linux-ext4 - [RFC] ext4_bmap() may return blocks outside filesystem

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Message-ID: <498AD58B.5000805@ph.tum.de>
Date:	Thu, 05 Feb 2009 13:03:23 +0100
From:	Thiemo Nagel <thiemo.nagel@...tum.de>
To:	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Theodore Tso <tytso@....edu>
Subject: [RFC] ext4_bmap() may return blocks outside filesystem

Hello,

during testing of ext4 with intentionally corrupted filesystem images I 
noticed that sometimes ext4_bmap() returns physical block numbers which 
lie outside of the filesystem.  In most cases, the error is caught by 
the block layer (?) leading to error messages of the kind:

attempt to access beyond end of device
loop0: rw=0, want=xxx, limit=xxx

But there also are cases which are not handled gracefully by bmap() callers.

I've attached a conceptual patch against 2.6.29-rc2 which fixes one case 
in which invalid block numbers are returned (there might be more) by 
adding sanity checks to ext4_ext_find_extent(), but before I start 
looking for further occurences, I'd like to ask whether you think my 
approach is reasonable.

Kind regards,

Thiemo Nagel

View attachment "concept.patch" of type "text/x-patch" (789 bytes)