On Thu, Jan 09, 2025 at 02:34:28PM +0100, Michal Luczaj wrote:

On 1/8/25 19:06, Stefano Garzarella wrote:

quoted

If the socket has been de-assigned or assigned to another transport,
we must discard any packets received because they are not expected
and would cause issues when we access vsk->transport.

A possible scenario is described by Hyunwoo Kim in the attached link,
where after a first connect() interrupted by a signal, and a second
connect() failed, we can find `vsk->transport` at NULL, leading to a
NULL pointer dereference.

Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")
Reported-by: Hyunwoo Kim <redacted>
Reported-by: Wongi Lee <redacted>
Closes: https://lore.kernel.org/netdev/Z2LvdTTQR7dBmPb5@v4bel-B760M-AORUS-ELITE-AX/ (local)
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 net/vmw_vsock/virtio_transport_common.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 9acc13ab3f82..51a494b69be8 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c

@@ -1628,8 +1628,11 @@ void virtio_transport_recv_pkt(struct virtio_transport *t,

 	lock_sock(sk);

-	/* Check if sk has been closed before lock_sock */
-	if (sock_flag(sk, SOCK_DONE)) {
+	/* Check if sk has been closed or assigned to another transport before
+	 * lock_sock (note: listener sockets are not assigned to any transport)
+	 */
+	if (sock_flag(sk, SOCK_DONE) ||
+	    (sk->sk_state != TCP_LISTEN && vsk->transport != &t->transport)) {
 		(void)virtio_transport_reset_no_sock(t, skb);
 		release_sock(sk);
 		sock_put(sk);

FWIW, I've tried simplifying Hyunwoo's repro to toy with some tests. Ended
up with

from threading import *
from socket import *
from signal import *

def listener(tid):
while True:
	s = socket(AF_VSOCK, SOCK_SEQPACKET)
	s.bind((1, 1234))
	s.listen()
	pthread_kill(tid, SIGUSR1)

signal(SIGUSR1, lambda *args: None)
Thread(target=listener, args=[get_ident()]).start()

while True:
c = socket(AF_VSOCK, SOCK_SEQPACKET)
c.connect_ex((1, 1234))
c.connect_ex((42, 1234))

which gives me splats with or without this patch.

Thanks again for the repro, it worked for me, only if a G2H transport
wasn't loaeded (e.g. virtio-vsock driver).

I tested on the v2 I just sent [1], and I can't see the kernel oops
anymore, but please do test/review too.

Thanks,
Stefano

[1] https://lore.kernel.org/netdev/20250110083511.30419-1-sgarzare@redhat.com/ (local)