file *file, const char __user *buf,
>                 return -ESRCH;
>
>         if (p != current) {
> -               if (!capable(CAP_SYS_NICE)) {
> +               if (!ns_capable(file->f_cred->user_ns, CAP_SYS_NICE)) {
>                         count = -EPERM;
>                         goto out;
>                 }
> @@ -2393,7 +2393,7 @@ static int timerslack_ns_show(struct seq_file *m, void *v)
>
>         if (p != current) {
>
> -               if (!capable(CAP_SYS_NICE)) {
> +               if (!ns_capable(seq_user_ns(m), CAP_SYS_NICE)) {
>                         err = -EPERM;
>                         goto out;
>                 }

Looks reasonable to me.
Acked-by: John Stultz <john.stultz@linaro.org>

thanks
-john

Re: [PATCH] proc: use ns_capable instead of capable for timerslack_ns

[Eric W. Biederman]

bmgordon@google.com writes:

> From: Benjamin Gordon <bmgordon@google.com>
>
> Access to timerslack_ns is controlled by a process having CAP_SYS_NICE
> in its effective capability set, but the current check looks in the root
> namespace instead of the process' user namespace.  Since a process is
> allowed to do other activities controlled by CAP_SYS_NICE inside a
> namespace, it should also be able to adjust timerslack_ns.

The goal seems legitimate.  However the permission checks look wrong.

In particular the choice of user namespace should be
"p->cred->user_ns".  This will limit this to tasks that have
CAP_SYS_NICE in the same namespace as the task that is being modified.

Testing file->f_cred->user_ns it is testing whoever opened the file and
that could be anyone.

Eric


> Signed-off-by: Benjamin Gordon <bmgordon@google.com>
> Cc: John Stultz <john.stultz@linaro.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: "Serge E. Hallyn" <serge@hallyn.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Arjan van de Ven <arjan@linux.intel.com>
> Cc: Oren Laadan <orenl@cellrox.com>
> Cc: Ruchi Kandoi <kandoiruchi@google.com>
> Cc: Rom Lemarchand <romlem@android.com>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: Colin Cross <ccross@android.com>
> Cc: Nick Kralevich <nnk@google.com>
> Cc: Dmitry Shmidt <dimitrysh@google.com>
> Cc: Elliott Hughes <enh@google.com>
> Cc: Android Kernel Team <kernel-team@android.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> ---
>  fs/proc/base.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 7e9f07bf260d..4b50937dff80 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2356,7 +2356,7 @@ static ssize_t timerslack_ns_write(struct file *file, const char __user *buf,
>  		return -ESRCH;
>  
>  	if (p != current) {
> -		if (!capable(CAP_SYS_NICE)) {
> +		if (!ns_capable(file->f_cred->user_ns, CAP_SYS_NICE)) {
>  			count = -EPERM;
>  			goto out;
>  		}
> @@ -2393,7 +2393,7 @@ static int timerslack_ns_show(struct seq_file *m, void *v)
>  
>  	if (p != current) {
>  
> -		if (!capable(CAP_SYS_NICE)) {
> +		if (!ns_capable(seq_user_ns(m), CAP_SYS_NICE)) {
>  			err = -EPERM;
>  			goto out;
>  		}

Re: [PATCH] proc: use ns_capable instead of capable for timerslack_ns

[Benjamin Gordon]

On Thu, Oct 25, 2018 at 01:56:27PM -0500, Eric W. Biederman wrote:
> > Access to timerslack_ns is controlled by a process having CAP_SYS_NICE
> > in its effective capability set, but the current check looks in the root
> > namespace instead of the process' user namespace.  Since a process is
> > allowed to do other activities controlled by CAP_SYS_NICE inside a
> > namespace, it should also be able to adjust timerslack_ns.
> 
> The goal seems legitimate.  However the permission checks look wrong.
> 
> In particular the choice of user namespace should be
> "p->cred->user_ns".  This will limit this to tasks that have
> CAP_SYS_NICE in the same namespace as the task that is being modified.
> 
> Testing file->f_cred->user_ns it is testing whoever opened the file and
> that could be anyone.

Thanks, that seems like the right answer here.  I'll send a v2 to fix
it.

Thanks,
Benjamin