netdev - Re: [PATCH net] net: increment xmit_recursion level in dev_direct

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Date:   Thu, 18 Jun 2020 20:48:30 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com, kuba@...nel.org,
        syzkaller@...glegroups.com
Subject: Re: [PATCH net] net: increment xmit_recursion level in
 dev_direct_xmit()

From: Eric Dumazet <edumazet@...gle.com>
Date: Wed, 17 Jun 2020 22:23:25 -0700

> Back in commit f60e5990d9c1 ("ipv6: protect skb->sk accesses
> from recursive dereference inside the stack") Hannes added code
> so that IPv6 stack would not trust skb->sk for typical cases
> where packet goes through 'standard' xmit path (__dev_queue_xmit())
> 
> Alas af_packet had a dev_direct_xmit() path that was not
> dealing yet with xmit_recursion level.
> 
> Also change sk_mc_loop() to dump a stack once only.
> 
> Without this patch, syzbot was able to trigger :
 ...
> f60e5990d9c1 ("ipv6: protect skb->sk accesses from recursive dereference inside the stack")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>

Applied and queued up for -stable.

I only noticed after pushing this out the missing "Fixes: " prefix, but not
much I can do about this now sorry :-/