linux-kernel - Re: [PATCHv2] tcp: fix crash in tcp_xmit_retransmit

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Date:	Mon, 19 Jul 2010 16:09:15 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Cc:	Lennart Schulte <lennart.schulte@...s.rwth-aachen.de>,
	David Miller <davem@...emloft.net>, Tejun Heo <tj@...nel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Fehrmann, Henning" <henning.fehrmann@....mpg.de>,
	Carsten Aulbert <carsten.aulbert@....mpg.de>
Subject: Re: [PATCHv2] tcp: fix crash in tcp_xmit_retransmit_queue

Le lundi 19 juillet 2010 à 14:16 +0300, Ilpo Järvinen a écrit :

> Thanks for testing.
> 
> DaveM, I think this oops was introduced for 2.6.28 (in 
> 08ebd1721ab8fd362e90ae17b461c07b23fa2824 it seems, to be exact) so to 
> stables it should go too please. I've only tweaked the message (so no need 
> for Lennart to retest v2 :-)).
> 
> --
> [PATCHv2] tcp: fix crash in tcp_xmit_retransmit_queue
> 
> It can happen that there are no packets in queue while calling
> tcp_xmit_retransmit_queue(). tcp_write_queue_head() then returns
> NULL and that gets deref'ed to get sacked into a local var.
> 
> There is no work to do if no packets are outstanding so we just
> exit early.
> 
> This oops was introduced by 08ebd1721ab8fd (tcp: remove tp->lost_out
> guard to make joining diff nicer).
> 

But prior to commit 08ebd1721ab8fd3, we were not testing
tp->packets_out, but tp->lost_out

if it was 0, we were not doing the tcp_for_write_queue_from() loop.

Not sure it makes a difference ?

> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
> Reported-by: Lennart Schulte <lennart.schulte@...s.rwth-aachen.de>
> Tested-by: Lennart Schulte <lennart.schulte@...s.rwth-aachen.de>
> ---
>  net/ipv4/tcp_output.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index b4ed957..7ed9dc1 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -2208,6 +2208,9 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
>  	int mib_idx;
>  	int fwd_rexmitting = 0;
>  
> +	if (!tp->packets_out)
> +		return;
> +
>  	if (!tp->lost_out)
>  		tp->retransmit_high = tp->snd_una;
>  


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