[PATCH net] net/iucv: fix use-after-free of a severed iucv_path

[Bryam Vargas via B4 Relay]

From: Bryam Vargas <hexlabsecurity@xxxxxxxxx>

af_iucv queues not-yet-received message notifications on iucv->message_q,
each holding a raw pointer to the connection's iucv_path.  When the peer
severs the connection, iucv_sever_path() frees that path with
iucv_path_free() but leaves the notifications queued.  A later recvmsg()
drains message_q via iucv_process_message_q() and hands the stale path to
message_receive() -- a use-after-free of the freed iucv_path.

Drop the queued notifications when the path is severed; once the path is
gone they can no longer be received.  This also frees the notifications
leaked when a socket is closed with messages still queued.

Fixes: f0703c80e515 ("[AF_IUCV]: postpone receival of iucv-packets")
Closes: https://sashiko.dev/#/patchset/20260705-b4-disp-fc79c0dc-v1-1-d2cdcb57afa9@xxxxxxxxx?part=1
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Bryam Vargas <hexlabsecurity@xxxxxxxxx>
---
 net/iucv/af_iucv.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/net/iucv/af_iucv.c b/net/iucv/af_iucv.c
index fed240b453bd..2869a103f7fa 100644
--- a/net/iucv/af_iucv.c
+++ b/net/iucv/af_iucv.c
@@ -337,6 +337,7 @@ static void iucv_sever_path(struct sock *sk, int with_user_data)
 	unsigned char user_data[16];
 	struct iucv_sock *iucv = iucv_sk(sk);
 	struct iucv_path *path = iucv->path;
+	struct sock_msg_q *p, *n;
 
 	/* Whoever resets the path pointer, must sever and free it. */
 	if (xchg(&iucv->path, NULL)) {
@@ -348,6 +349,19 @@ static void iucv_sever_path(struct sock *sk, int with_user_data)
 		} else
 			pr_iucv->path_sever(path, NULL);
 		iucv_path_free(path);
+
+		/*
+		 * Message notifications queued on message_q still reference
+		 * the now freed path; drop them, otherwise a later recvmsg()
+		 * would pass the freed iucv_path to message_receive() via
+		 * iucv_process_message_q().
+		 */
+		spin_lock_bh(&iucv->message_q.lock);
+		list_for_each_entry_safe(p, n, &iucv->message_q.list, list) {
+			list_del(&p->list);
+			kfree(p);
+		}
+		spin_unlock_bh(&iucv->message_q.lock);
 	}
 }
 

---
base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
change-id: 20260707-b4-disp-783fedbb-39bc1bb9d4e0

Best regards,
-- 
Bryam Vargas <hexlabsecurity@xxxxxxxxx>