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Date: Mon, 18 Aug 2008 07:33:45 +0000
From: Jarek Poplawski <jarkao2@...il.com>
To: David Miller <davem@...emloft.net>
Cc: netdev@...r.kernel.org
Subject: Re: [PATCH]: Fix queueing return values...
On Sun, Aug 17, 2008 at 11:32:11PM -0700, David Miller wrote:
>
> I'm trying to make some further progress on this because it
> has been sitting for too long.
>
> What I want to do at this point is fix the most obvious
> problems in order to fix those crashes that were reported,
> and do it in such a way that an easy 2.6.26-stable backport
> is there too.
>
> After a first pass, just trying to sort out the worst cases,
> I came up with TBF and HTB that needed immediate fixes.
>
> HTB's case has been discussed to death before, and my current
> fix is greatly simplified from my original patch. I misread
> the logic and only that inner code block to the ->enqueue()
> and ->requeue() calls need to ensure proper return value
> propagation. I moved all kinds of things around for no good
> reason in my original patch.
>
> TBF is just a case of an improperly open-coded implementation
> of qdisc_reshape_fail() which corrupts the return value.
>
> First the net-2.6 version then the version intended for
> 2.6.26-stable submission:
>
> -------------------- net-2.6 --------------------
> pkt_sched: Fix return value corruption in HTB and TBF.
>
> Packet schedulers should only return NET_XMIT_DROP iff
> the packet really was dropped. If the packet does reach
> the device after we return NET_XMIT_DROP then TCP can
> crash because it depends upon the enqueue path return
> values being accurate.
I'm really happy I can see this patch at last, but it seems to miss
how it all begun, if you know what I mean:
http://marc.info/?l=linux-netdev&m=121768011703499&w=2
Jarek P.
>
> Signed-off-by: David S. Miller <davem@...emloft.net>
>
> diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
> index 6febd24..0df0df2 100644
> --- a/net/sched/sch_htb.c
> +++ b/net/sched/sch_htb.c
> @@ -577,7 +577,7 @@ static int htb_enqueue(struct sk_buff *skb, struct Qdisc *sch)
> sch->qstats.drops++;
> cl->qstats.drops++;
> }
> - return NET_XMIT_DROP;
> + return ret;
> } else {
> cl->bstats.packets +=
> skb_is_gso(skb)?skb_shinfo(skb)->gso_segs:1;
> @@ -623,7 +623,7 @@ static int htb_requeue(struct sk_buff *skb, struct Qdisc *sch)
> sch->qstats.drops++;
> cl->qstats.drops++;
> }
> - return NET_XMIT_DROP;
> + return ret;
> } else
> htb_activate(q, cl);
>
> diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
> index 7d3b7ff..94c6159 100644
> --- a/net/sched/sch_tbf.c
> +++ b/net/sched/sch_tbf.c
> @@ -123,15 +123,8 @@ static int tbf_enqueue(struct sk_buff *skb, struct Qdisc* sch)
> struct tbf_sched_data *q = qdisc_priv(sch);
> int ret;
>
> - if (qdisc_pkt_len(skb) > q->max_size) {
> - sch->qstats.drops++;
> -#ifdef CONFIG_NET_CLS_ACT
> - if (sch->reshape_fail == NULL || sch->reshape_fail(skb, sch))
> -#endif
> - kfree_skb(skb);
> -
> - return NET_XMIT_DROP;
> - }
> + if (qdisc_pkt_len(skb) > q->max_size)
> + return qdisc_reshape_fail(skb, sch);
>
> ret = qdisc_enqueue(skb, q->qdisc);
> if (ret != 0) {
>
> -------------------- 2.6.26-stable --------------------
> pkt_sched: Fix return value corruption in HTB and TBF.
>
> Packet schedulers should only return NET_XMIT_DROP iff
> the packet really was dropped. If the packet does reach
> the device after we return NET_XMIT_DROP then TCP can
> crash because it depends upon the enqueue path return
> values being accurate.
>
> Signed-off-by: David S. Miller <davem@...emloft.net>
>
> diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
> index 3fb58f4..51c3f68 100644
> --- a/net/sched/sch_htb.c
> +++ b/net/sched/sch_htb.c
> @@ -595,11 +595,13 @@ static int htb_enqueue(struct sk_buff *skb, struct Qdisc *sch)
> kfree_skb(skb);
> return ret;
> #endif
> - } else if (cl->un.leaf.q->enqueue(skb, cl->un.leaf.q) !=
> + } else if ((ret = cl->un.leaf.q->enqueue(skb, cl->un.leaf.q)) !=
> NET_XMIT_SUCCESS) {
> - sch->qstats.drops++;
> - cl->qstats.drops++;
> - return NET_XMIT_DROP;
> + if (ret == NET_XMIT_DROP) {
> + sch->qstats.drops++;
> + cl->qstats.drops++;
> + }
> + return ret;
> } else {
> cl->bstats.packets +=
> skb_is_gso(skb)?skb_shinfo(skb)->gso_segs:1;
> @@ -639,11 +641,13 @@ static int htb_requeue(struct sk_buff *skb, struct Qdisc *sch)
> kfree_skb(skb);
> return ret;
> #endif
> - } else if (cl->un.leaf.q->ops->requeue(skb, cl->un.leaf.q) !=
> + } else if ((ret = cl->un.leaf.q->ops->requeue(skb, cl->un.leaf.q)) !=
> NET_XMIT_SUCCESS) {
> - sch->qstats.drops++;
> - cl->qstats.drops++;
> - return NET_XMIT_DROP;
> + if (ret == NET_XMIT_DROP) {
> + sch->qstats.drops++;
> + cl->qstats.drops++;
> + }
> + return ret;
> } else
> htb_activate(q, cl);
>
> diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
> index 0b7d78f..fc6f8f3 100644
> --- a/net/sched/sch_tbf.c
> +++ b/net/sched/sch_tbf.c
> @@ -123,15 +123,8 @@ static int tbf_enqueue(struct sk_buff *skb, struct Qdisc* sch)
> struct tbf_sched_data *q = qdisc_priv(sch);
> int ret;
>
> - if (skb->len > q->max_size) {
> - sch->qstats.drops++;
> -#ifdef CONFIG_NET_CLS_ACT
> - if (sch->reshape_fail == NULL || sch->reshape_fail(skb, sch))
> -#endif
> - kfree_skb(skb);
> -
> - return NET_XMIT_DROP;
> - }
> + if (skb->len > q->max_size)
> + return qdisc_reshape_fail(skb, sch);
>
> if ((ret = q->qdisc->enqueue(skb, q->qdisc)) != 0) {
> sch->qstats.drops++;
> --------------------
--
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