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

[Alexander Popov <alex.popov@linux.com>]

On 01.02.2021 11:26, Stefano Garzarella wrote:
> 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>

Hello Stefano,

Thanks for the review.

I've just sent the v2.

Best regards,
Alexander