linux-kernel - Re: [PATCH] ISDN: Avoid a potential NULL ptr deref in ippp

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Pine.LNX.4.64N.0611211211280.25455@attu4.cs.washington.edu>
Date:	Tue, 21 Nov 2006 12:20:30 -0800 (PST)
From:	David Rientjes <rientjes@...washington.edu>
To:	Jesper Juhl <jesper.juhl@...il.com>
cc:	linux-kernel@...r.kernel.org,
	Michael Hipp <Michael.Hipp@...dent.uni-tuebingen.de>,
	Karsten Keil <kkeil@...e.de>,
	Kai Germaschewski <kai.germaschewski@....de>,
	isdn4linux@...tserv.isdn4linux.de, starvik@...s.com,
	dev-etrax@...s.com
Subject: Re: [PATCH] ISDN: Avoid a potential NULL ptr deref in ippp

On Tue, 21 Nov 2006, Jesper Juhl wrote:

> Any reason why we can't apply the patch below?
> 
> On 30/10/06, Jesper Juhl <jesper.juhl@...il.com> wrote:
> >
> > There's a potential problem in isdn_ppp.c::isdn_ppp_decompress().
> > dev_alloc_skb() may fail and return NULL. If it does we will be passing a
> > NULL skb_out to ipc->decompress() and may also end up
> > dereferencing a NULL pointer at
> >     *proto = isdn_ppp_strip_proto(skb_out);
> > Correct this by testing 'skb_out' against NULL early and bail out.
> >
> >
> > Signed-off-by: Jesper Juhl <jesper.juhl@...il.com>
> > ---
> >
> >  drivers/isdn/i4l/isdn_ppp.c |    5 +++++
> >  1 files changed, 5 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/isdn/i4l/isdn_ppp.c b/drivers/isdn/i4l/isdn_ppp.c
> > index 119412d..5a97ce6 100644
> > --- a/drivers/isdn/i4l/isdn_ppp.c
> > +++ b/drivers/isdn/i4l/isdn_ppp.c
> > @@ -2536,6 +2536,11 @@ static struct sk_buff *isdn_ppp_decompre
> >                 rsparm.maxdlen = IPPP_RESET_MAXDATABYTES;
> >
> >                 skb_out = dev_alloc_skb(is->mru + PPP_HDRLEN);
> > +               if (!skb_out) {
> > +                       kfree_skb(skb);
> > +                       printk(KERN_ERR "ippp: decomp memory allocation
> > failure\n");
> > +                       return NULL;
> > +               }
> >                 len = ipc->decompress(stat, skb, skb_out, &rsparm);
> >                 kfree_skb(skb);
> >                 if (len <= 0) {
> >
> 

I'm not sure that there's a problem with the original code.  If skb_out 
cannot be allocated, the ipc->decompress function should return NULL 
because struct ippp_struct *master would have been passed as NULL.  So len 
would be 0 upon return, skb would be freed, and the following switch 
statement would catch the error.  Notice it's not a bug to pass NULL to 
kfree_skb() later.

		David
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/