linux-kernel - Re: Endless getdents() in vfat filesystem

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Message-ID: <56472C2F.5090207@oracle.com>
Date:	Sat, 14 Nov 2015 13:42:23 +0100
From:	Vegard Nossum <vegard.nossum@...cle.com>
To:	Richard Weinberger <richard.weinberger@...il.com>
Cc:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Endless getdents() in vfat filesystem

On 11/14/2015 11:32 AM, Richard Weinberger wrote:
> On Sat, Nov 14, 2015 at 2:19 AM, Vegard Nossum <vegard.nossum@...cle.com> wrote:
>> Hi,
>>
>> Using the attached disk image I observe that getdents() never returns
>> the end of the directory, i.e. mounting the disk image on a loopback
>> device and running 'ls' under strace shows an endless stream of:
>>
>> getdents(3, /* 2 entries */, 32768)     = 48
>> getdents(3, /* 2 entries */, 32768)     = 48
>> getdents(3, /* 2 entries */, 32768)     = 48
>> ...
>
> Please more details. Is this image hand crafted?
> If not, how has it been created? Is is supposed to work?

It was created by fuzzing, it is not supposed to work per se.

>  From a quick look it seems as the root directory is bad but we report
> progress in ->iterate.
> ctx->pos is 2, we set it back to 0, because of the faked dot entries.
> but fat_get_entry() did not make any progress and we report 0 back to VFS.
> So, VFS sees progress and the game continues.
>
> Does the attached patch help?

Yes, it does fixes the problem here, but I can't really comment on the
correctness of the patch.

Thanks for the quick reponse,


Vegard
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