linux-ext4 - [patch 077/277] ext3: validate directory entry data before use

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Message-Id: <200807250846.m6P8kV4b001159@imap1.linux-foundation.org>
Date:	Fri, 25 Jul 2008 01:46:31 -0700
From:	akpm@...ux-foundation.org
To:	torvalds@...ux-foundation.org
Cc:	akpm@...ux-foundation.org, duaneg@...da.com,
	linux-ext4@...r.kernel.org
Subject: [patch 077/277] ext3: validate directory entry data before use

From: "Duane Griffin" <duaneg@...da.com>

ext3_dx_find_entry uses ext3_next_entry without verifying that the entry
is valid.  If its rec_len == 0 this causes an infinite loop.  Refactor the
loop to check the validity of entries before checking whether they match
and moving onto the next one.

There are other uses of ext3_next_entry in this file which also look
problematic.  They should be reviewed and fixed if/when we have a
test-case that triggers them.

This patch fixes the first case (image hdb.25.softlockup.gz) reported in
http://bugzilla.kernel.org/show_bug.cgi?id=10882.

Signed-off-by: Duane Griffin <duaneg@...da.com>
Cc: <linux-ext4@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 fs/ext3/namei.c |   22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff -puN fs/ext3/namei.c~ext3-validate-directory-entry-data-before-use-v5 fs/ext3/namei.c
--- a/fs/ext3/namei.c~ext3-validate-directory-entry-data-before-use-v5
+++ a/fs/ext3/namei.c
@@ -991,19 +991,21 @@ static struct buffer_head * ext3_dx_find
 		de = (struct ext3_dir_entry_2 *) bh->b_data;
 		top = (struct ext3_dir_entry_2 *) ((char *) de + sb->s_blocksize -
 				       EXT3_DIR_REC_LEN(0));
-		for (; de < top; de = ext3_next_entry(de))
-		if (ext3_match (namelen, name, de)) {
-			if (!ext3_check_dir_entry("ext3_find_entry",
-						  dir, de, bh,
-				  (block<<EXT3_BLOCK_SIZE_BITS(sb))
-					  +((char *)de - bh->b_data))) {
-				brelse (bh);
+		for (; de < top; de = ext3_next_entry(de)) {
+			int off = (block << EXT3_BLOCK_SIZE_BITS(sb))
+				  + ((char *) de - bh->b_data);
+
+			if (!ext3_check_dir_entry(__func__, dir, de, bh, off)) {
+				brelse(bh);
 				*err = ERR_BAD_DX_DIR;
 				goto errout;
 			}
-			*res_dir = de;
-			dx_release (frames);
-			return bh;
+
+			if (ext3_match(namelen, name, de)) {
+				*res_dir = de;
+				dx_release(frames);
+				return bh;
+			}
 		}
 		brelse (bh);
 		/* Check to see if we should continue to search */
_
--
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