Subject: Re: [regression] nf_iterate(), BUG: unable to handle kernel NULL
	pointer dereference
From: Matt Mackall <mpm@selenic.com>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>, Patrick McHardy <kaber@trash.net>,
       Ingo Molnar <mingo@elte.hu>, David Miller <davem@davemloft.net>,
       w@1wt.eu, davidn@davidnewall.com, torvalds@linux-foundation.org,
       akpm@linux-foundation.org, netdev@vger.kernel.org,
       linux-kernel@vger.kernel.org, stefanr@s5r6.in-berlin.de, rjw@sisk.pl,
       ilpo.jarvinen@helsinki.fi, Dave Jones <davej@redhat.com>,
       Christoph Lameter <cl@linux-foundation.org>
In-Reply-To: <20080725013958.GA14200@gondor.apana.org.au>
References: <20080724093411.GA12001@elte.hu>
	 <20080724115625.GA23994@elte.hu> <20080724115957.GA25701@elte.hu>
	 <48886FA6.6050908@trash.net> <20080724122203.GA7187@gondor.apana.org.au>
	 <84144f020807240540vbe7ef50uee2cacabe8016546@mail.gmail.com>
	 <20080724125004.GA7426@gondor.apana.org.au>
	 <1216905109.15519.200.camel@calx>
	 <20080724143706.GA8461@gondor.apana.org.au>
	 <1216921639.15519.239.camel@calx>
	 <20080725013958.GA14200@gondor.apana.org.au>
Content-Type: text/plain
Date: Thu, 24 Jul 2008 21:59:33 -0500
Message-Id: <1216954773.15519.261.camel@calx>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1388
Lines: 34


On Fri, 2008-07-25 at 09:39 +0800, Herbert Xu wrote:
> On Thu, Jul 24, 2008 at 12:47:19PM -0500, Matt Mackall wrote:
> >
> > Let's try this again: did you know that ksize could fail depending on
> > kernel configuration? Most of us would answer no. That suggests the API
> > is bad. This ranks 12 on Rusty's spectrum of user-friendly APIs:
> 
> I think you misunderstood my argument.  I never suggested changing
> the existing ksize interface to return an error onto unsuspecting
> users.  I suggested creating a new interface that is explicitly
> designed to return an error if the underlying implementation
> is unable to support this.

I think that could probably be made to work. Perhaps something like:

size_t kmalloc_extra(void *); /* how many extra bytes in this kmalloc?
*/

Which, if it didn't work, could return a nice safe 0. We could argue
about signedness a bit, but I think this would always be safe.

This will also work with all our current kmalloc implementations. The
trouble was calling ksize() on kmem_cache_alloc objects, which happens
to work with SLAB and SLOB.

-- 
Mathematics is the supreme nostalgia of our time.

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