[3.8.y.z extended stable] Patch "ext4: check for overlapping extents in ext4_valid_extent_entries()" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    ext4: check for overlapping extents in ext4_valid_extent_entries()

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.16.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 973ab5447fd3742c15014df74616124812efb72c Mon Sep 17 00:00:00 2001
From: Eryu Guan <guaneryu at gmail.com>
Date: Tue, 3 Dec 2013 21:22:21 -0500
Subject: ext4: check for overlapping extents in ext4_valid_extent_entries()
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

commit 5946d089379a35dda0e531710b48fca05446a196 upstream.

A corrupted ext4 may have out of order leaf extents, i.e.

extent: lblk 0--1023, len 1024, pblk 9217, flags: LEAF UNINIT
extent: lblk 1000--2047, len 1024, pblk 10241, flags: LEAF UNINIT
             ^^^^ overlap with previous extent

Reading such extent could hit BUG_ON() in ext4_es_cache_extent().

	BUG_ON(end < lblk);

The problem is that __read_extent_tree_block() tries to cache holes as
well but assumes 'lblk' is greater than 'prev' and passes underflowed
length to ext4_es_cache_extent(). Fix it by checking for overlapping
extents in ext4_valid_extent_entries().

I hit this when fuzz testing ext4, and am able to reproduce it by
modifying the on-disk extent by hand.

Also add the check for (ee_block + len - 1) in ext4_valid_extent() to
make sure the value is not overflow.

Ran xfstests on patched ext4 and no regression.

Cc: Lukáš Czerner <lczerner at redhat.com>
Signed-off-by: Eryu Guan <guaneryu at gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso at mit.edu>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/ext4/extents.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index c3db941..8b5c264 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -363,8 +363,10 @@ static int ext4_valid_extent(struct inode *inode, struct ext4_extent *ext)
 {
 	ext4_fsblk_t block = ext4_ext_pblock(ext);
 	int len = ext4_ext_get_actual_len(ext);
+	ext4_lblk_t lblock = le32_to_cpu(ext->ee_block);
+	ext4_lblk_t last = lblock + len - 1;

-	if (len == 0)
+	if (lblock > last)
 		return 0;
 	return ext4_data_block_valid(EXT4_SB(inode->i_sb), block, len);
 }
@@ -390,11 +392,26 @@ static int ext4_valid_extent_entries(struct inode *inode,
 	if (depth == 0) {
 		/* leaf entries */
 		struct ext4_extent *ext = EXT_FIRST_EXTENT(eh);
+		struct ext4_super_block *es = EXT4_SB(inode->i_sb)->s_es;
+		ext4_fsblk_t pblock = 0;
+		ext4_lblk_t lblock = 0;
+		ext4_lblk_t prev = 0;
+		int len = 0;
 		while (entries) {
 			if (!ext4_valid_extent(inode, ext))
 				return 0;
+
+			/* Check for overlapping extents */
+			lblock = le32_to_cpu(ext->ee_block);
+			len = ext4_ext_get_actual_len(ext);
+			if ((lblock <= prev) && prev) {
+				pblock = ext4_ext_pblock(ext);
+				es->s_last_error_block = cpu_to_le64(pblock);
+				return 0;
+			}
 			ext++;
 			entries--;
+			prev = lblock + len - 1;
 		}
 	} else {
 		struct ext4_extent_idx *ext_idx = EXT_FIRST_INDEX(eh);
--
1.8.3.2