netdev - Re: problem with 'net: Partially allow skb destructors to be used on receive path'

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Message-Id: <20091202.160009.232607094.davem@davemloft.net>
Date:	Wed, 02 Dec 2009 16:00:09 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	socketcan@...tkopp.net
Cc:	herbert@...dor.apana.org.au, matthias.fuchs@....eu,
	netdev@...r.kernel.org, mma@...ectxp.com
Subject: Re: problem with 'net: Partially allow skb destructors to be used
 on receive path'

From: Oliver Hartkopp <socketcan@...tkopp.net>
Date: Wed, 02 Dec 2009 22:21:44 +0100

> after a request from Matthias Fuchs regarding the status of this patch in
> 2.6.30-stable, i discovered a problem with the commit in 2.6.30-stable:
> 
> Patch discussion/history: http://patchwork.ozlabs.org/patch/28993/
> 
> The commit in mainline is correct:
 ...
> But the commit in the 2.6.30-stable tree
> 
> http://git.kernel.org/?p=linux/kernel/git/stable/linux-2.6.30.y.git;a=commitdiff;h=172570a224fe66d560c097e48fca15b620c76e72
> 
> has a problem in patching include/net/sock.h:
 ...
> The skb_orphan(skb) in skb_set_owner_w() is missing here.
> 
> Is there any chance to fix that in 2.6.30-stable?

Thanks for catching this.  I hate patch :-/

I'll send a fixup patch to the -stable folks right now.

Thanks again!

net: Fix thinko in backport of skb destructor fix.

As noticed by Oliver Hartkopp, the backport of the
'net: Partially allow skb destructors to be used on receive path'
(2.6.30.y commit: 172570a224fe66d560c097e48fca15b620c76e72,
 upstream commit: d55d87fdff8252d0e2f7c28c2d443aee17e9d70f)
was buggy.

It should have added an skb_orphan() call to both skb_set_owner_w()
and skb_set_owner_r().  Instead it added two calls to skb_set_owner_r().

This fixed it up.

Signed-off-by: David S. Miller <davem@...emloft.net>

diff --git a/include/net/sock.h b/include/net/sock.h
index 9bc2c83..cda3801 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1223,6 +1223,7 @@ static inline int skb_copy_to_page(struct sock *sk, char __user *from,
 
 static inline void skb_set_owner_w(struct sk_buff *skb, struct sock *sk)
 {
+	skb_orphan(skb);
 	sock_hold(sk);
 	skb->sk = sk;
 	skb->destructor = sock_wfree;
@@ -1232,7 +1233,6 @@ static inline void skb_set_owner_w(struct sk_buff *skb, struct sock *sk)
 static inline void skb_set_owner_r(struct sk_buff *skb, struct sock *sk)
 {
 	skb_orphan(skb);
-	skb_orphan(skb);
 	skb->sk = sk;
 	skb->destructor = sock_rfree;
 	atomic_add(skb->truesize, &sk->sk_rmem_alloc);
--
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