linux-ext4 - Re: [PATCH] ext4: Fix offset overflow on 32-bit archs in ext4_iomap

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Message-ID: <20180329133123.r33q776bmuqsiqcz@quack2.suse.cz>
Date:   Thu, 29 Mar 2018 15:31:23 +0200
From:   Jan Kara <jack@...e.cz>
To:     Eryu Guan <guaneryu@...il.com>
Cc:     Jan Kara <jack@...e.cz>, Ted Tso <tytso@....edu>,
        linux-ext4@...r.kernel.org, Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH] ext4: Fix offset overflow on 32-bit archs in
 ext4_iomap_begin()

On Fri 23-03-18 09:27:47, Eryu Guan wrote:
> On Tue, Feb 20, 2018 at 06:23:07PM +0100, Jan Kara wrote:
> > From: Jiri Slaby <jslaby@...e.cz>
> > 
> > ext4_iomap_begin() has a bug where offset returned in the iomap
> > structure will be truncated to unsigned long size. On 64-bit
> > architectures this is fine but on 32-bit architectures obviously not.
> > Not many places actually use the offset stored in the iomap structure
> > but one of visible failures is in SEEK_HOLE / SEEK_DATA implementation.
> > If we create a file like:
> > 
> > dd if=/dev/urandom of=file bs=1k seek=8m count=1
> > 
> > then
> > 
> > lseek64("file", 0x100000000ULL, SEEK_DATA)
> > 
> > wrongly returns 0x100000000 on unfixed kernel while it should return
> > 0x200000000. Avoid the overflow by proper type cast.
> 
> It looks like a good candidate for a regression test in fstests :)

Actually, one of SEEK_HOLE/SEEK_DATA tests in fstests will fail because of
this bug (I've checked that). Just not many people run fstests in fully
32-bit environments.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR