[PATCH] fanotify: fix logic of events on child

[Amir Goldstein <amir73il@xxxxxxxxx>]

When event on child inodes are sent to the parent inode mark and
parent inode mark was not marked with FAN_EVENT_ON_CHILD, the event
will not be delivered to the listener process. However, if the same
process also has a mount mark, the event to the parent inode will be
delivered regadless of the mount mark mask.

This behavior is incorrect in the case where the mount mark mask does
not contain the specific event type. For example, the process adds
a mark on a directory with mask FAN_MODIFY (without FAN_EVENT_ON_CHILD)
and a mount mark with mask FAN_CLOSE_NOWRITE (without FAN_ONDIR).

A modify event on a file inside that directory (and inside that mount)
should not create a FAN_MODIFY event, because neither of the marks
requested to get that event on the file.

Fixes: 1968f5eed54c ("fanotify: use both marks when possible")
Cc: stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
 fs/notify/fanotify/fanotify.c | 34 +++++++++++++++-------------------
 1 file changed, 15 insertions(+), 19 deletions(-)

Jan,

While working on the super block mark patches [1], I stumbbled on
this bug. I figured I might as well send the fix out now.

I have written an LTP test [2] to reproduce it.

Thanks,
Amir.

[1] https://github.com/amir73il/linux/commits/fanotify_sb
[2] https://github.com/amir73il/ltp/commits/fanotify_sb

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 6702a6a0bbb5..e0e6a9d627df 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -92,7 +92,7 @@ static bool fanotify_should_send_event(struct fsnotify_mark *inode_mark,
 				       u32 event_mask,
 				       const void *data, int data_type)
 {
-	__u32 marks_mask, marks_ignored_mask;
+	__u32 marks_mask = 0, marks_ignored_mask = 0;
 	const struct path *path = data;
 
 	pr_debug("%s: inode_mark=%p vfsmnt_mark=%p mask=%x data=%p"
@@ -108,24 +108,20 @@ static bool fanotify_should_send_event(struct fsnotify_mark *inode_mark,
 	    !d_can_lookup(path->dentry))
 		return false;
 
-	if (inode_mark && vfsmnt_mark) {
-		marks_mask = (vfsmnt_mark->mask | inode_mark->mask);
-		marks_ignored_mask = (vfsmnt_mark->ignored_mask | inode_mark->ignored_mask);
-	} else if (inode_mark) {
-		/*
-		 * if the event is for a child and this inode doesn't care about
-		 * events on the child, don't send it!
-		 */
-		if ((event_mask & FS_EVENT_ON_CHILD) &&
-		    !(inode_mark->mask & FS_EVENT_ON_CHILD))
-			return false;
-		marks_mask = inode_mark->mask;
-		marks_ignored_mask = inode_mark->ignored_mask;
-	} else if (vfsmnt_mark) {
-		marks_mask = vfsmnt_mark->mask;
-		marks_ignored_mask = vfsmnt_mark->ignored_mask;
-	} else {
-		BUG();
+	/*
+	 * if the event is for a child and this inode doesn't care about
+	 * events on the child, don't send it!
+	 */
+	if (inode_mark &&
+	    (!(event_mask & FS_EVENT_ON_CHILD) ||
+	     (inode_mark->mask & FS_EVENT_ON_CHILD))) {
+		marks_mask |= inode_mark->mask;
+		marks_ignored_mask |= inode_mark->ignored_mask;
+	}
+
+	if (vfsmnt_mark) {
+		marks_mask |= vfsmnt_mark->mask;
+		marks_ignored_mask |= vfsmnt_mark->ignored_mask;
 	}
 
 	if (d_is_dir(path->dentry) &&
-- 
2.7.4