netdev - Re: [held lock freed] Re: [GIT] Networking

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Message-ID: <20110321161627.GB28580@elte.hu>
Date:	Mon, 21 Mar 2011 17:16:27 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [held lock freed] Re: [GIT] Networking


* Arnd Bergmann <arnd@...db.de> wrote:

> On Monday 21 March 2011, Eric Dumazet wrote:
> > > diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c
> > > index 4680b1e..b2cf1db 100644
> > > --- a/net/x25/af_x25.c
> > > +++ b/net/x25/af_x25.c
> > > @@ -669,8 +669,8 @@ static int x25_release(struct socket *sock)
> > >  
> > >       sock_orphan(sk);
> > >  out:
> > > -     release_sock(sk);
> > >       sock_put(sk);
> > > +     release_sock(sk);
> > >       return 0;
> > >  }
> > >  
> > 
> > Hmm, x25_release() looks fine, I believe no fix is needed.
> > 
> 
> D'oh. You're right of course. My patch would introduce the bug,
> not fix it. Updated patch below.
> 
> 	Arnd
> 8<-------------------------
> net/appletalk: fix atalk_release use after free
> 
> The BKL removal in appletalk introduced a use-after-free problem,
> where atalk_destroy_socket frees a sock, but we still release
> the socket lock on it.
> 
> An easy fix is to take an extra reference on the sock and sock_put
> it when returning from atalk_release.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> 
> index 3d4f4b0..206e771 100644
> --- a/net/appletalk/ddp.c
> +++ b/net/appletalk/ddp.c
> @@ -1051,6 +1051,7 @@ static int atalk_release(struct socket *sock)
>  {
>  	struct sock *sk = sock->sk;
>  
> +	sock_hold(sk);
>  	lock_sock(sk);
>  	if (sk) {
>  		sock_orphan(sk);
> @@ -1058,6 +1059,8 @@ static int atalk_release(struct socket *sock)
>  		atalk_destroy_socket(sk);
>  	}
>  	release_sock(sk);
> +	sock_put(sk);
> +
>  	return 0;
>  }

I have not triggered the lockdep warning in this code yet - but i've ran the 
patch and have seen no ill effects from it so far.

Thanks,

	Ingo
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