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

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@proton.me?part=1
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Link: https://patch.msgid.link/20260707-b4-disp-783fedbb-v1-1-463b9dbda2ea@proton.me
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/iucv/af_iucv.c b/net/iucv/af_iucv.c
index b85fb9767dec211918f7e8d6a16e88c0b20455b8..e3e71d168c47fdac57c3e42287bb6eab37293618 100644 (file)
--- 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);
        }
 }