linux-kernel - Re: use-after-free in sock_wake

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Message-ID: <CANn89iK9PHPUMwYf=ns=mW2yigx56jQtOOhOzKihMr5RCZ0hRw@mail.gmail.com>
Date:	Tue, 24 Nov 2015 14:12:35 -0800
From:	Eric Dumazet <edumazet@...gle.com>
To:	Benjamin LaHaise <bcrl@...ck.org>
Cc:	Jason Baron <jbaron@...mai.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	David Howells <dhowells@...hat.com>,
	Ying Xue <ying.xue@...driver.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Rainer Weikusat <rweikusat@...ileactivedefense.com>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: use-after-free in sock_wake_async

On Tue, Nov 24, 2015 at 2:03 PM, Eric Dumazet <edumazet@...gle.com> wrote:

>
> This might be a data race in sk_wake_async() if inlined by compiler
> (see https://lkml.org/lkml/2015/11/24/680 for another example)
>
> KASAN adds register pressure and compiler can then do 'stupid' things :(
>
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 7f89e4ba18d1..2af6222ccc67 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -2008,7 +2008,7 @@ static inline unsigned long sock_wspace(struct sock *sk)
>  static inline void sk_wake_async(struct sock *sk, int how, int band)
>  {
>         if (sock_flag(sk, SOCK_FASYNC))
> -               sock_wake_async(sk->sk_socket, how, band);
> +               sock_wake_async(READ_ONCE(sk->sk_socket), how, band);
>  }
>
>  /* Since sk_{r,w}mem_alloc sums skb->truesize, even a small frame might

Oh well, sock_wake_async() can not be inlined, scratch this.
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