netdev - Re: [PATCH net] tcp/dccp: remove reqsk_put() from inet_child

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Date:   Tue, 12 Sep 2017 20:39:14 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     sp3485@...umbia.edu, netdev@...r.kernel.org,
        xiyou.wangcong@...il.com, andrew.aday@...umbia.edu
Subject: Re: [PATCH net] tcp/dccp: remove reqsk_put() from
 inet_child_forget()

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Mon, 11 Sep 2017 15:58:38 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Back in linux-4.4, I inadvertently put a call to reqsk_put() in
> inet_child_forget(), forgetting it could be called from two different
> points.
> 
> In the case it is called from inet_csk_reqsk_queue_add(), we want to
> keep the reference on the request socket, since it is released later by
> the caller (tcp_v{4|6}_rcv())
> 
> This bug never showed up because atomic_dec_and_test() was not signaling
> the underflow, and SLAB_DESTROY_BY RCU semantic for request sockets
> prevented the request to be put in quarantine.
> 
> Recent conversion of socket refcount from atomic_t to refcount_t finally
> exposed the bug.
> 
> So move the reqsk_put() to inet_csk_listen_stop() to fix this.
> 
> Thanks to Shankara Pailoor for using syzkaller and providing
> a nice set of .config and C repro.
 ...
> Fixes: ebb516af60e1 ("tcp/dccp: fix race at listener dismantle phase")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Shankara Pailoor <sp3485@...umbia.edu>
> Tested-by: Shankara Pailoor <sp3485@...umbia.edu>

Applied and queued up for -stable.

Thanks.