linux-kernel - Re: commit f5f99309 (sock: do not set sk_err in sock_dequeue_err

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Date:   Thu, 1 Jun 2017 10:39:26 -0400
From:   Soheil Hassas Yeganeh <soheil@...gle.com>
To:     Cyril Hrubis <chrubis@...e.cz>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Shmulik Ladkani <shmulik.ladkani@...il.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Pravin B Shelar <pshelar@....org>,
        Eric Dumazet <edumazet@...gle.com>,
        WANG Cong <xiyou.wangcong@...il.com>,
        Yaogong Wang <wygivan@...gle.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        netdev <netdev@...r.kernel.org>, linux-kernel@...r.kernel.org
Subject: Re: commit f5f99309 (sock: do not set sk_err in sock_dequeue_err_skb)
 has broken ping

On Thu, Jun 1, 2017 at 10:31 AM, Cyril Hrubis <chrubis@...e.cz> wrote:
> I've started bisecting on v4.11 and see the problem on v4.10 on another
> machine, the patch should be there in both cases and the bug is easily
> reproducible.

Thank you for the confirmation. Could you please try the following
patch to see if it fixes your issue?

>From 3ec438460425d127741b20f03f78644c9e441e8c Mon Sep 17 00:00:00 2001
From: Soheil Hassas Yeganeh <soheil@...gle.com>
Date: Thu, 1 Jun 2017 10:34:09 -0400
Subject: [PATCH net] sock: reset sk_err when the error queue is empty

Before f5f99309fa74 (sock: do not set sk_err in
sock_dequeue_err_skb), sk_err was reset to 0 upon reading
from the error queue when the error queue was empty.

Applications, most notably ping, are relying on this
behavior to reset sk_err.

Reset sk_err when there is no packet left on the
error queue.

Fixes: f5f99309fa74 (sock: do not set sk_err in sock_dequeue_err_skb)
Reported-by: Cyril Hrubis <chrubis@...e.cz>
Signed-off-by: Soheil Hassas Yeganeh <soheil@...gle.com>
---
 net/core/skbuff.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 346d3e85dfbc..5a726161f4e4 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3758,7 +3758,7 @@ struct sk_buff *sock_dequeue_err_skb(struct sock *sk)
  icmp_next = is_icmp_err_skb(skb_next);
  spin_unlock_irqrestore(&q->lock, flags);

- if (is_icmp_err_skb(skb) && !icmp_next)
+ if ((is_icmp_err_skb(skb) && !icmp_next) || !skb_next)
  sk->sk_err = 0;

  if (skb_next)
-- 
2.13.0.219.gdb65acc882-goog


>> 2. I've also have sent a fix to iputils on
>> https://github.com/iputils/iputils/pull/75. Would you be kind to try
>> that pull request as well?
>
> That fixed the problem, you can add:
>
> Tested-by: Cyril Hrubis <chrubis@...e.cz>

Thank you for testing! Will do.