Abort file_remove_privs() for non-reg. files

BugLink: https://bugs.launchpad.net/bugs/1838824
commit f69e749a49353d96af1a293f56b5b56de59c668a upstream.

file_remove_privs() might be called for non-regular files, e.g.
blkdev inode. There is no reason to do its job on things
like blkdev inodes, pipes, or cdevs. Hence, abort if
file does not refer to a regular inode.

AV: more to the point, for devices there might be any number of
inodes refering to given device.  Which one to strip the permissions
from, even if that made any sense in the first place?  All of them
will be observed with contents modified, after all.

Found by LockDoc (Alexander Lochmann, Horst Schirmeier and Olaf
Spinczyk)

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Alexander Lochmann <alexander.lochmann@tu-dortmund.de>
Signed-off-by: Horst Schirmeier <horst.schirmeier@tu-dortmund.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Zubin Mithra <zsm@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/fs/inode.c b/fs/inode.c
index 7de7df08fe48422c726a39d761cbc399ad35d4eb..b7841b4f2bd05b1b86c10cf2aed70b4b64e2797b 100644 (file)
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1820,8 +1820,13 @@ int file_remove_privs(struct file *file)
        int kill;
        int error = 0;
 
-       /* Fast path for nothing security related */
-       if (IS_NOSEC(inode))
+       /*
+        * Fast path for nothing security related.
+        * As well for non-regular files, e.g. blkdev inodes.
+        * For example, blkdev_write_iter() might get here
+        * trying to remove privs which it is not allowed to.
+        */
+       if (IS_NOSEC(inode) || !S_ISREG(inode->i_mode))
                return 0;
 
        kill = dentry_needs_remove_privs(dentry);