Re: [PATCH v4.9.y] ext4: never move the system.data xattr out of the inode body

["SZ Lin (林上智)" <sz.lin@moxa.com>]

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Hi,

On Sun, Sep 30, 2018 at 10:17:48AM -0700, Guenter Roeck wrote:
> From: Theodore Ts'o <tytso@mit.edu>
> 
> commit 8cdb5240ec5928b20490a2bb34cb87e9a5f40226 upstream.
> 
> When expanding the extra isize space, we must never move the
> system.data xattr out of the inode body.  For performance reasons, it
> doesn't make any sense, and the inline data implementation assumes
> that system.data xattr is never in the external xattr block.
> 
> This addresses CVE-2018-10880
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=200005
> 
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
> Cc: stable@kernel.org
> [groeck: Context changes]
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
> I thought the 4.4.y backport should apply, but I think it doesn't after
> all. This backport applies to v4.9.y.

This patch got a conflict in 4.4.y stable kernel, I've tweaked the context
for 4.4.y backporting.

Attached is the 4.4.y backport patch which was compiled successfully with
following environment setting.

kernel version: v4.4.159
toolchain: GCC 8.2.0
config: x86_64_defconfig

--
SZ Lin (林上智)

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>From 2793f91d47ba4fd0e45f532ff7345d9ed459f083 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@mit.edu>
Date: Sat, 16 Jun 2018 15:40:48 -0400
Subject: [PATCH] ext4: never move the system.data xattr out of the inode body

commit 8cdb5240ec5928b20490a2bb34cb87e9a5f40226 upstream

When expanding the extra isize space, we must never move the
system.data xattr out of the inode body.  For performance reasons, it
doesn't make any sense, and the inline data implementation assumes
that system.data xattr is never in the external xattr block.

This addresses CVE-2018-10880

https://bugzilla.kernel.org/show_bug.cgi?id=200005

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
[SZ Lin (林上智): Tweak context for 4.4.y backporting]
Signed-off-by: SZ Lin (林上智) <sz.lin@moxa.com>
---
 fs/ext4/xattr.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 9fb2a751fce4..b51bb73b06a6 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -1386,6 +1386,11 @@ retry:
 		/* Find the entry best suited to be pushed into EA block */
 		entry = NULL;
 		for (; !IS_LAST_ENTRY(last); last = EXT4_XATTR_NEXT(last)) {
+			/* never move system.data out of the inode */
+			if ((last->e_name_len == 4) &&
+			    (last->e_name_index == EXT4_XATTR_INDEX_SYSTEM) &&
+			    !memcmp(last->e_name, "data", 4))
+				continue;
 			total_size =
 			EXT4_XATTR_SIZE(le32_to_cpu(last->e_value_size)) +
 					EXT4_XATTR_LEN(last->e_name_len);
-- 
2.19.0