linux-kernel - Re: [held lock freed] Re: [GIT] Networking

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Message-Id: <201103211622.40851.arnd@arndb.de>
Date:	Mon, 21 Mar 2011 16:22:40 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, 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

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;
 }
 
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