[RFC PATCH 1/2] security, capabilities: create CAP_TRUSTED

[RFC PATCH 1/2] security, capabilities: create CAP_TRUSTED

[Nicolas Belouin]

with CAP_SYS_ADMIN being bloated, the usefulness of using it to
flag a process to be entrusted for e.g reading and writing trusted
xattr is near zero.
CAP_TRUSTED aims to provide userland with a way to mark a process as
entrusted to do specific (not specially admin-centered) actions. It
would for example allow a process to red/write the trusted xattrs.

Signed-off-by: Nicolas Belouin <nicolas@belouin.fr>
---
 include/uapi/linux/capability.h     | 6 +++++-
 security/selinux/include/classmap.h | 5 +++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
index ce230aa6d928..27e457b93c84 100644
--- a/include/uapi/linux/capability.h
+++ b/include/uapi/linux/capability.h
@@ -369,7 +369,11 @@ struct vfs_ns_cap_data {
 
 #define CAP_SYS_MOUNT		38
 
-#define CAP_LAST_CAP         CAP_SYS_MOUNT
+/* Allow read/write trusted xattr */
+
+#define CAP_TRUSTED		39
+
+#define CAP_LAST_CAP         CAP_TRUSTED
 
 #define cap_valid(x) ((x) >= 0 && (x) <= CAP_LAST_CAP)
 
diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
index a873dce97fd5..f5dc8e109f5a 100644
--- a/security/selinux/include/classmap.h
+++ b/security/selinux/include/classmap.h
@@ -24,9 +24,10 @@
 	    "audit_control", "setfcap"
 
 #define COMMON_CAP2_PERMS  "mac_override", "mac_admin", "syslog", \
-		"wake_alarm", "block_suspend", "audit_read", "sys_mount"
+		"wake_alarm", "block_suspend", "audit_read", "sys_mount", \
+		"trusted"
 
-#if CAP_LAST_CAP > CAP_SYS_MOUNT
+#if CAP_LAST_CAP > CAP_TRUSTED
 #error New capability defined, please update COMMON_CAP2_PERMS.
 #endif
 
-- 
2.14.2

[RFC PATCH 2/2] fs: Grant CAP_TRUSTED rw access to trusted xattrs

[Nicolas Belouin]

The trusted xattrs read/write access is the perfect use case for
CAP_TRUSTED.

Signed-off-by: Nicolas Belouin <nicolas@belouin.fr>
---
 fs/ext2/xattr_trusted.c     |  2 +-
 fs/ext4/xattr_trusted.c     |  2 +-
 fs/f2fs/xattr.c             |  6 +++---
 fs/hfsplus/xattr.c          |  2 +-
 fs/jffs2/xattr_trusted.c    |  2 +-
 fs/jfs/xattr.c              |  3 ++-
 fs/ocfs2/xattr.c            |  2 +-
 fs/overlayfs/inode.c        |  3 ++-
 fs/reiserfs/xattr_trusted.c | 11 ++++++++---
 fs/squashfs/xattr.c         |  2 +-
 fs/ubifs/xattr.c            |  3 ++-
 fs/xattr.c                  |  4 ++--
 12 files changed, 25 insertions(+), 17 deletions(-)

diff --git a/fs/ext2/xattr_trusted.c b/fs/ext2/xattr_trusted.c
index 65049b71af13..8006c24f8ee0 100644
--- a/fs/ext2/xattr_trusted.c
+++ b/fs/ext2/xattr_trusted.c
@@ -11,7 +11,7 @@
 static bool
 ext2_xattr_trusted_list(struct dentry *dentry)
 {
-	return capable(CAP_SYS_ADMIN);
+	return capable(CAP_SYS_ADMIN) || capable(CAP_TRUSTED);
 }
 
 static int
diff --git a/fs/ext4/xattr_trusted.c b/fs/ext4/xattr_trusted.c
index c7765c735714..9849d1e0ebb9 100644
--- a/fs/ext4/xattr_trusted.c
+++ b/fs/ext4/xattr_trusted.c
@@ -15,7 +15,7 @@
 static bool
 ext4_xattr_trusted_list(struct dentry *dentry)
 {
-	return capable(CAP_SYS_ADMIN);
+	return capable(CAP_SYS_ADMIN) || capable(CAP_TRUSTED);
 }
 
