netdev - Re: [PATCH net] net: netem: fix use after free and double free with packet corruption

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Message-Id: <20190614.190808.2204923376726716417.davem@davemloft.net>
Date:   Fri, 14 Jun 2019 19:08:08 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     jakub.kicinski@...ronome.com
Cc:     stephen@...workplumber.org, jhs@...atatu.com,
        xiyou.wangcong@...il.com, jiri@...nulli.us,
        netem@...ts.linux-foundation.org, netdev@...r.kernel.org,
        oss-drivers@...ronome.com, edumazet@...gle.com, posk@...gle.com
Subject: Re: [PATCH net] net: netem: fix use after free and double free
 with packet corruption

From: Jakub Kicinski <jakub.kicinski@...ronome.com>
Date: Wed, 12 Jun 2019 11:51:21 -0700

> Brendan reports that the use of netem's packet corruption capability
> leads to strange crashes.  This seems to be caused by
> commit d66280b12bd7 ("net: netem: use a list in addition to rbtree")
> which uses skb->next pointer to construct a fast-path queue of
> in-order skbs.
> 
> Packet corruption code has to invoke skb_gso_segment() in case
> of skbs in need of GSO.  skb_gso_segment() returns a list of
> skbs.  If next pointers of the skbs on that list do not get cleared
> fast path list goes into the weeds and tries to access the next
> segment skb multiple times.
> 
> Reported-by: Brendan Galloway <brendan.galloway@...ronome.com>
> Fixes: d66280b12bd7 ("net: netem: use a list in addition to rbtree")
> Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
> Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@...ronome.com>

Please rework the commit message a bit to make things cleared, your
ascii diagrams would be great. :)