[PATCH] net/vmw_vsock: fix NULL pointer deref and improve locking

[Norbert Slusarek]

From: Norbert Slusarek <nslusa...@gmx.net>
Date: Thu, 4 Feb 2021 18:49:24 +0100
Subject: [PATCH] net/vmw_vsock: fix NULL pointer deref and improve locking

In vsock_stream_connect(), a thread will enter schedule_timeout().
While being scheduled out, another thread can enter vsock_stream_connect() as
well and set vsk->transport to NULL. In case a signal was sent, the first
thread can leave schedule_timeout() and vsock_transport_cancel_pkt() will be
called right after. Inside vsock_transport_cancel_pkt(), a null dereference
will happen on transport->cancel_pkt.

The patch also features improved locking inside vsock_connect_timeout().

Signed-off-by: Norbert Slusarek <nslusa...@gmx.net>
---
 net/vmw_vsock/af_vsock.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 3b480ed0953a..ea7b9d208724 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -1233,7 +1233,7 @@ static int vsock_transport_cancel_pkt(struct vsock_sock 
*vsk)
 {
        const struct vsock_transport *transport = vsk->transport;

-       if (!transport->cancel_pkt)
+       if (!transport || !transport->cancel_pkt)
                return -EOPNOTSUPP;

        return transport->cancel_pkt(vsk);
@@ -1243,7 +1243,6 @@ static void vsock_connect_timeout(struct work_struct 
*work)
 {
        struct sock *sk;
        struct vsock_sock *vsk;
-       int cancel = 0;

        vsk = container_of(work, struct vsock_sock, connect_work.work);
        sk = sk_vsock(vsk);
@@ -1254,11 +1253,9 @@ static void vsock_connect_timeout(struct work_struct 
*work)
                sk->sk_state = TCP_CLOSE;
                sk->sk_err = ETIMEDOUT;
                sk->sk_error_report(sk);
-               cancel = 1;
+               vsock_transport_cancel_pkt(vsk);
        }
        release_sock(sk);
-       if (cancel)
-               vsock_transport_cancel_pkt(vsk);

        sock_put(sk);
 }
--
2.30.0