 static int
diff --git a/fs/f2fs/xattr.c b/fs/f2fs/xattr.c
index 7c65540148f8..ef572464deca 100644
--- a/fs/f2fs/xattr.c
+++ b/fs/f2fs/xattr.c
@@ -37,7 +37,7 @@ static int f2fs_xattr_generic_get(const struct xattr_handler *handler,
 			return -EOPNOTSUPP;
 		break;
 	case F2FS_XATTR_INDEX_TRUSTED:
-		if (!capable(CAP_SYS_ADMIN))
+		if (!capable(CAP_SYS_ADMIN) && !capable(CAP_TRUSTED))
 			return -EPERM;
 		break;
 	case F2FS_XATTR_INDEX_SECURITY:
@@ -62,7 +62,7 @@ static int f2fs_xattr_generic_set(const struct xattr_handler *handler,
 			return -EOPNOTSUPP;
 		break;
 	case F2FS_XATTR_INDEX_TRUSTED:
-		if (!capable(CAP_SYS_ADMIN))
+		if (!capable(CAP_SYS_ADMIN) && !capable(CAP_TRUSTED))
 			return -EPERM;
 		break;
 	case F2FS_XATTR_INDEX_SECURITY:
@@ -83,7 +83,7 @@ static bool f2fs_xattr_user_list(struct dentry *dentry)
 
 static bool f2fs_xattr_trusted_list(struct dentry *dentry)
 {
-	return capable(CAP_SYS_ADMIN);
+	return capable(CAP_SYS_ADMIN) || capable(CAP_TRUSTED);
 }
 
 static int f2fs_xattr_advise_get(const struct xattr_handler *handler,
diff --git a/fs/hfsplus/xattr.c b/fs/hfsplus/xattr.c
index ae03a19196ef..0ec6d02ee7e9 100644
--- a/fs/hfsplus/xattr.c
+++ b/fs/hfsplus/xattr.c
@@ -606,7 +606,7 @@ static inline int can_list(const char *xattr_name)
 
 	return !strncmp(xattr_name, XATTR_TRUSTED_PREFIX,
 			XATTR_TRUSTED_PREFIX_LEN) ||
-				capable(CAP_SYS_ADMIN);
+				capable(CAP_SYS_ADMIN) || capable(CAP_TRUSTED);
 }
 
 static ssize_t hfsplus_listxattr_finder_info(struct dentry *dentry,
diff --git a/fs/jffs2/xattr_trusted.c b/fs/jffs2/xattr_trusted.c
index 5d6030826c52..3c7ae98e4525 100644
--- a/fs/jffs2/xattr_trusted.c
+++ b/fs/jffs2/xattr_trusted.c
@@ -35,7 +35,7 @@ static int jffs2_trusted_setxattr(const struct xattr_handler *handler,
 
 static bool jffs2_trusted_listxattr(struct dentry *dentry)
 {
-	return capable(CAP_SYS_ADMIN);
+	return capable(CAP_SYS_ADMIN) || capable(CAP_TRUSTED);
 }
 
 const struct xattr_handler jffs2_trusted_xattr_handler = {
diff --git a/fs/jfs/xattr.c b/fs/jfs/xattr.c
index 1c46573a96ed..e4f44f5133a1 100644
--- a/fs/jfs/xattr.c
+++ b/fs/jfs/xattr.c
@@ -859,7 +859,8 @@ ssize_t __jfs_getxattr(struct inode *inode, const char *name, void *data,
 static inline int can_list(struct jfs_ea *ea)
 {
 	return (!strncmp(ea->name, XATTR_TRUSTED_PREFIX,
-			 XATTR_TRUSTED_PREFIX_LEN) || capable(CAP_SYS_ADMIN));
+			 XATTR_TRUSTED_PREFIX_LEN) ||
+		capable(CAP_SYS_ADMIN) || capable(CAP_TRUSTED));
 }
 
 ssize_t jfs_listxattr(struct dentry * dentry, char *data, size_t buf_size)
diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
index 5fdf269ba82e..2b3994d192c6 100644
--- a/fs/ocfs2/xattr.c
+++ b/fs/ocfs2/xattr.c
@@ -906,7 +906,7 @@ static int ocfs2_xattr_list_entry(struct super_block *sb,
 		break;
 
 	case OCFS2_XATTR_INDEX_TRUSTED:
-		if (!capable(CAP_SYS_ADMIN))
+		if (!capable(CAP_SYS_ADMIN) && !capable(CAP_TRUSTED))
 			return 0;
 		break;
 	}
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index a619addecafc..c627003d3a74 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -264,7 +264,8 @@ static bool ovl_can_list(const char *s)
 		return true;
 
