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SubjectRe: [PATCH v3] virtio_vsock: Fix race condition in virtio_transport_recv_pkt
From
From: Jia He <justin.he@arm.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@arm.com>
> Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

Applied and queued up for -stable, thank you.

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