linux-kernel - Re: [PATCH 1/1] nilfs2: fix potential memory overrun on inode

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Date:	Sat, 21 Feb 2015 09:22:08 +0900 (JST)
From:	Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-nilfs@...r.kernel.org
Subject: Re: [PATCH 1/1] nilfs2: fix potential memory overrun on inode

On Fri, 20 Feb 2015 13:58:42 -0800, Andrew Morton wrote:
> On Fri, 20 Feb 2015 22:46:35 +0900 Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp> wrote:
> 
>> Each inode of nilfs2 stores a root node of a b-tree, and it turned out
>> to have a memory overrun issue:
>> 
>> Each b-tree node of nilfs2 stores a set of key-value pairs and the
>> number of them (in "bn_nchildren" member of nilfs_btree_node struct),
>> as well as a few other "bn_*" members.
>> 
>> Since the value of "bn_nchildren" is used for operations on the
>> key-values within the b-tree node, it can cause memory access overrun
>> if a large number is incorrectly set to "bn_nchildren".
>> 
>> For instance, nilfs_btree_node_lookup() function determines the range
>> of binary search with it, and too large "bn_nchildren" leads
>> nilfs_btree_node_get_key() in that function to overrun.
>> 
>> As for intermediate b-tree nodes, this is prevented by a sanity check
>> performed when each node is read from a drive, however, no sanity
>> check has been done for root nodes stored in inodes.
>> 
>> This patch fixes the issue by adding missing sanity check against
>> b-tree root nodes so that it's called when on-memory inodes are read
>> from ifile, inode metadata file.
> 
> How would one trigger this overrun?  Mount an fs with a deliberately
> corrupted/inconsistent fs image?

Yes, this can be triggered by mounting an fs with a corrupted image
deliberately or by chance.

> Memory overrun sounds nasty so I'm thinking we add cc:stable to this
> one.  OK?

Agreed.

Ryusuke Konishi
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