fanotify: do not dereference inode_mark when it is unset

The fanotify code is supposed to get the group from the mark.  It accidentally
only used the inode_mark.  If the vfsmount_mark was set but not the inode_mark
it would deref the NULL inode_mark.  Get the group from the correct place.

Reported-by: Tvrtko Ursulin <tvrtko.ursulin@sophos.com>
Signed-off-by: Eric Paris <eparis@redhat.com>

1 files changed, 11 insertions, 4 deletions

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 3970392b2722..f3e3b355ba7f 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -148,13 +148,14 @@ static int send_to_group(struct inode *to_tell, struct vfsmount *mnt,
                          const unsigned char *file_name,
                          struct fsnotify_event **event)
 {
-        struct fsnotify_group *group = inode_mark->group;
+        struct fsnotify_group *group = NULL;
         __u32 inode_test_mask = (mask & ~FS_EVENT_ON_CHILD);
         __u32 vfsmount_test_mask = (mask & ~FS_EVENT_ON_CHILD);
 
-        pr_debug("%s: group=%p to_tell=%p mnt=%p mark=%p mask=%x data=%p"
-                 " data_is=%d cookie=%d event=%p\n", __func__, group, to_tell,
-                 mnt, inode_mark, mask, data, data_is, cookie, *event);
+        if (unlikely(!inode_mark && !vfsmount_mark)) {
+                BUG();
+                return 0;
+        }
 
         /* clear ignored on inode modification */
         if (mask & FS_MODIFY) {
@@ -168,18 +169,24 @@ static int send_to_group(struct inode *to_tell, struct vfsmount *mnt,
 
         /* does the inode mark tell us to do something? */
         if (inode_mark) {
+                group = inode_mark->group;
                 inode_test_mask &= inode_mark->mask;
                 inode_test_mask &= ~inode_mark->ignored_mask;
         }
 
         /* does the vfsmount_mark tell us to do something? */
         if (vfsmount_mark) {
+                group = vfsmount_mark->group;
                 vfsmount_test_mask &= vfsmount_mark->mask;
                 vfsmount_test_mask &= ~vfsmount_mark->ignored_mask;
                 if (inode_mark)
                         vfsmount_test_mask &= ~inode_mark->ignored_mask;
         }
 
+        pr_debug("%s: group=%p to_tell=%p mnt=%p mark=%p mask=%x data=%p"
+                 " data_is=%d cookie=%d event=%p\n", __func__, group, to_tell,
+                 mnt, inode_mark, mask, data, data_is, cookie, *event);
+
         if (!inode_test_mask && !vfsmount_test_mask)
                 return 0;