fanotify: Fix stale file descriptor in copy_event_to_user()
authorDan Carpenter <dan.carpenter@oracle.com>
Fri, 28 Jan 2022 19:57:01 +0000 (22:57 +0300)
committerJan Kara <jack@suse.cz>
Tue, 1 Feb 2022 11:52:07 +0000 (12:52 +0100)
commitee12595147ac1fbfb5bcb23837e26dd58d94b15d
tree23b335c261ec5a532107c5c69fe95348bd57db83
parent26291c54e111ff6ba87a164d85d4a4e134b7315c
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")
Link: https://lore.kernel.org/r/20220128195656.GA26981@kili
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Mathias Krause <minipli@grsecurity.net>
Signed-off-by: Jan Kara <jack@suse.cz>
fs/notify/fanotify/fanotify_user.c