linux-kernel - [PATCH 3.16 33/63] ext4: never move the system.data xattr out of the inode body

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Message-ID: <lsq.1537575342.695928015@decadent.org.uk>
Date:   Sat, 22 Sep 2018 01:15:42 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Theodore Ts'o" <tytso@....edu>
Subject: [PATCH 3.16 33/63] ext4: never move the system.data xattr out of
 the inode body

3.16.58-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Theodore Ts'o <tytso@....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@....edu>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/ext4/xattr.c | 5 +++++
 1 file changed, 5 insertions(+)

--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -1370,6 +1370,11 @@ 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);