netdev - Re: [PATCH -next v2] unix stream: Fix use-after-free crashes

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Date:	Wed, 07 Sep 2011 07:08:20 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Yan, Zheng" <yanzheng@...n.com>
Cc:	Tim Chen <tim.c.chen@...ux.intel.com>,
	"Yan, Zheng" <zheng.z.yan@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
	"jirislaby@...il.com" <jirislaby@...il.com>,
	"sedat.dilek@...il.com" <sedat.dilek@...il.com>, alex.shi@...el.com
Subject: Re: [PATCH -next v2] unix stream: Fix use-after-free crashes

Le mercredi 07 septembre 2011 à 12:36 +0800, Yan, Zheng a écrit :

> I guess you misunderstood this code. Set scm_ref to false means skb will inherit
> sender's reference. Then we call unix_scm_to_skb() with parameter
> 'ref' == false.
> So it doesn't get additional reference. I admit my patch is confusing,
> but I think
> Tim's new patch is OK. (even in the case of fail skb allocation or
> user->kernel copy)
> 

I want to be able to review the code now, and in two or three years too,
without spending hours and hours.

Could you _please_ guys send a patch, with :

1) A good changelog : In this confusing area, this is probably more
important than actual code.

2) right logic and right variable names

I am sorry, but this is not good :

+               /* encode scm in skb and use the scm ref */
+               ref_avail = false;
+               if (sent + size < len) { 
+                       /* Only send the fds in the first buffer */
+                       /* get additional ref if more skbs will be created */
+                       err = unix_scm_to_skb(siocb->scm, skb, !fds_sent, true);
+                       ref_avail = true;
+               } else
+                       err = unix_scm_to_skb(siocb->scm, skb, !fds_sent, false);




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