[PATCH] ipc/mqueue: release notification resources during inode eviction

[Daehyeon Ko <4ncienth@gmail.com>]

mqueue_flush_file() removes an mq_notify() registration only when the
closing task belongs to the thread group stored in notify_owner.

A task in a separate thread group created with CLONE_FILES can register
SIGEV_THREAD notification and exit without closing the shared file table.
If another thread group then unlinks and last-closes the queue, ->flush()
skips the registration and inode eviction loses the only pointers to its
resources.

The orphaned registration permanently retains the notification skb, its
netlink socket, a pid reference and a user namespace reference. An
unprivileged process can repeat the sequence with new queues and sockets.

No inode users remain during eviction. Remove any stale registration there
after dropping info->lock, since netlink_sendskb() may release the final
socket reference.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
---
A reproducer and regression selftest are available on request.

Tested on x86_64 KASAN at the stated base. The unpatched oracle reproduced
3/3 and the patched oracle passed 3/3, with no KASAN report, WARNING splat,
Oops or panic.

 ipc/mqueue.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index d1dd36a651b0..d1a1965c9811 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -528,6 +528,13 @@ static void mqueue_evict_inode(struct inode *inode)
 		list_add_tail(&msg->m_list, &tmp_msg);
 	kfree(info->node_cache);
 	spin_unlock(&info->lock);
+	/*
+	 * A shared file table can let the notification owner exit without
+	 * running ->flush(). No users of the inode remain during eviction, so
+	 * tear down any stale notification after dropping info->lock because
+	 * netlink_sendskb() may release the final socket reference.
+	 */
+	remove_notification(info);
 
 	list_for_each_entry_safe(msg, nmsg, &tmp_msg, m_list) {
 		list_del(&msg->m_list);

base-commit: 4352b8aee98005853aa63f57d6377282de17a33f
-- 
2.54.0