Re: [PATCH 1/1] vsock: fix the race conditions in multi-transport support

[Stefano Garzarella <sgarzare@redhat.com>]

On Sun, Jan 31, 2021 at 01:59:14PM +0300, Alexander Popov wrote:
>There are multiple similar bugs implicitly introduced by the
>commit c0cfa2d8a788fcf4 ("vsock: add multi-transports support") and
>commit 6a2c0962105ae8ce ("vsock: prevent transport modules unloading").
>
>The bug pattern:
> [1] vsock_sock.transport pointer is copied to a local variable,
> [2] lock_sock() is called,
> [3] the local variable is used.
>VSOCK multi-transport support introduced the race condition:
>vsock_sock.transport value may change between [1] and [2].
>
>Let's copy vsock_sock.transport pointer to local variables after
>the lock_sock() call.

We can add:

Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")

>
>Signed-off-by: Alexander Popov <alex.popov@linux.com>
>---
> net/vmw_vsock/af_vsock.c | 17 ++++++++++++-----
> 1 file changed, 12 insertions(+), 5 deletions(-)
>
>diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>index d10916ab4526..28edac1f9aa6 100644
>--- a/net/vmw_vsock/af_vsock.c
>+++ b/net/vmw_vsock/af_vsock.c
>@@ -997,9 +997,12 @@ static __poll_t vsock_poll(struct file *file, struct socket *sock,
> 			mask |= EPOLLOUT | EPOLLWRNORM | EPOLLWRBAND;
>
> 	} else if (sock->type == SOCK_STREAM) {
>-		const struct vsock_transport *transport = vsk->transport;
>+		const struct vsock_transport *transport = NULL;

I think we can avoid initializing to NULL since we assign it shortly 
after.

>+
> 		lock_sock(sk);
>
>+		transport = vsk->transport;
>+
> 		/* Listening sockets that have connections in their accept
> 		 * queue can be read.
> 		 */
>@@ -1082,10 +1085,11 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> 	err = 0;
> 	sk = sock->sk;
> 	vsk = vsock_sk(sk);
>-	transport = vsk->transport;
>
> 	lock_sock(sk);
>
>+	transport = vsk->transport;
>+
> 	err = vsock_auto_bind(vsk);
> 	if (err)
> 		goto out;
>@@ -1544,10 +1548,11 @@ static int vsock_stream_setsockopt(struct 
>socket *sock,
> 	err = 0;
> 	sk = sock->sk;
> 	vsk = vsock_sk(sk);
>-	transport = vsk->transport;
>
> 	lock_sock(sk);
>
>+	transport = vsk->transport;
>+
> 	switch (optname) {
> 	case SO_VM_SOCKETS_BUFFER_SIZE:
> 		COPY_IN(val);
>@@ -1680,7 +1685,6 @@ static int vsock_stream_sendmsg(struct socket *sock, struct msghdr *msg,
>
> 	sk = sock->sk;
> 	vsk = vsock_sk(sk);
>-	transport = vsk->transport;
> 	total_written = 0;
> 	err = 0;
>
>@@ -1689,6 +1693,8 @@ static int vsock_stream_sendmsg(struct socket *sock, struct msghdr *msg,
>
> 	lock_sock(sk);
>
>+	transport = vsk->transport;
>+
> 	/* Callers should not provide a destination with stream sockets. */
> 	if (msg->msg_namelen) {
> 		err = sk->sk_state == TCP_ESTABLISHED ? -EISCONN : -EOPNOTSUPP;
>@@ -1823,11 +1829,12 @@ vsock_stream_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>
> 	sk = sock->sk;
> 	vsk = vsock_sk(sk);
>-	transport = vsk->transport;
> 	err = 0;
>
> 	lock_sock(sk);
>
>+	transport = vsk->transport;
>+
> 	if (!transport || sk->sk_state != TCP_ESTABLISHED) {
> 		/* Recvmsg is supposed to return 0 if a peer performs an
> 		 * orderly shutdown. Differentiate between that case and when a
>-- 
>2.26.2
>

Thanks for fixing this issues. With the small changes applied:

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

Thanks,
Stefano