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Commit 63059d09 authored by Marc Zyngier's avatar Marc Zyngier Committed by shaohanlin
Browse files

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: default avatarMarc Zyngier <maz@kernel.org>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>

(cherry picked from commit 9bbd2032)
parent 26991977

fs/eventpoll.c

+7 −2
Original line number Diff line number Diff line
@@ -1749,11 +1749,13 @@ 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);



	return error;
@@ -1795,6 +1797,7 @@ 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);

}
@@ -1949,9 +1952,11 @@ 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;