linux-ext4 - Re: [PATCH] Fix oops in mballoc caused by a variable overflow

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Date:	Thu, 17 Jan 2008 14:09:41 +0100
From:	Valerie Clement <valerie.clement@...l.net>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	Mingming Cao <cmm@...ibm.com>,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] Fix oops in mballoc caused by a variable overflow

Aneesh Kumar K.V wrote:
> On Thu, Jan 17, 2008 at 10:43:40AM +0100, Valerie Clement wrote:
>> Aneesh Kumar K.V wrote:
>>> What about this  ? I guess we will overflow start = start << bsbits;
>>>
>> Hi Aneesh,
>> your patch below doesn't fix the issue, because as start_off is also  
>> loff_t, start_off = ac->ac_o_ex.fe_logical << bsbits  also overflows.
>>
> 
> loff_t is 64 bits.
> 
> typedef __kernel_loff_t         loff_t;
> typedef long long       __kernel_loff_t;
> typedef __u32 ext4_lblk_t;
> typedef unsigned long long ext4_fsblk_t
> 
> start_off = ac->ac_o_ex.fe_logical << bsbits;
> 
> In the above line what we are storing in start_off is the offset in bytes.So it makes
> sense to use the type loff_t. It is neither logical block nor physical block.

Oh yes, sorry, you're right. I read too quickly.

In fact, it's missing a cast :
   start_off = (loff_t) ac->ac_o_ex.fe_logical << bsbits;

With that change, the test is ok.

    Valérie


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