linux-kernel - Re: Bug in net/ipv6/ip6_fib.c:fib6_dump

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Message-Id: <20120625.154047.462435723648654696.davem@davemloft.net>
Date:	Mon, 25 Jun 2012 15:40:47 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	johunt@...mai.com, kaber@...sh.net, dbavatar@...il.com,
	netdev@...r.kernel.org, yoshfuji@...ux-ipv6.org, jmorris@...ei.org,
	pekkas@...core.fi, kuznet@....inr.ac.ru,
	linux-kernel@...r.kernel.org, greearb@...delatech.com
Subject: Re: Bug in net/ipv6/ip6_fib.c:fib6_dump_table()

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Sat, 23 Jun 2012 07:37:31 +0200

> [PATCH] ipv6: fib: fix fib dump restart
> 
> Commit 2bec5a369ee79576a3 (ipv6: fib: fix crash when changing large fib
> while dumping it) introduced ability to restart the dump at tree root,
> but failed to skip correctly a count of already dumped entries. Code
> didn't match Patrick intent.
> 
> We must skip exactly the number of already dumped entries.
> 
> Note that like other /proc/net files or netlink producers, we could
> still dump some duplicates entries.
> 
> Reported-by: Debabrata Banerjee <dbavatar@...il.com>
> Reported-by: Josh Hunt <johunt@...mai.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

I've applied this.

But I wonder if it does the right thing, to be honest.

When tree change is detected, w->skip is set to w->count

But with your change, w->count won't be the number of entries to
skip from the root after the first time we handle a tree change.

So on the second tree change, we'll skip the wrong number of
entries, since the w->count we save into w->skip will be biased
by the previous w->skip value.  So we'll skip too few entries.

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