Commit 687aa0c5 authored by Michal Luczaj's avatar Michal Luczaj Committed by Jakub Kicinski
Browse files

vsock: Fix transport_* TOCTOU 



Transport assignment may race with module unload. Protect new_transport
from becoming a stale pointer.

This also takes care of an insecure call in vsock_use_local_transport();
add a lockdep assert.

BUG: unable to handle page fault for address: fffffbfff8056000
Oops: Oops: 0000 [#1] SMP KASAN
RIP: 0010:vsock_assign_transport+0x366/0x600
Call Trace:
 vsock_connect+0x59c/0xc40
 __sys_connect+0xe8/0x100
 __x64_sys_connect+0x6e/0xc0
 do_syscall_64+0x92/0x1c0
 entry_SYSCALL_64_after_hwframe+0x4b/0x53

Fixes: c0cfa2d8 ("vsock: add multi-transports support")
Reviewed-by: default avatarStefano Garzarella <sgarzare@redhat.com>
Signed-off-by: default avatarMichal Luczaj <mhal@rbox.co>
Link: https://patch.msgid.link/20250703-vsock-transports-toctou-v4-2-98f0eb530747@rbox.co


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 209fd720

net/vmw_vsock/af_vsock.c

+23 −5
Original line number Diff line number Diff line
@@ -407,6 +407,8 @@ EXPORT_SYMBOL_GPL(vsock_enqueue_accept); 


static bool vsock_use_local_transport(unsigned int remote_cid)

{

	lockdep_assert_held(&vsock_register_mutex);



	if (!transport_local)

		return false;
@@ -464,6 +466,8 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk) 


	remote_flags = vsk->remote_addr.svm_flags;



	mutex_lock(&vsock_register_mutex);



	switch (sk->sk_type) {

	case SOCK_DGRAM:

		new_transport = transport_dgram;
@@ -479,12 +483,15 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk) 
			new_transport = transport_h2g;

		break;

	default:

		return -ESOCKTNOSUPPORT;

		ret = -ESOCKTNOSUPPORT;

		goto err;

	}



	if (vsk->transport) {

		if (vsk->transport == new_transport)

			return 0;

		if (vsk->transport == new_transport) {

			ret = 0;

			goto err;

		}



		/* transport->release() must be called with sock lock acquired.

		 * This path can only be taken during vsock_connect(), where we
@@ -508,8 +515,16 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk) 
	/* We increase the module refcnt to prevent the transport unloading

	 * while there are open sockets assigned to it.

	 */

	if (!new_transport || !try_module_get(new_transport->module))

		return -ENODEV;

	if (!new_transport || !try_module_get(new_transport->module)) {

		ret = -ENODEV;

		goto err;

	}



	/* It's safe to release the mutex after a successful try_module_get().

	 * Whichever transport `new_transport` points at, it won't go away until

	 * the last module_put() below or in vsock_deassign_transport().

	 */

	mutex_unlock(&vsock_register_mutex);



	if (sk->sk_type == SOCK_SEQPACKET) {

		if (!new_transport->seqpacket_allow ||
@@ -528,6 +543,9 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk) 
	vsk->transport = new_transport;



	return 0;

err:

	mutex_unlock(&vsock_register_mutex);

	return ret;

}

EXPORT_SYMBOL_GPL(vsock_assign_transport);