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

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Date:	Thu, 17 Jan 2008 21:59:28 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Valerie Clement <valerie.clement@...l.net>
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

On Thu, Jan 17, 2008 at 02:09:41PM +0100, Valerie Clement wrote:
> 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.

Updated patch below.

-aneesh

View attachment "overflow-fix.patch" of type "text/x-diff" (2740 bytes)