linux-kernel - Re: [PATCH 00/10] AXFS: Advanced XIP filesystem

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Date:	Fri, 22 Aug 2008 17:19:06 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
Cc:	Jared Hulbert <jaredeh@...il.com>, Linux-kernel@...r.kernel.org,
	linux-embedded@...r.kernel.org,
	linux-mtd <linux-mtd@...ts.infradead.org>,
	Jörn Engel <joern@...fs.org>,
	tim.bird@...sony.com, cotte@...ibm.com, nickpiggin@...oo.com.au
Subject: Re: [PATCH 00/10] AXFS: Advanced XIP filesystem

On Friday 22 August 2008, Geert Uytterhoeven wrote:
> I gave AxFS a try on PS3 (ppc64, always use big-endian 64-bit for testing new
> code ;-).
> When mounting the image, I got the crash below:
> 
> | attempt to access beyond end of device
> | loop0: rw=0, want=4920, limit=4912
> | Unable to handle kernel paging request for data at address 0x00000028


Offset 0x28 is buffer_head->b_data, so it seems like sb_bread returns NULL,
which it does for out of range block numbers. I guess axfs_copy_block
should check for that condition, as it can happen on malicious file system
images.
I agree that this is likely to get caused by an endianess bug.
A good help for finding endianess bugs is to use __be64 like data types
everywhere and test with sparse -D__CHECK_ENDIAN__.

	Arnd 
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