vsock: fix locking in vsock_shutdown()

In vsock_shutdown() we touched some socket fields without holding the
socket lock, such as 'state' and 'sk_flags'.

Also, after the introduction of multi-transport, we are accessing
'vsk->transport' in vsock_send_shutdown() without holding the lock
and this call can be made while the connection is in progress, so
the transport can change in the meantime.

To avoid issues, we hold the socket lock when we enter in
vsock_shutdown() and release it when we leave.

Among the transports that implement the 'shutdown' callback, only
hyperv_transport acquired the lock. Since the caller now holds it,
we no longer take it.

Fixes: d021c344051a ("VSOCK: Introduce VM Sockets")
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
v2:
- removed 'sk' variable is hvs_shutdown_lock_held, since it is unused
  after these changes
---
 net/vmw_vsock/af_vsock.c         | 8 +++++---
 net/vmw_vsock/hyperv_transport.c | 4 ----
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 4ea301fc2bf0..5546710d8ac1 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c

@@ -943,10 +943,12 @@ static int vsock_shutdown(struct socket *sock, int mode)
 	 */
 
 	sk = sock->sk;
+
+	lock_sock(sk);
 	if (sock->state == SS_UNCONNECTED) {
 		err = -ENOTCONN;
 		if (sk->sk_type == SOCK_STREAM)
-			return err;
+			goto out;
 	} else {
 		sock->state = SS_DISCONNECTING;
 		err = 0;

@@ -955,10 +957,8 @@ static int vsock_shutdown(struct socket *sock, int mode)
 	/* Receive and send shutdowns are treated alike. */
 	mode = mode & (RCV_SHUTDOWN | SEND_SHUTDOWN);
 	if (mode) {
-		lock_sock(sk);
 		sk->sk_shutdown |= mode;
 		sk->sk_state_change(sk);
-		release_sock(sk);
 
 		if (sk->sk_type == SOCK_STREAM) {
 			sock_reset_flag(sk, SOCK_DONE);

@@ -966,6 +966,8 @@ static int vsock_shutdown(struct socket *sock, int mode)
 		}
 	}
 
+out:
+	release_sock(sk);
 	return err;
 }
 

diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
index 630b851f8150..cc3bae2659e7 100644
--- a/net/vmw_vsock/hyperv_transport.c
+++ b/net/vmw_vsock/hyperv_transport.c

@@ -474,14 +474,10 @@ static void hvs_shutdown_lock_held(struct hvsock *hvs, int mode)
 
 static int hvs_shutdown(struct vsock_sock *vsk, int mode)
 {
-	struct sock *sk = sk_vsock(vsk);
-
 	if (!(mode & SEND_SHUTDOWN))
 		return 0;
 
-	lock_sock(sk);
 	hvs_shutdown_lock_held(vsk->trans, mode);
-	release_sock(sk);
 	return 0;
 }
 

-- 
2.29.2

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Tue,  9 Feb 2021 09:52:19 +0100 you wrote:

In vsock_shutdown() we touched some socket fields without holding the
socket lock, such as 'state' and 'sk_flags'.

Also, after the introduction of multi-transport, we are accessing
'vsk->transport' in vsock_send_shutdown() without holding the lock
and this call can be made while the connection is in progress, so
the transport can change in the meantime.

[...]

Here is the summary with links:
  - [net,v2] vsock: fix locking in vsock_shutdown()
    https://git.kernel.org/netdev/net/c/1c5fae9c9a09

You are awesome, thank you!
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