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