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fanotify: Fix stale file descriptor in copy_event_to_user()

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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 <dan.carpenter@oracle.com>
Reviewed-by: Mathias Krause <minipli@grsecurity.net>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Dan Carpenter 2022-01-28 22:57:01 +03:00 committed by Greg Kroah-Hartman
parent 4d3fcfe846
commit 7b4741644c
1 changed files with 3 additions and 3 deletions
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6
fs/notify/fanotify/fanotify_user.c
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@ -366,9 +366,6 @@ 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);
/* 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 :
@ -432,6 +429,9 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
count -= ret;
}
if (f)
fd_install(fd, f);
return metadata.event_len;
out_close_fd: