[PATCH net 1/3] vsock: Fix transport_{h2g,g2h} TOCTOU

[Michal Luczaj]

Checking transport_{h2g,g2h} != NULL may race with vsock_core_unregister().
Make sure pointers remain valid.

KASAN: null-ptr-deref in range [0x0000000000000118-0x000000000000011f]
RIP: 0010:vsock_dev_do_ioctl.isra.0+0x58/0xf0
Call Trace:
 __x64_sys_ioctl+0x12d/0x190
 do_syscall_64+0x92/0x1c0
 entry_SYSCALL_64_after_hwframe+0x4b/0x53

Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")
Signed-off-by: Michal Luczaj <m...@rbox.co>
---
 net/vmw_vsock/af_vsock.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 
2e7a3034e965db30b6ee295370d866e6d8b1c341..047d1bc773fab9c315a6ccd383a451fa11fb703e
 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -2541,6 +2541,8 @@ static long vsock_dev_do_ioctl(struct file *filp,
 
        switch (cmd) {
        case IOCTL_VM_SOCKETS_GET_LOCAL_CID:
+               mutex_lock(&vsock_register_mutex);
+
                /* To be compatible with the VMCI behavior, we prioritize the
                 * guest CID instead of well-know host CID (VMADDR_CID_HOST).
                 */
@@ -2549,6 +2551,8 @@ static long vsock_dev_do_ioctl(struct file *filp,
                else if (transport_h2g)
                        cid = transport_h2g->get_local_cid();
 
+               mutex_unlock(&vsock_register_mutex);
+
                if (put_user(cid, p) != 0)
                        retval = -EFAULT;
                break;

-- 
2.49.0