netdev - Re: [Patch net] qrtr: orphan skb before queuing in xmit

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Message-ID: <590b7621-95bf-1220-f786-783996fd4a4c@gmail.com>
Date:   Thu, 23 Jul 2020 22:35:09 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
Cc:     syzbot+6720d64f31c081c2f708@...kaller.appspotmail.com,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [Patch net] qrtr: orphan skb before queuing in xmit



On 7/23/20 9:50 PM, Cong Wang wrote:
> Similar to tun_net_xmit(), we have to orphan the skb
> before queuing it, otherwise we may use the socket when
> purging the queue after it is freed by user-space.

Which socket ?

By not calling skb_orphan(skb), this skb should own a reference on skb->sk preventing
skb->sk to disappear.

It seems that instead of skb_orphan() here, we could avoid calling skb_set_owner_w() in the first place,
because this is confusing.

Also, there seems to be no limit on number of skbs that can be queued, this looks rather dangerous.



diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c
index 0cb4adfc6641da0b1add7a8b40957fd23df1e075..9b180768dbfe9ea100ad008d92522e340f73101e 100644
--- a/net/qrtr/qrtr.c
+++ b/net/qrtr/qrtr.c
@@ -661,7 +661,6 @@ static void qrtr_port_remove(struct qrtr_sock *ipc)
                pkt->client.node = cpu_to_le32(ipc->us.sq_node);
                pkt->client.port = cpu_to_le32(ipc->us.sq_port);
 
-               skb_set_owner_w(skb, &ipc->sk);
                qrtr_bcast_enqueue(NULL, skb, QRTR_TYPE_DEL_CLIENT, &ipc->us,
                                   &to);
        }
@@ -855,7 +854,6 @@ static int qrtr_bcast_enqueue(struct qrtr_node *node, struct sk_buff *skb,
                skbn = skb_clone(skb, GFP_KERNEL);
                if (!skbn)
                        break;
-               skb_set_owner_w(skbn, skb->sk);
                qrtr_node_enqueue(node, skbn, type, from, to);
        }
        mutex_unlock(&qrtr_node_lock);


> 
> Reported-and-tested-by: syzbot+6720d64f31c081c2f708@...kaller.appspotmail.com
> Fixes: 28fb4e59a47d ("net: qrtr: Expose tunneling endpoint to user space")
> Cc: Bjorn Andersson <bjorn.andersson@...aro.org>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> ---
>  net/qrtr/tun.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/qrtr/tun.c b/net/qrtr/tun.c
> index 15ce9b642b25..54a565dcfef3 100644
> --- a/net/qrtr/tun.c
> +++ b/net/qrtr/tun.c
> @@ -20,6 +20,7 @@ static int qrtr_tun_send(struct qrtr_endpoint *ep, struct sk_buff *skb)
>  {
>  	struct qrtr_tun *tun = container_of(ep, struct qrtr_tun, ep);
>  
> +	skb_orphan(skb);
>  	skb_queue_tail(&tun->queue, skb);
>  
>  	/* wake up any blocking processes, waiting for new data */
>