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

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Message-ID: <4C20D3A3.9010709@zytor.com>
Date:	Tue, 22 Jun 2010 08:15:47 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jiri Slaby <jirislaby@...il.com>
CC:	borislav.petkov@....com, x86@...nel.org,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: intel_cacheinfo: potential NULL dereference?

On 06/22/2010 04:20 AM, Jiri Slaby wrote:
> 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.
> 

Looks broken to me, indeed.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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