fanotify: if set by user unset FMODE_NONOTIFY before fsnotify_perm() is called

Unsetting FMODE_NONOTIFY in fsnotify_open() is too late, since fsnotify_perm()
is called before. If FMODE_NONOTIFY is set fsnotify_perm() will skip permission
checks, so a user can still disable permission checks by setting this flag
in an open() call.
This patch corrects this by unsetting the flag before fsnotify_perm is called.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: Eric Paris <eparis@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 5362af9b7372..4ff7ca530533 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1748,6 +1748,9 @@ struct file *do_filp_open(int dfd, const char *pathname,
         if (!(open_flag & O_CREAT))
                 mode = 0;
 
+        /* Must never be set by userspace */
+        open_flag &= ~FMODE_NONOTIFY;
+
         /*
          * O_SYNC is implemented as __O_SYNC|O_DSYNC.  As many places only
          * check for O_DSYNC if the need any syncing at all we enforce it's