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From:   Alexander Popov <alex.popov@linux.com>
To:     David Miller <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Stefano Garzarella <sgarzare@redhat.com>,
        Jorgen Hansen <jhansen@vmware.com>,
        Stefan Schmidt <stefan@datenfreihafen.org>,
        Jeff Vander Stoep <jeffv@google.com>,
        Greg KH <greg@kroah.com>,
        Linus Torvalds <torvalds@linuxfoundation.org>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        alex.popov@linux.com
Subject: [PATCH 1/1] vsock: fix the race conditions in multi-transport support
Date:   Sun, 31 Jan 2021 13:59:14 +0300
Message-Id: <20210131105914.2217229-1-alex.popov@linux.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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.

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;
+
 		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