diff options
| author | Marc Zyngier <maz@kernel.org> | 2020-08-19 17:12:17 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-08-26 10:27:10 +0200 |
| commit | 89077f38db728c980dd0cc776400dff5c645f627 (patch) | |
| tree | a654ff9376a2ea209573a0c8d2339c43500eb506 | |
| parent | fabab559053d5e3f762e52d913cf689a9f242037 (diff) | |
epoll: Keep a reference on files added to the check list
commit a9ed4a6560b8562b7e2e2bed9527e88001f7b682 upstream.
When adding a new fd to an epoll, and that this new fd is an
epoll fd itself, we recursively scan the fds attached to it
to detect cycles, and add non-epool files to a "check list"
that gets subsequently parsed.
However, this check list isn't completely safe when deletions
can happen concurrently. To sidestep the issue, make sure that
a struct file placed on the check list sees its f_count increased,
ensuring that a concurrent deletion won't result in the file
disapearing from under our feet.
Cc: stable@vger.kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | fs/eventpoll.c | 9 |
1 files changed, 7 insertions, 2 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 240d9ceb8d0c..1a8224709d56 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -1719,9 +1719,11 @@ static int ep_loop_check_proc(void *priv, void *cookie, int call_nests) * not already there, and calling reverse_path_check() * during ep_insert(). */ - if (list_empty(&epi->ffd.file->f_tfile_llink)) + if (list_empty(&epi->ffd.file->f_tfile_llink)) { + get_file(epi->ffd.file); list_add(&epi->ffd.file->f_tfile_llink, &tfile_check_list); + } } } mutex_unlock(&ep->mtx); @@ -1765,6 +1767,7 @@ static void clear_tfile_check_list(void) file = list_first_entry(&tfile_check_list, struct file, f_tfile_llink); list_del_init(&file->f_tfile_llink); + fput(file); } INIT_LIST_HEAD(&tfile_check_list); } @@ -1906,9 +1909,11 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd, clear_tfile_check_list(); goto error_tgt_fput; } - } else + } else { + get_file(tf.file); list_add(&tf.file->f_tfile_llink, &tfile_check_list); + } mutex_lock_nested(&ep->mtx, 0); if (is_file_epoll(tf.file)) { tep = tf.file->private_data; |