Re: [PATCH net v2] vsock: fix potential null pointer dereference in vsock_poll()

[David Miller]

From: Stefano Garzarella <sgarzare@xxxxxxxxxx>
Date: Wed, 12 Aug 2020 14:56:02 +0200

> syzbot reported this issue where in the vsock_poll() we find the
> socket state at TCP_ESTABLISHED, but 'transport' is null:
>   general protection fault, probably for non-canonical address 0xdffffc0000000012: 0000 [#1] PREEMPT SMP KASAN
>   KASAN: null-ptr-deref in range [0x0000000000000090-0x0000000000000097]
>   CPU: 0 PID: 8227 Comm: syz-executor.2 Not tainted 5.8.0-rc7-syzkaller #0
>   Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>   RIP: 0010:vsock_poll+0x75a/0x8e0 net/vmw_vsock/af_vsock.c:1038
>   Call Trace:
>    sock_poll+0x159/0x460 net/socket.c:1266
>    vfs_poll include/linux/poll.h:90 [inline]
>    do_pollfd fs/select.c:869 [inline]
>    do_poll fs/select.c:917 [inline]
>    do_sys_poll+0x607/0xd40 fs/select.c:1011
>    __do_sys_poll fs/select.c:1069 [inline]
>    __se_sys_poll fs/select.c:1057 [inline]
>    __x64_sys_poll+0x18c/0x440 fs/select.c:1057
>    do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
>    entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> This issue can happen if the TCP_ESTABLISHED state is set after we read
> the vsk->transport in the vsock_poll().
> 
> We could put barriers to synchronize, but this can only happen during
> connection setup, so we can simply check that 'transport' is valid.
> 
> Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")
> Reported-and-tested-by: syzbot+a61bac2fcc1a7c6623fe@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>

Applied and queued up for -stable, thank you.