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fanotify: Fix stale file descriptor in copy_event_to_user()

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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: f644bc449b ("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>
This commit is contained in:
Dan Carpenter 2022-01-28 22:57:01 +03:00 • committed by Jan Kara
parent 26291c54e1
commit ee12595147
1 changed files with 3 additions and 3 deletions
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6
fs/notify/fanotify/fanotify_user.c
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@ -701,9 +701,6 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
if (fanotify_is_perm_event(event->mask)) if (fanotify_is_perm_event(event->mask))
FANOTIFY_PERM(event)->fd = fd; FANOTIFY_PERM(event)->fd = fd;
if (f)
fd_install(fd, f);
if (info_mode) { if (info_mode) {
ret = copy_info_records_to_user(event, info, info_mode, pidfd, ret = copy_info_records_to_user(event, info, info_mode, pidfd,
buf, count); buf, count);
@ -711,6 +708,9 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
goto out_close_fd; goto out_close_fd;
} }
if (f)
fd_install(fd, f);
return metadata.event_len; return metadata.event_len;
out_close_fd: out_close_fd: