netdev - Re: [PATCH net v2] netfilter: drop outermost socket lock in getsockopt()

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Date:   Wed, 14 Feb 2018 20:44:24 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Florian Westphal <fw@...len.de>,
        Xin Long <lucien.xin@...il.com>,
        netfilter-devel@...r.kernel.org
Subject: Re: [PATCH net v2] netfilter: drop outermost socket lock in
 getsockopt()

On Thu, Feb 08, 2018 at 12:19:00PM +0100, Paolo Abeni wrote:
> The Syzbot reported a possible deadlock in the netfilter area caused by
> rtnl lock, xt lock and socket lock being acquired with a different order
> on different code paths, leading to the following backtrace:
> 
> ======================================================
> WARNING: possible circular locking dependency detected
> 4.15.0+ #301 Not tainted
> ------------------------------------------------------
> syzkaller233489/4179 is trying to acquire lock:
>   (rtnl_mutex){+.+.}, at: [<0000000048e996fd>] rtnl_lock+0x17/0x20
> net/core/rtnetlink.c:74
> 
> but task is already holding lock:
>   (&xt[i].mutex){+.+.}, at: [<00000000328553a2>]
> xt_find_table_lock+0x3e/0x3e0 net/netfilter/x_tables.c:1041
> 
> which lock already depends on the new lock.
> ===
> 
> Since commit 3f34cfae1230 ("netfilter: on sockopt() acquire sock lock
> only in the required scope"), we already acquire the socket lock in
> the innermost scope, where needed. In such commit I forgot to remove
> the outer-most socket lock from the getsockopt() path, this commit
> addresses the issues dropping it now.

Applied, thanks.