From ee12595147ac1fbfb5bcb23837e26dd58d94b15d Mon Sep 17 00:00:00 2001
From: Dan Carpenter <dan.carpenter@oracle.com>
Date: Fri, 28 Jan 2022 22:57:01 +0300
Subject: [PATCH] fanotify: Fix stale file descriptor in copy_event_to_user()
Git-commit: ee12595147ac1fbfb5bcb23837e26dd58d94b15d
Patch-mainline: v5.17-rc3
References: bsc#1195187 CVE-2022-1998
 
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>
Acked-by: Jan Kara <jack@suse.cz>
---
 fs/notify/fanotify/fanotify_user.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
 
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -464,9 +464,6 @@ static ssize_t copy_event_to_user(struct
 	if (fanotify_is_perm_event(event->mask))
 		FANOTIFY_PERM(event)->fd = fd;
 
-	if (f)
-		fd_install(fd, f);
-
 	/* Event info records order is: dir fid + name, child fid */
 	if (fanotify_event_dir_fh_len(event)) {
 		info_type = info->name_len ? FAN_EVENT_INFO_TYPE_DFID_NAME :
@@ -530,6 +527,9 @@ static ssize_t copy_event_to_user(struct
 		count -= ret;
 	}
 
+	if (f)
+		fd_install(fd, f);
+
 	return metadata.event_len;
 
 out_close_fd: