linux-kernel - Re: intel_cacheinfo: potential NULL dereference?

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Date:	Tue, 22 Jun 2010 15:08:25 +0200
From:	Borislav Petkov <bp@...64.org>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: intel_cacheinfo: potential NULL dereference?

From: Jiri Slaby <jirislaby@...il.com>
Date: Tue, Jun 22, 2010 at 07:20:14AM -0400

> On 06/22/2010 01:18 PM, Jiri Slaby wrote:
> > Hi,
> > 
> > commit 9350f982 changed the code so it looks like:
> > static ssize_t store_cache_disable(struct _cpuid4_info *this_leaf,
> >                                    const char *buf, size_t count,
> >                                    unsigned int slot)
> > {
> >         struct pci_dev *dev = this_leaf->l3->dev;   <<1>>
> >         int cpu = cpumask_first(to_cpumask(this_leaf->shared_cpu_map));
> >         unsigned long val = 0;
> > 
> > #define SUBCACHE_MASK   (3UL << 20)
> > #define SUBCACHE_INDEX  0xfff
> > 
> >         if (!this_leaf->l3 || !this_leaf->l3->can_disable)  <<2>>
> >                 return -EINVAL;
> > 
> > Stanse found, that this_leaf->l3 is dereferenced at <<1>>, but checked
> > for being NULL at <<2>>. Is the check superfluous or the dev assignment
> > should go after the check?
> 
> Oh, and I have another report with same symptoms for show_cache_disable.

Right, so I have a patch in tip/x86/cpu
(8cc1176e5de534d55cb26ff0cef3fd0d6ad8c3c0) which reorganizes
and cleans up that code. With it, all possible checks land in
amd_check_l3_disable() and if they have all been passed, the PCI dev is
guaranteed to be properly set. So no need for sprinkling additional NULL
checks in the code.

How's that?

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
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