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

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Date:	Thu, 17 Jan 2008 12:07:16 -0800
From:	Mingming Cao <cmm@...ibm.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	Valerie Clement <valerie.clement@...l.net>,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] Fix oops in mballoc caused by a variable overflow

On Thu, 2008-01-17 at 21:59 +0530, Aneesh Kumar K.V wrote:
> 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.
> 
Thanks, folded to the mballoc-core patch

Mingming
> -aneesh

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