linux-kernel - Re: [PATCH] scatterlist: prevent invalid free when alloc fails

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Message-ID: <4C784B04.7060604@kernel.org>
Date:	Sat, 28 Aug 2010 01:32:20 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Jeffrey Carlyle <jeff.carlyle@...orola.com>
CC:	torvalds@...l.org, linux-kernel@...r.kernel.org,
	jaxboe@...ionio.com,
	OLUSANYA SOYANNWO <olusanya.soyannwo@...orola.com>,
	Hu Tao <taohu@...orola.com>
Subject: Re: [PATCH] scatterlist: prevent invalid free when alloc fails

Hello,

On 08/27/2010 09:45 PM, Jeffrey Carlyle wrote:
>>>               sg = alloc_fn(alloc_size, gfp_mask);
>>> -             if (unlikely(!sg))
>>> +             if (unlikely(!sg)) {
>>> +                     table->orig_nents = total_alloc;
>>> +                     /* mark the end of previous entry */
>>> +                     sg_mark_end(&prv[alloc_size - 1]);
>>
>> prv[alloc_size - 1] is already marked as end by sg_init_table() during
>> the previous iteration.  Also, prv can be NULL at this point.  AFAICS,
>> the only thing necessary would be "if (prv) table->nents++", no?
> 
> You are right about prv possibly being NULL here. Sorry for not
> catching that earlier; however, I don't think prv will be marked as an
> end in the previous iteration.

But we have sg_mark_end(&sgl[nents-1]) in sg_init_table().  I think
explicit end marking in __sg_alloc_table() is redundant.

Thanks.

-- 
tejun
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