From 60765e43e40fbf7a1df828116172440510fcc3e4 Mon Sep 17 00:00:00 2001 From: Dan Carpenter Date: Fri, 28 Jan 2022 22:57:01 +0300 Subject: [PATCH] fanotify: Fix stale file descriptor in copy_event_to_user() commit ee12595147ac1fbfb5bcb23837e26dd58d94b15d upstream. 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 Reviewed-by: Mathias Krause Signed-off-by: Jan Kara Signed-off-by: Greg Kroah-Hartman --- fs/notify/fanotify/fanotify_user.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c index 6facdf476255d1..84ec851211d91c 100644 --- a/fs/notify/fanotify/fanotify_user.c +++ b/fs/notify/fanotify/fanotify_user.c @@ -611,9 +611,6 @@ 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); @@ -621,6 +618,9 @@ 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: