linux-kernel - Re: [PATCH 1/1] ipv4: off-by-one in continuation handling in /proc/net/route

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Date:	Thu, 13 Aug 2015 08:10:58 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Andy Whitcroft <apw@...onical.com>,
	Alexander Duyck <alexander.h.duyck@...hat.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] ipv4: off-by-one in continuation handling in
 /proc/net/route

On Thu, 2015-08-13 at 11:21 +0100, Andy Whitcroft wrote:
> When generating /proc/net/route we emit a header followed by a line for
> each route.  When a short read is performed we will restart this process
> based on the open file descriptor.  When calculating the start point we
> fail to take into account that the 0th entry is the header.  This leads
> us to skip the first entry when doing a continuation read.
> 
> This can be easily seen with the comparison below:
> 
>   while read l; do echo "$l"; done </proc/net/route >A
>   cat /proc/net/route >B
>   diff -bu A B | grep '^[+-]'
> 
> On my example machine I have approximatly 10KB of route output.  There we
> see the very first non-title element is lost in the while read case,
> and an entry around the 8K mark in the cat case:
> 
>   +wlan0 00000000 02021EAC 0003 0 0 400 00000000 0 0 0
>   -tun1  00C0AC0A 00000000 0001 0 0 950 00C0FFFF 0 0 0
> 
> Fix up the off-by-one when reaquiring position on continuation.
> 
> BugLink: http://bugs.launchpad.net/bugs/1483440
> Signed-off-by: Andy Whitcroft <apw@...onical.com>
> ---
>  net/ipv4/fib_trie.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> 	From code inspection I belive this was introduced by the Fixes
> 	below, but I have not tested this to confirm.
> 
> 	Fixes: 8be33e955cb9 ("ipv4: off-by-one in continuation handling in /proc/net/route")

You probably meant

Fixes: 8be33e955cb9 ("fib_trie: Fib walk rcu should take a tnode and key instead of a trie and a leaf")

CC Alexander for review/comment


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