 	/* Never list trusted.overlay, list other trusted for superuser only */
-	return !ovl_is_private_xattr(s) && capable(CAP_SYS_ADMIN);
+	return !ovl_is_private_xattr(s) &&
+		(capable(CAP_SYS_ADMIN) || capable(CAP_TRUSTED));
 }
 
 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
diff --git a/fs/reiserfs/xattr_trusted.c b/fs/reiserfs/xattr_trusted.c
index f15a5f9e84ce..6f3fa0db8272 100644
--- a/fs/reiserfs/xattr_trusted.c
+++ b/fs/reiserfs/xattr_trusted.c
@@ -7,11 +7,16 @@
 #include "xattr.h"
 #include <linux/uaccess.h>
 
+inline bool trusted_capable(void)
+{
+	return capable(CAP_SYS_ADMIN) || capable(CAP_TRUSTED);
+}
+
 static int
 trusted_get(const struct xattr_handler *handler, struct dentry *unused,
 	    struct inode *inode, const char *name, void *buffer, size_t size)
 {
-	if (!capable(CAP_SYS_ADMIN) || IS_PRIVATE(inode))
+	if (!trusted_capable() || IS_PRIVATE(inode))
 		return -EPERM;
 
 	return reiserfs_xattr_get(inode, xattr_full_name(handler, name),
@@ -23,7 +28,7 @@ trusted_set(const struct xattr_handler *handler, struct dentry *unused,
 	    struct inode *inode, const char *name, const void *buffer,
 	    size_t size, int flags)
 {
-	if (!capable(CAP_SYS_ADMIN) || IS_PRIVATE(inode))
+	if (!trusted_capable() || IS_PRIVATE(inode))
 		return -EPERM;
 
 	return reiserfs_xattr_set(inode,
@@ -33,7 +38,7 @@ trusted_set(const struct xattr_handler *handler, struct dentry *unused,
 
 static bool trusted_list(struct dentry *dentry)
 {
-	return capable(CAP_SYS_ADMIN) && !IS_PRIVATE(d_inode(dentry));
+	return trusted_capable() && !IS_PRIVATE(d_inode(dentry));
 }
 
 const struct xattr_handler reiserfs_xattr_trusted_handler = {
diff --git a/fs/squashfs/xattr.c b/fs/squashfs/xattr.c
index 1548b3784548..e0a285ab1f7e 100644
--- a/fs/squashfs/xattr.c
+++ b/fs/squashfs/xattr.c
@@ -237,7 +237,7 @@ static const struct xattr_handler squashfs_xattr_user_handler = {
  */
 static bool squashfs_trusted_xattr_handler_list(struct dentry *d)
 {
-	return capable(CAP_SYS_ADMIN);
+	return capable(CAP_SYS_ADMIN) || capable(CAP_TRUSTED);
 }
 
 static const struct xattr_handler squashfs_xattr_trusted_handler = {
diff --git a/fs/ubifs/xattr.c b/fs/ubifs/xattr.c
index c13eae819cbc..f3aa8be72a66 100644
--- a/fs/ubifs/xattr.c
+++ b/fs/ubifs/xattr.c
@@ -406,7 +406,8 @@ static bool xattr_visible(const char *name)
 
 	/* Show trusted namespace only for "power" users */
 	if (strncmp(name, XATTR_TRUSTED_PREFIX,
-		    XATTR_TRUSTED_PREFIX_LEN) == 0 && !capable(CAP_SYS_ADMIN))
+		    XATTR_TRUSTED_PREFIX_LEN) == 0 &&
+	    !capable(CAP_SYS_ADMIN) && !capable(CAP_TRUSTED))
 		return false;
 
 	return true;
diff --git a/fs/xattr.c b/fs/xattr.c
index 61cd28ba25f3..d9e9a0083dbb 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -113,7 +113,7 @@ xattr_permission(struct inode *inode, const char *name, int mask)
 	 * The trusted.* namespace can only be accessed by privileged users.
 	 */
 	if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN)) {
-		if (!capable(CAP_SYS_ADMIN))
+		if (!capable(CAP_SYS_ADMIN) && !capable(CAP_TRUSTED))
 			return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
 		return 0;
 	}
@@ -945,7 +945,7 @@ static int xattr_list_one(char **buffer, ssize_t *remaining_size,
 ssize_t simple_xattr_list(struct inode *inode, struct simple_xattrs *xattrs,
 			  char *buffer, size_t size)
 {
-	bool trusted = capable(CAP_SYS_ADMIN);
+	bool trusted = capable(CAP_SYS_ADMIN) || capable(CAP_TRUSTED);
 	struct simple_xattr *xattr;
 	ssize_t remaining_size = size;
 	int err = 0;
-- 
2.14.2

