netdev - Re: [PATCH net] tcp: do not leave dangling pointers in tp->highest

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Date:   Fri, 24 Jan 2020 09:10:19 +0100 (CET)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        cambda@...ux.alibaba.com, ycheng@...gle.com, ncardwell@...gle.com
Subject: Re: [PATCH net] tcp: do not leave dangling pointers in
 tp->highest_sack

From: Eric Dumazet <edumazet@...gle.com>
Date: Wed, 22 Jan 2020 21:03:00 -0800

> Latest commit 853697504de0 ("tcp: Fix highest_sack and highest_sack_seq")
> apparently allowed syzbot to trigger various crashes in TCP stack [1]
> 
> I believe this commit only made things easier for syzbot to find
> its way into triggering use-after-frees. But really the bugs
> could lead to bad TCP behavior or even plain crashes even for
> non malicious peers.
> 
> I have audited all calls to tcp_rtx_queue_unlink() and
> tcp_rtx_queue_unlink_and_free() and made sure tp->highest_sack would be updated
> if we are removing from rtx queue the skb that tp->highest_sack points to.
> 
> These updates were missing in three locations :
> 
> 1) tcp_clean_rtx_queue() [This one seems quite serious,
>                           I have no idea why this was not caught earlier]
> 
> 2) tcp_rtx_queue_purge() [Probably not a big deal for normal operations]
> 
> 3) tcp_send_synack()     [Probably not a big deal for normal operations]
> 
> [1]
 ...
> Fixes: 853697504de0 ("tcp: Fix highest_sack and highest_sack_seq")
> Fixes: 50895b9de1d3 ("tcp: highest_sack fix")
> Fixes: 737ff314563c ("tcp: use sequence distance to detect reordering")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied and queued up for -stable, thanks.