Hi Stefano
> -----Original Message-----
> From: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> Sent: Saturday, May 30, 2020 12:34 AM
> To: Justin He <Justin.He@xxxxxxx>
> Cc: Stefan Hajnoczi <stefanha@xxxxxxxxxx>; David S. Miller
> <davem@xxxxxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>;
> kvm@xxxxxxxxxxxxxxx; virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx;
> netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Kaly Xin
> <Kaly.Xin@xxxxxxx>; stable@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v2] virtio_vsock: Fix race condition in
> virtio_transport_recv_pkt
>
> On Fri, May 29, 2020 at 11:21:02PM +0800, Jia He wrote:
> > When client tries to connect(SOCK_STREAM) the server in the guest with
> > NONBLOCK mode, there will be a panic on a ThunderX2 (armv8a server):
> > [ 463.718844][ T5040] Unable to handle kernel NULL pointer dereference
> at virtual address 0000000000000000
> > [ 463.718848][ T5040] Mem abort info:
> > [ 463.718849][ T5040] ESR = 0x96000044
> > [ 463.718852][ T5040] EC = 0x25: DABT (current EL), IL = 32 bits
> > [ 463.718853][ T5040] SET = 0, FnV = 0
> > [ 463.718854][ T5040] EA = 0, S1PTW = 0
> > [ 463.718855][ T5040] Data abort info:
> > [ 463.718856][ T5040] ISV = 0, ISS = 0x00000044
> > [ 463.718857][ T5040] CM = 0, WnR = 1
> > [ 463.718859][ T5040] user pgtable: 4k pages, 48-bit VAs,
> pgdp=0000008f6f6e9000
> > [ 463.718861][ T5040] [0000000000000000] pgd=0000000000000000
> > [ 463.718866][ T5040] Internal error: Oops: 96000044 [#1] SMP
> > [...]
> > [ 463.718977][ T5040] CPU: 213 PID: 5040 Comm: vhost-5032 Tainted: G
> O 5.7.0-rc7+ #139
> > [ 463.718980][ T5040] Hardware name: GIGABYTE R281-T91-00/MT91-FS1-00,
> BIOS F06 09/25/2018
> > [ 463.718982][ T5040] pstate: 60400009 (nZCv daif +PAN -UAO)
> > [ 463.718995][ T5040] pc : virtio_transport_recv_pkt+0x4c8/0xd40
> [vmw_vsock_virtio_transport_common]
> > [ 463.718999][ T5040] lr : virtio_transport_recv_pkt+0x1fc/0xd40
> [vmw_vsock_virtio_transport_common]
> > [ 463.719000][ T5040] sp : ffff80002dbe3c40
> > [...]
> > [ 463.719025][ T5040] Call trace:
> > [ 463.719030][ T5040] virtio_transport_recv_pkt+0x4c8/0xd40
> [vmw_vsock_virtio_transport_common]
> > [ 463.719034][ T5040] vhost_vsock_handle_tx_kick+0x360/0x408
> [vhost_vsock]
> > [ 463.719041][ T5040] vhost_worker+0x100/0x1a0 [vhost]
> > [ 463.719048][ T5040] kthread+0x128/0x130
> > [ 463.719052][ T5040] ret_from_fork+0x10/0x18
> ^ ^
> Maybe we can remove these two columns from the commit message.
>
> >
> > The race condition as follows:
> > Task1 Task2
> > ===== =====
> > __sock_release virtio_transport_recv_pkt
> > __vsock_release vsock_find_bound_socket (found)
> > lock_sock_nested
> > vsock_remove_sock
> > sock_orphan
> > sk_set_socket(sk, NULL)
>
> Here we can add:
> sk->sk_shutdown = SHUTDOWN_MASK;
Indeed. This makes it more clearly
--
Cheers,
Justin (Jia He)
>
> > ...
> > 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 there is __vsock_release() in another task, sk->sk_socket
> > will be set to NULL inadvertently.
> >
> > This fixes it by checking sk->sk_shutdown.
> >
> > Signed-off-by: Jia He <justin.he@xxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > Cc: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> > ---
> > v2: use lightweight checking suggested by Stefano Garzarella
> >
> > net/vmw_vsock/virtio_transport_common.c | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/net/vmw_vsock/virtio_transport_common.c
> b/net/vmw_vsock/virtio_transport_common.c
> > index 69efc891885f..0edda1edf988 100644
> > --- a/net/vmw_vsock/virtio_transport_common.c
> > +++ b/net/vmw_vsock/virtio_transport_common.c
> > @@ -1132,6 +1132,14 @@ void virtio_transport_recv_pkt(struct
> virtio_transport *t,
> >
> > lock_sock(sk);
> >
> > +/* Check if sk has been released before lock_sock */
> > +if (sk->sk_shutdown == SHUTDOWN_MASK) {
> > +(void)virtio_transport_reset_no_sock(t, pkt);
> > +release_sock(sk);
> > +sock_put(sk);
> > +goto free_pkt;
> > +}
> > +
> > /* Update CID in case it has changed after a transport reset event */
> > vsk->local_addr.svm_cid = dst.svm_cid;
> >
> > --
> > 2.17.1
> >
>
> Anyway, the patch LGTM, let see what David and other say.
>
> Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
>
> Thanks,
> Stefano
IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.