Re: [RFC PATCH 1/2] security, capabilities: create CAP_TRUSTED

[Serge E. Hallyn]

Quoting Nicolas Belouin (nicolas@belouin.fr):
> with CAP_SYS_ADMIN being bloated, the usefulness of using it to
> flag a process to be entrusted for e.g reading and writing trusted
> xattr is near zero.
> CAP_TRUSTED aims to provide userland with a way to mark a process as
> entrusted to do specific (not specially admin-centered) actions. It
> would for example allow a process to red/write the trusted xattrs.

You say "for example".  Are you intending to add more uses?  If so, what
are they?  If not, how about renaming it CAP_TRUSTED_XATTR?

What all does allowing writes to trusted xattrs give you?  There are
the overlayfs whiteouts, what else?

Re: [kernel-hardening] [RFC PATCH 1/2] security, capabilities: create CAP_TRUSTED

[Casey Schaufler]

On 10/21/2017 6:45 AM, Nicolas Belouin wrote:
> with CAP_SYS_ADMIN being bloated, the usefulness of using it to
> flag a process to be entrusted for e.g reading and writing trusted
> xattr is near zero.
> CAP_TRUSTED aims to provide userland with a way to mark a process as
> entrusted to do specific (not specially admin-centered) actions. It
> would for example allow a process to red/write the trusted xattrs.

Please explain how this is different from CAP_MAC_ADMIN in
any existing use case. If it is significantly different, how
would the two interact?

> Signed-off-by: Nicolas Belouin <nicolas@belouin.fr>
> ---
>  include/uapi/linux/capability.h     | 6 +++++-
>  security/selinux/include/classmap.h | 5 +++--
>  2 files changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
> index ce230aa6d928..27e457b93c84 100644
> --- a/include/uapi/linux/capability.h
> +++ b/include/uapi/linux/capability.h
> @@ -369,7 +369,11 @@ struct vfs_ns_cap_data {
>  
>  #define CAP_SYS_MOUNT		38
>  
> -#define CAP_LAST_CAP         CAP_SYS_MOUNT
> +/* Allow read/write trusted xattr */
> +
> +#define CAP_TRUSTED		39
> +
> +#define CAP_LAST_CAP         CAP_TRUSTED
>  
>  #define cap_valid(x) ((x) >= 0 && (x) <= CAP_LAST_CAP)
>  
> diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
> index a873dce97fd5..f5dc8e109f5a 100644
> --- a/security/selinux/include/classmap.h
> +++ b/security/selinux/include/classmap.h
> @@ -24,9 +24,10 @@
>  	    "audit_control", "setfcap"
>  
>  #define COMMON_CAP2_PERMS  "mac_override", "mac_admin", "syslog", \
> -		"wake_alarm", "block_suspend", "audit_read", "sys_mount"
> +		"wake_alarm", "block_suspend", "audit_read", "sys_mount", \
> +		"trusted"
>  
> -#if CAP_LAST_CAP > CAP_SYS_MOUNT
> +#if CAP_LAST_CAP > CAP_TRUSTED
>  #error New capability defined, please update COMMON_CAP2_PERMS.
>  #endif
>  

Re: [kernel-hardening] [RFC PATCH 1/2] security, capabilities: create CAP_TRUSTED

[nicolas]

<james.l.morris@oracle.com>,linux-ext4@vger.kernel.org,linux-kernel@vger.kernel.org,linux-f2fs-devel@lists.sourceforge.net,linux-fsdevel@vger.kernel.org,linux-mtd@lists.infradead.org,jfs-discussion@lists.sourceforge.net,ocfs2-devel@oss.oracle.com,linux-unionfs@vger.kernel.org,reiserfs-devel@vger.kernel.org,linux-security-module@vger.kernel.org,selinux@tycho.nsa.gov,linux-api@vger.kernel.org,kernel-hardening@lists.openwall.com
From: Nicolas Belouin <nicolas@belouin.fr>
Message-ID: <E5A1BDA4-A309-4118-84D5-72780F619EBA@belouin.fr>



On October 21, 2017 7:25:21 PM GMT+02:00, Casey Schaufler <casey@schaufler-ca.com> wrote:
>On 10/21/2017 6:45 AM, Nicolas Belouin wrote:
>> with CAP_SYS_ADMIN being bloated, the usefulness of using it to
>> flag a process to be entrusted for e.g reading and writing trusted
>> xattr is near zero.
>> CAP_TRUSTED aims to provide userland with a way to mark a process as
>> entrusted to do specific (not specially admin-centered) actions. It
>> would for example allow a process to red/write the trusted xattrs.
>
>Please explain how this is different from CAP_MAC_ADMIN in
>any existing use case. If it is significantly different, how
>would the two interact?

