linux-ext4 - ext4: buffer underrun in ext4_ext

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Message-ID: <4A7C7045.7040704@gmail.com>
Date:	Fri, 07 Aug 2009 20:19:49 +0200
From:	Roel Kluin <roel.kluin@...il.com>
To:	"Theodore Ts'o" <tytso@....edu>, linux-ext4@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: ext4: buffer underrun in ext4_ext_split()?

If `depth' is less or equal to `at', a buffer underrun occurs

Signed-off-by: Roel Kluin <roel.kluin@...il.com>
---
I am not sure whether this is possible.

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index afea652..25bc182 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -822,7 +822,7 @@ static int ext4_ext_split(handle_t *handle, struct inode *inode,
 	}
 
 	/* initialize new leaf */
-	newblock = ablocks[--a];
+	newblock = a ? ablocks[--a] : 0;
 	BUG_ON(newblock == 0);
 	bh = sb_getblk(inode->i_sb, newblock);
 	if (!bh) {
--
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