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| author | Marc Zyngier <maz@kernel.org> | 2020-08-19 17:12:17 +0100 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2020-08-22 18:23:57 -0400 |
| commit | a9ed4a6560b8562b7e2e2bed9527e88001f7b682 (patch) | |
| tree | 0769da3ad923b7c84ce4eb86fd2bc3e9fde6efe6 | |
| parent | 9123e3a74ec7b934a4a099e98af6a61c2f80bbf5 (diff) | |
| download | linux-a9ed4a6560b8562b7e2e2bed9527e88001f7b682.tar.gz linux-a9ed4a6560b8562b7e2e2bed9527e88001f7b682.tar.bz2 linux-a9ed4a6560b8562b7e2e2bed9527e88001f7b682.zip | |
epoll: Keep a reference on files added to the check list
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>
| -rw-r--r-- | fs/eventpoll.c | 11 |
1 files changed, 9 insertions, 2 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 12eebcdea9c8..196003d9242c 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -1994,9 +1994,11 @@ 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); @@ -2040,6 +2042,7 @@ 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); } @@ -2204,13 +2207,17 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds, clear_tfile_check_list(); goto error_tgt_fput; } - } else + } else { + get_file(tf.file); list_add(&tf.file->f_tfile_llink, &tfile_check_list); + } error = epoll_mutex_lock(&ep->mtx, 0, nonblock); if (error) { out_del: list_del(&tf.file->f_tfile_llink); + if (!is_file_epoll(tf.file)) + fput(tf.file); goto error_tgt_fput; } if (is_file_epoll(tf.file)) { |