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

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")

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

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

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

Thanks,
Stefano

On 01.02.2021 11:26, Stefano Garzarella wrote:

On Sun, Jan 31, 2021 at 01:59:14PM +0300, Alexander Popov wrote:

quoted

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")

quoted

Signed-off-by: Alexander Popov <redacted>
---
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.

quoted

+
		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>

Hello Stefano,

Thanks for the review.

I've just sent the v2.

Best regards,
Alexander