[PATCH net 2/3] vsock: Fix transport_g2h TOCTOU

[Michal Luczaj]

Function may race with vsock_core_unregister(): transport_g2h may become
NULL after the NULL check. Protect from a potential null-ptr-deref.

KASAN: null-ptr-deref in range [0x0000000000000118-0x000000000000011f]
RIP: 0010:vsock_find_cid+0x47/0x90
Call Trace:
 __vsock_bind+0x4b2/0x720
 vsock_bind+0x90/0xe0
 __sys_bind+0x14d/0x1e0
 __x64_sys_bind+0x6e/0xc0
 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 | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 
047d1bc773fab9c315a6ccd383a451fa11fb703e..337540efc237c8bc482a6730948fc773c00854f1
 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -533,8 +533,10 @@ EXPORT_SYMBOL_GPL(vsock_assign_transport);
 
 bool vsock_find_cid(unsigned int cid)
 {
-       if (transport_g2h && cid == transport_g2h->get_local_cid())
-               return true;
+       scoped_guard(mutex, &vsock_register_mutex) {
+               if (transport_g2h && cid == transport_g2h->get_local_cid())
+                       return true;
+       }
 
        if (transport_h2g && cid == VMADDR_CID_HOST)
                return true;

-- 
2.49.0