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Message-ID: <77plpkw3mp4r3ue4ubmh4yhqfo777koiu65dqfqfxmjgc5uq57@aifi6mhtgtuj>
Date: Thu, 9 Jan 2025 10:01:31 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: Hyunwoo Kim <v4bel@...ori.io>
Cc: netdev@...r.kernel.org, Simon Horman <horms@...nel.org>,
Stefan Hajnoczi <stefanha@...hat.com>, linux-kernel@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Wongi Lee <qwerty@...ori.io>,
"David S. Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>,
Jason Wang <jasowang@...hat.com>, Bobby Eshleman <bobby.eshleman@...edance.com>,
virtualization@...ts.linux.dev, Eugenio Pérez <eperezma@...hat.com>,
Luigi Leonardi <leonardi@...hat.com>, bpf@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
"Michael S. Tsirkin" <mst@...hat.com>, Michal Luczaj <mhal@...x.co>, kvm@...r.kernel.org,
imv4bel@...il.com
Subject: Re: [PATCH net 1/2] vsock/virtio: discard packets if the transport
changes
On Wed, Jan 08, 2025 at 02:31:19PM -0500, Hyunwoo Kim wrote:
>On Wed, Jan 08, 2025 at 07:06:16PM +0100, Stefano Garzarella wrote:
>> 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 <v4bel@...ori.io>
>> Reported-by: Wongi Lee <qwerty@...ori.io>
>> Closes: https://lore.kernel.org/netdev/Z2LvdTTQR7dBmPb5@v4bel-B760M-AORUS-ELITE-AX/
>> Signed-off-by: Stefano Garzarella <sgarzare@...hat.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)) {
>
>If a race scenario with vsock_listen() is added to the existing
>race scenario, the patch can be bypassed.
>
>In addition to the existing scenario:
>```
> cpu0 cpu1
>
> socket(A)
>
> bind(A, {cid: VMADDR_CID_LOCAL, port: 1024})
> vsock_bind()
>
> listen(A)
> vsock_listen()
> socket(B)
>
> connect(B, {cid: VMADDR_CID_LOCAL, port: 1024})
> vsock_connect()
> lock_sock(sk);
> virtio_transport_connect()
> virtio_transport_connect()
> virtio_transport_send_pkt_info()
> vsock_loopback_send_pkt(VIRTIO_VSOCK_OP_REQUEST)
> queue_work(vsock_loopback_work)
> sk->sk_state = TCP_SYN_SENT;
> release_sock(sk);
> vsock_loopback_work()
> virtio_transport_recv_pkt(VIRTIO_VSOCK_OP_REQUEST)
> sk = vsock_find_bound_socket(&dst);
> virtio_transport_recv_listen(sk, skb)
> child = vsock_create_connected(sk);
> vsock_assign_transport()
> vvs = kzalloc(sizeof(*vvs), GFP_KERNEL);
> vsock_insert_connected(vchild);
> list_add(&vsk->connected_table, list);
> virtio_transport_send_response(vchild, skb);
> virtio_transport_send_pkt_info()
> vsock_loopback_send_pkt(VIRTIO_VSOCK_OP_RESPONSE)
> queue_work(vsock_loopback_work)
>
> vsock_loopback_work()
> virtio_transport_recv_pkt(VIRTIO_VSOCK_OP_RESPONSE)
> sk = vsock_find_bound_socket(&dst);
> lock_sock(sk);
> case TCP_SYN_SENT:
> virtio_transport_recv_connecting()
> sk->sk_state = TCP_ESTABLISHED;
> release_sock(sk);
>
> kill(connect(B));
> lock_sock(sk);
> if (signal_pending(current)) {
> sk->sk_state = sk->sk_state == TCP_ESTABLISHED ? TCP_CLOSING : TCP_CLOSE;
> sock->state = SS_UNCONNECTED; // [1]
> release_sock(sk);
>
> connect(B, {cid: VMADDR_CID_HYPERVISOR, port: 1024})
> vsock_connect(B)
> lock_sock(sk);
> vsock_assign_transport()
> virtio_transport_release()
> virtio_transport_close()
> if (!(sk->sk_state == TCP_ESTABLISHED || sk->sk_state == TCP_CLOSING))
> virtio_transport_shutdown()
> virtio_transport_send_pkt_info()
> vsock_loopback_send_pkt(VIRTIO_VSOCK_OP_SHUTDOWN)
> queue_work(vsock_loopback_work)
> schedule_delayed_work(&vsk->close_work, VSOCK_CLOSE_TIMEOUT); // [5]
> vsock_deassign_transport()
> vsk->transport = NULL;
> return -ESOCKTNOSUPPORT;
> release_sock(sk);
> vsock_loopback_work()
> virtio_transport_recv_pkt(VIRTIO_VSOCK_OP_SHUTDOWN)
> virtio_transport_recv_connected()
> virtio_transport_reset()
> virtio_transport_send_pkt_info()
> vsock_loopback_send_pkt(VIRTIO_VSOCK_OP_RST)
> queue_work(vsock_loopback_work)
> listen(B)
> vsock_listen()
> if (sock->state != SS_UNCONNECTED) // [2]
> sk->sk_state = TCP_LISTEN; // [3]
>
> vsock_loopback_work()
> virtio_transport_recv_pkt(VIRTIO_VSOCK_OP_RST)
> if ((sk->sk_state != TCP_LISTEN && vsk->transport != &t->transport)) { // [4]
> ...
>
> virtio_transport_close_timeout()
> virtio_transport_do_close()
> vsock_stream_has_data()
> return vsk->transport->stream_has_data(vsk); // null-ptr-deref
>
>```
>(Yes, This is quite a crazy scenario, but it can actually be induced)
>
>Since sock->state is set to SS_UNCONNECTED during the first connect()[1],
>it can pass the sock->state check[2] in vsock_listen() and set
>sk->sk_state to TCP_LISTEN[3].
>If this happens, the check in the patch with
>`sk->sk_state != TCP_LISTEN` will pass[4], and a null-ptr-deref can
>still occur.)
>
>More specifically, because the sk_state has changed to TCP_LISTEN,
>virtio_transport_recv_disconnecting() will not be called by the
>loopback worker. However, a null-ptr-deref may occur in
>virtio_transport_close_timeout(), which is scheduled by
>virtio_transport_close() called in the flow of the second connect()[5].
>(The patch no longer cancels the virtio_transport_close_timeout() worker)
>
>And even if the `sk->sk_state != TCP_LISTEN` check is removed from the
>patch, it seems that a null-ptr-deref will still occur due to
>virtio_transport_close_timeout().
>It might be necessary to add worker cancellation at the
>appropriate location.
Thanks for the analysis!
Do you have time to cook a proper patch to cover this scenario?
Or we should mix this fix together with your patch (return 0 in
vsock_stream_has_data()) while we investigate a better handling?
Thanks,
Stefano
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