[PATCH net v3 2/2] vsock/vmci: validate packet source for connected sockets

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

vmci_transport_recv_stream_cb() looks up sockets first by the full source
and destination tuple, then by destination only in the bound table. The
fallback can select a non-listening socket without checking whether the
packet came from its stored peer.

This was reproduced with two VMCI contexts. A RST from the context not
stored in a TCP_SYN_SENT socket reset that socket after it was selected by
the destination-only lookup.

VMCI can process notification packets in bottom-half context when the
socket is not owned by user context, or defer packets to a workqueue. Use
vsock_check_source() after taking the socket lock in the bottom-half path,
and recheck after lock_sock() in the workqueue path. Listening sockets
continue to accept packets from any source.

Fixes: d021c344051a ("VSOCK: Introduce VM Sockets")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/netdev/20260814121255.6B5001F000E9@smtp.kernel.org/
Cc: stable@vger.kernel.org
Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
---
 net/vmw_vsock/vmci_transport.c | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/net/vmw_vsock/vmci_transport.c b/net/vmw_vsock/vmci_transport.c
index 1c4ee039c..b612a9893 100644
--- a/net/vmw_vsock/vmci_transport.c
+++ b/net/vmw_vsock/vmci_transport.c
@@ -680,11 +680,13 @@ static int vmci_transport_recv_stream_cb(void *data, struct vmci_datagram *dg)
 	struct vmci_transport_packet *pkt;
 	struct vsock_sock *vsk;
 	bool bh_process_pkt;
+	bool drop_pkt;
 	int err;
 
 	sk = NULL;
 	err = VMCI_SUCCESS;
 	bh_process_pkt = false;
+	drop_pkt = false;
 
 	/* Ignore incoming packets from resources that aren't vsock
 	 * implementations.
@@ -765,17 +767,26 @@ static int vmci_transport_recv_stream_cb(void *data, struct vmci_datagram *dg)
 	bh_lock_sock(sk);
 
 	if (!sock_owned_by_user(sk)) {
-		/* The local context ID may be out of date, update it. */
-		vsk->local_addr.svm_cid = dst.svm_cid;
+		if (sk->sk_state != TCP_LISTEN &&
+		    !vsock_check_source(vsk, &vmci_transport, &src)) {
+			drop_pkt = true;
+			err = VMCI_ERROR_NO_ACCESS;
+		} else {
+			/* The local context ID may be out of date, update it. */
+			vsk->local_addr.svm_cid = dst.svm_cid;
 
-		if (sk->sk_state == TCP_ESTABLISHED)
-			vmci_trans(vsk)->notify_ops->handle_notify_pkt(
-					sk, pkt, true, &dst, &src,
-					&bh_process_pkt);
+			if (sk->sk_state == TCP_ESTABLISHED)
+				vmci_trans(vsk)->notify_ops->handle_notify_pkt(sk, pkt, true,
+									       &dst, &src,
+									       &bh_process_pkt);
+		}
 	}
 
 	bh_unlock_sock(sk);
 
+	if (drop_pkt)
+		goto out;
+
 	if (!bh_process_pkt) {
 		struct vmci_transport_recv_pkt_info *recv_pkt_info;
 
@@ -900,6 +911,7 @@ static void vmci_transport_recv_pkt_work(struct work_struct *work)
 {
 	struct vmci_transport_recv_pkt_info *recv_pkt_info;
 	struct vmci_transport_packet *pkt;
+	struct sockaddr_vm src;
 	struct sock *sk;
 
 	recv_pkt_info =
@@ -908,6 +920,10 @@ static void vmci_transport_recv_pkt_work(struct work_struct *work)
 	pkt = &recv_pkt_info->pkt;
 
 	lock_sock(sk);
+	vsock_addr_init(&src, pkt->dg.src.context, pkt->src_port);
+	if (sk->sk_state != TCP_LISTEN &&
+	    !vsock_check_source(vsock_sk(sk), &vmci_transport, &src))
+		goto out;
 
 	/* The local context ID may be out of date. */
 	vsock_sk(sk)->local_addr.svm_cid = pkt->dg.dst.context;
@@ -937,6 +953,7 @@ static void vmci_transport_recv_pkt_work(struct work_struct *work)
 		break;
 	}
 
+out:
 	release_sock(sk);
 	kfree(recv_pkt_info);
 	/* Release reference obtained in the stream callback when we fetched
-- 
2.54.0