Introduce is_owner_or_cap() to wrap CAP_FOWNER use with fsuid check

Introduce is_owner_or_cap() macro in fs.h, and convert over relevant
users to it. This is done because we want to avoid bugs in the future
where we check for only effective fsuid of the current task against a
file's owning uid, without simultaneously checking for CAP_FOWNER as
well, thus violating its semantics.
[ XFS uses special macros and structures, and in general looked ...
untouchable, so we leave it alone -- but it has been looked over. ]

The (current->fsuid != inode->i_uid) check in generic_permission() and
exec_permission_lite() is left alone, because those operations are
covered by CAP_DAC_OVERRIDE and CAP_DAC_READ_SEARCH. Similarly operations
falling under the purview of CAP_CHOWN and CAP_LEASE are also left alone.

Signed-off-by: Satyam Sharma <ssatyam@cse.iitk.ac.in>
Cc: Al Viro <viro@ftp.linux.org.uk>
Acked-by: Serge E. Hallyn <serge@hallyn.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 2 insertions, 2 deletions

diff --git a/fs/jfs/ioctl.c b/fs/jfs/ioctl.c
index fe063af6fd2f..3c8663bea98c 100644
--- a/fs/jfs/ioctl.c
+++ b/fs/jfs/ioctl.c
@@ -69,7 +69,7 @@ int jfs_ioctl(struct inode * inode, struct file * filp, unsigned int cmd,
                 if (IS_RDONLY(inode))
                         return -EROFS;
 
-                if ((current->fsuid != inode->i_uid) && !capable(CAP_FOWNER))
+                if (!is_owner_or_cap(inode))
                         return -EACCES;
 
                 if (get_user(flags, (int __user *) arg))
diff --git a/fs/jfs/xattr.c b/fs/jfs/xattr.c
index b2375f0774b7..9b7f2cdaae0a 100644
--- a/fs/jfs/xattr.c
+++ b/fs/jfs/xattr.c
@@ -697,7 +697,7 @@ static int can_set_system_xattr(struct inode *inode, const char *name,
         struct posix_acl *acl;
         int rc;
 
-        if ((current->fsuid != inode->i_uid) && !capable(CAP_FOWNER))
+        if (!is_owner_or_cap(inode))
                 return -EPERM;
 
         /*