linux-kernel - Re: [PATCH v3] virtio_vsock: Fix race condition in virtio_transport_recv

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Date:   Sat, 30 May 2020 17:44:45 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     justin.he@....com
Cc:     stefanha@...hat.com, sgarzare@...hat.com, kuba@...nel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kaly.Xin@....com, stable@...r.kernel.org
Subject: Re: [PATCH v3] virtio_vsock: Fix race condition in
 virtio_transport_recv_pkt

From: Jia He <justin.he@....com>
Date: Sat, 30 May 2020 09:38:28 +0800

> When client on the host tries to connect(SOCK_STREAM, O_NONBLOCK) to the
> server on the guest, there will be a panic on a ThunderX2 (armv8a server):
 ...
> The race condition is as follows:
> Task1                                Task2
> =====                                =====
> __sock_release                       virtio_transport_recv_pkt
>   __vsock_release                      vsock_find_bound_socket (found sk)
>     lock_sock_nested
>     vsock_remove_sock
>     sock_orphan
>       sk_set_socket(sk, NULL)
>     sk->sk_shutdown = SHUTDOWN_MASK
>     ...
>     release_sock
>                                     lock_sock
>                                        virtio_transport_recv_connecting
>                                          sk->sk_socket->state (panic!)
> 
> The root cause is that vsock_find_bound_socket can't hold the lock_sock,
> so there is a small race window between vsock_find_bound_socket() and
> lock_sock(). If __vsock_release() is running in another task,
> sk->sk_socket will be set to NULL inadvertently.
> 
> This fixes it by checking sk->sk_shutdown(suggested by Stefano) after
> lock_sock since sk->sk_shutdown is set to SHUTDOWN_MASK under the
> protection of lock_sock_nested.
> 
> Signed-off-by: Jia He <justin.he@....com>
> Reviewed-by: Stefano Garzarella <sgarzare@...hat.com>

Applied and queued up for -stable, thank you.