fanotify: Fix stale file descriptor in copy_event_to_user()

This code calls fd_install() which gives the userspace access to the fd. Then if copy_info_records_to_user() fails it calls put_unused_fd(fd) but that will not release it and leads to a stale entry in the file descriptor table.

Generally you can't trust the fd after a call to fd_install(). The fix is to delay the fd_install() until everything else has succeeded.

Fortunately it requires CAP_SYS_ADMIN to reach this code so the security impact is less.

Fixes f644bc449b37 ("fanotify: fix copy_event_to_user() fid error clean up")

Signed-off-by Dan Carpenter <[email protected]>

Reviewed-by Mathias Krause <[email protected]>

---
 fs/notify/fanotify/fanotify_user.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

fs/notify/fanotify/fanotify_user.c +3 -3

index 1026f67b1d1e..2ff6bd85ba8f 100644
@@ -701,9 +701,6 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
 	if (fanotify_is_perm_event(event->mask))
 		FANOTIFY_PERM(event)->fd = fd;
 
-	if (f)
-		fd_install(fd, f);
-
 	if (info_mode) {
 		ret = copy_info_records_to_user(event, info, info_mode, pidfd,
 						buf, count);

@@ -711,6 +708,9 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
 			goto out_close_fd;
 	}
 
+	if (f)
+		fd_install(fd, f);
+
 	return metadata.event_len;
 
 out_close_fd:

Signature · 1 line

2.20.1