netdev - Re: [patch] Fix handling of overlength pathname in AF_UNIX sun

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Date:	Wed, 18 Apr 2012 10:13:18 -0300
From:	Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	"Carlos O'Donell" <carlos@...temhalted.org>,
	David Miller <davem@...emloft.net>, mtk.manpages@...il.com,
	netdev@...r.kernel.org, penguin-kernel@...ove.sakura.ne.jp,
	linux-api@...r.kernel.org, yoshfuji@...ux-ipv6.org,
	jengelh@...ozas.de, w@....eu, alan@...rguk.ukuu.org.uk
Subject: Re: [patch] Fix handling of overlength pathname in AF_UNIX sun_path

On Wed, Apr 18, 2012 at 09:17:26AM +0100, David Laight wrote:
> 
> > 
> > Why not have:
> > 
> > diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> > index d510353..f9f77a7 100644
> > --- a/net/unix/af_unix.c
> > +++ b/net/unix/af_unix.c
> > @@ -216,6 +216,9 @@ static int unix_mkname(struct sockaddr_un
> > *sunaddr, int len, unsigned *hashp)
> >                  */
> >                 ((char *)sunaddr)[len] = 0;
> >                 len = strlen(sunaddr->sun_path)+1+sizeof(short);
> > +               /* No null terminator was found in the path. */
> > +               if (len > sizeof(*sunaddr))
> > +                       return -EINVAL;
> >                 return len;
> 
> That could generate a kernel page fault!
> (Depending on what follows (or rather doesn't follow!) sun_path.)
> You'd need to use memchr() not strlen().
> 
> 	David
> 

Hi, David.

What follows is a 0 byte, because it's set that way in the line before
strlen. Note that len is tested for sizeof(*sunaddr), and there is a
huge comment about that extra byte that was omitted.

The whole function is at net/unix/af_unix.c:203.

Regards,
Cascardo.

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