linux-kernel - Re: [syzbot] [kvm?] [net?] [virt?] general protection fault in virtio_transport_purge

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Date:   Fri, 24 Mar 2023 10:06:21 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     syzbot <syzbot+befff0a9536049e7902e@...kaller.appspotmail.com>,
        Bobby Eshleman <bobby.eshleman@...edance.com>,
        Bobby Eshleman <bobby.eshleman@...il.com>
Cc:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, pabeni@...hat.com, stefanha@...hat.com,
        syzkaller-bugs@...glegroups.com,
        virtualization@...ts.linux-foundation.org,
        Krasnov Arseniy <oxffffaa@...il.com>,
        Krasnov Arseniy Vladimirovich <AVKrasnov@...rdevices.ru>
Subject: Re: [syzbot] [kvm?] [net?] [virt?] general protection fault in
 virtio_transport_purge_skbs

On Fri, Mar 24, 2023 at 9:55 AM Stefano Garzarella <sgarzare@...hat.com> wrote:
>
> On Fri, Mar 24, 2023 at 9:31 AM Stefano Garzarella <sgarzare@...hat.com> wrote:
> >
> > Hi Bobby,
> > can you take a look at this report?
> >
> > It seems related to the changes we made to support skbuff.
>
> Could it be a problem of concurrent access to pkt_queue ?
>
> IIUC we should hold pkt_queue.lock when we call skb_queue_splice_init()
> and remove pkt_list_lock. (or hold pkt_list_lock when calling
> virtio_transport_purge_skbs, but pkt_list_lock seems useless now that
> we use skbuff)
>

In the previous patch was missing a hunk, new one attached:

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git fff5a5e7f528

--- a/net/vmw_vsock/vsock_loopback.c
+++ b/net/vmw_vsock/vsock_loopback.c
@@ -15,7 +15,6 @@
 struct vsock_loopback {
        struct workqueue_struct *workqueue;

-       spinlock_t pkt_list_lock; /* protects pkt_list */
        struct sk_buff_head pkt_queue;
        struct work_struct pkt_work;
 };
@@ -32,9 +31,7 @@ static int vsock_loopback_send_pkt(struct sk_buff *skb)
        struct vsock_loopback *vsock = &the_vsock_loopback;
        int len = skb->len;

-       spin_lock_bh(&vsock->pkt_list_lock);
        skb_queue_tail(&vsock->pkt_queue, skb);
-       spin_unlock_bh(&vsock->pkt_list_lock);

        queue_work(vsock->workqueue, &vsock->pkt_work);

@@ -113,9 +110,9 @@ static void vsock_loopback_work(struct work_struct *work)

        skb_queue_head_init(&pkts);

-       spin_lock_bh(&vsock->pkt_list_lock);
+       spin_lock_bh(&vsock->pkt_queue.lock);
        skb_queue_splice_init(&vsock->pkt_queue, &pkts);
-       spin_unlock_bh(&vsock->pkt_list_lock);
+       spin_unlock_bh(&vsock->pkt_queue.lock);

        while ((skb = __skb_dequeue(&pkts))) {
                virtio_transport_deliver_tap_pkt(skb);
@@ -132,7 +129,6 @@ static int __init vsock_loopback_init(void)
        if (!vsock->workqueue)
                return -ENOMEM;

-       spin_lock_init(&vsock->pkt_list_lock);
        skb_queue_head_init(&vsock->pkt_queue);
        INIT_WORK(&vsock->pkt_work, vsock_loopback_work);

@@ -156,9 +152,7 @@ static void __exit vsock_loopback_exit(void)

        flush_work(&vsock->pkt_work);

-       spin_lock_bh(&vsock->pkt_list_lock);
        virtio_vsock_skb_queue_purge(&vsock->pkt_queue);
-       spin_unlock_bh(&vsock->pkt_list_lock);

        destroy_workqueue(vsock->workqueue);
 }