vsock: Fix transport_{g2h,h2g} TOCTOU

In the Linux kernel, the following vulnerability has been resolved:

vsock: Fix transport_{g2h,h2g} TOCTOU

vsock_find_cid() and vsock_dev_do_ioctl() may race with module unload.

transport_{g2h,h2g} may become NULL after the NULL check.

Introduce vsock_transport_local_cid() to 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

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