netdev - Re: [PATCH net] tcp/dccp: fix lockdep issue when SYN is backlogged

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Date:   Mon, 01 Oct 2018 15:43:08 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net] tcp/dccp: fix lockdep issue when SYN is backlogged

From: Eric Dumazet <edumazet@...gle.com>
Date: Mon,  1 Oct 2018 15:02:26 -0700

> In normal SYN processing, packets are handled without listener
> lock and in RCU protected ingress path.
> 
> But syzkaller is known to be able to trick us and SYN
> packets might be processed in process context, after being
> queued into socket backlog.
> 
> In commit 06f877d613be ("tcp/dccp: fix other lockdep splats
> accessing ireq_opt") I made a very stupid fix, that happened
> to work mostly because of the regular path being RCU protected.
> 
> Really the thing protecting ireq->ireq_opt is RCU read lock,
> and the pseudo request refcnt is not relevant.
> 
> This patch extends what I did in commit 449809a66c1d ("tcp/dccp:
> block BH for SYN processing") by adding an extra rcu_read_{lock|unlock}
> pair in the paths that might be taken when processing SYN from
> socket backlog (thus possibly in process context)
> 
> Fixes: 06f877d613be ("tcp/dccp: fix other lockdep splats accessing ireq_opt")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>

Applied and queued up for -stable, thanks Eric.