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SubjectRe: [PATCH net V2] vhost-vsock: fix use after free
On Thu, Sep 27, 2018 at 08:22:04PM +0800, Jason Wang wrote:
> The access of vsock is not protected by vhost_vsock_lock. This may
> lead to use after free since vhost_vsock_dev_release() may free the
> pointer at the same time.
>
> Fix this by holding the lock during the access.
>
> Reported-by: syzbot+e3e074963495f92a89ed@syzkaller.appspotmail.com
> Fixes: 16320f363ae1 ("vhost-vsock: add pkt cancel capability")
> Fixes: 433fc58e6bf2 ("VSOCK: Introduce vhost_vsock.ko")
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Wow is that really the best we can do? A global lock on a data path
operation? Granted use after free is nasty but Stefan said he sees
a way to fix it using a per socket refcount. He's on vacation
until Oct 4 though ...

> ---
> - V2: fix typos
> - The patch is needed for -stable.
> ---
> drivers/vhost/vsock.c | 26 +++++++++++++++++++-------
> 1 file changed, 19 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index 34bc3ab40c6d..7d0b292867fd 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -210,21 +210,27 @@ vhost_transport_send_pkt(struct virtio_vsock_pkt *pkt)
> struct vhost_vsock *vsock;
> int len = pkt->len;
>
> + spin_lock_bh(&vhost_vsock_lock);
> +
> /* Find the vhost_vsock according to guest context id */
> - vsock = vhost_vsock_get(le64_to_cpu(pkt->hdr.dst_cid));
> + vsock = __vhost_vsock_get(le64_to_cpu(pkt->hdr.dst_cid));
> if (!vsock) {
> virtio_transport_free_pkt(pkt);
> + spin_unlock_bh(&vhost_vsock_lock);
> return -ENODEV;
> }
>
> if (pkt->reply)
> atomic_inc(&vsock->queued_replies);
>
> - spin_lock_bh(&vsock->send_pkt_list_lock);
> + spin_lock(&vsock->send_pkt_list_lock);
> list_add_tail(&pkt->list, &vsock->send_pkt_list);
> - spin_unlock_bh(&vsock->send_pkt_list_lock);
> + spin_unlock(&vsock->send_pkt_list_lock);
>
> vhost_work_queue(&vsock->dev, &vsock->send_pkt_work);
> +
> + spin_unlock_bh(&vhost_vsock_lock);
> +
> return len;
> }
>
> @@ -236,18 +242,22 @@ vhost_transport_cancel_pkt(struct vsock_sock *vsk)
> int cnt = 0;
> LIST_HEAD(freeme);
>
> + spin_lock_bh(&vhost_vsock_lock);
> +
> /* Find the vhost_vsock according to guest context id */
> - vsock = vhost_vsock_get(vsk->remote_addr.svm_cid);
> - if (!vsock)
> + vsock = __vhost_vsock_get(vsk->remote_addr.svm_cid);
> + if (!vsock) {
> + spin_unlock_bh(&vhost_vsock_lock);
> return -ENODEV;
> + }
>
> - spin_lock_bh(&vsock->send_pkt_list_lock);
> + spin_lock(&vsock->send_pkt_list_lock);
> list_for_each_entry_safe(pkt, n, &vsock->send_pkt_list, list) {
> if (pkt->vsk != vsk)
> continue;
> list_move(&pkt->list, &freeme);
> }
> - spin_unlock_bh(&vsock->send_pkt_list_lock);
> + spin_unlock(&vsock->send_pkt_list_lock);
>
> list_for_each_entry_safe(pkt, n, &freeme, list) {
> if (pkt->reply)
> @@ -265,6 +275,8 @@ vhost_transport_cancel_pkt(struct vsock_sock *vsk)
> vhost_poll_queue(&tx_vq->poll);
> }
>
> + spin_unlock_bh(&vhost_vsock_lock);
> +
> return 0;
> }
>
> --
> 2.17.1

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