>From my point of view, CAP_MAC_ADMIN allows one to read/write security xattrs, those are meant to describe security policies. As far as I know of, trusted xattrs are intended for a privileged process to read or write arbitrary data. I don't have any real world example in mind that use trusted xattrs, but I'll try to find one.

>
>> Signed-off-by: Nicolas Belouin <nicolas@belouin.fr>
>> ---
>>  include/uapi/linux/capability.h     | 6 +++++-
>>  security/selinux/include/classmap.h | 5 +++--
>>  2 files changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/uapi/linux/capability.h
>b/include/uapi/linux/capability.h
>> index ce230aa6d928..27e457b93c84 100644
>> --- a/include/uapi/linux/capability.h
>> +++ b/include/uapi/linux/capability.h
>> @@ -369,7 +369,11 @@ struct vfs_ns_cap_data {
>>  
>>  #define CAP_SYS_MOUNT		38
>>  
>> -#define CAP_LAST_CAP         CAP_SYS_MOUNT
>> +/* Allow read/write trusted xattr */
>> +
>> +#define CAP_TRUSTED		39
>> +
>> +#define CAP_LAST_CAP         CAP_TRUSTED
>>  
>>  #define cap_valid(x) ((x) >= 0 && (x) <= CAP_LAST_CAP)
>>  
>> diff --git a/security/selinux/include/classmap.h
>b/security/selinux/include/classmap.h
>> index a873dce97fd5..f5dc8e109f5a 100644
>> --- a/security/selinux/include/classmap.h
>> +++ b/security/selinux/include/classmap.h
>> @@ -24,9 +24,10 @@
>>  	    "audit_control", "setfcap"
>>  
>>  #define COMMON_CAP2_PERMS  "mac_override", "mac_admin", "syslog", \
>> -		"wake_alarm", "block_suspend", "audit_read", "sys_mount"
>> +		"wake_alarm", "block_suspend", "audit_read", "sys_mount", \
>> +		"trusted"
>>  
>> -#if CAP_LAST_CAP > CAP_SYS_MOUNT
>> +#if CAP_LAST_CAP > CAP_TRUSTED
>>  #error New capability defined, please update COMMON_CAP2_PERMS.
>>  #endif
>>  

Nicolas

Re: [RFC PATCH 1/2] security, capabilities: create CAP_TRUSTED

[nicolas]

<james.l.morris@oracle.com>,linux-ext4@vger.kernel.org,linux-kernel@vger.kernel.org,linux-f2fs-devel@lists.sourceforge.net,linux-fsdevel@vger.kernel.org,linux-mtd@lists.infradead.org,jfs-discussion@lists.sourceforge.net,ocfs2-devel@oss.oracle.com,linux-unionfs@vger.kernel.org,reiserfs-devel@vger.kernel.org,linux-security-module@vger.kernel.org,selinux@tycho.nsa.gov,linux-api@vger.kernel.org,kernel-hardening@lists.openwall.com
From: Nicolas Belouin <nicolas@belouin.fr>
Message-ID: <99179B10-4EAE-4FAB-9D14-B885156261B3@belouin.fr>



On October 21, 2017 6:03:02 PM GMT+02:00, "Serge E. Hallyn" <serge@hallyn.com> wrote:
>Quoting Nicolas Belouin (nicolas@belouin.fr):
>> with CAP_SYS_ADMIN being bloated, the usefulness of using it to
>> flag a process to be entrusted for e.g reading and writing trusted
>> xattr is near zero.
>> CAP_TRUSTED aims to provide userland with a way to mark a process as
>> entrusted to do specific (not specially admin-centered) actions. It
>> would for example allow a process to red/write the trusted xattrs.
>
>You say "for example".  Are you intending to add more uses?  If so,
>what
>are they?  If not, how about renaming it CAP_TRUSTED_XATTR?
>

I don't see any other use for now, but I don't want it to be too narrow and non usable in a similar context in the future. So I believe the underlying purpose of marking a process as "trusted" (even if for now it only means rw permission on trusted xattr) is more meaningful.

>What all does allowing writes to trusted xattrs give you?  There are
>the overlayfs whiteouts, what else?

Nicolas