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>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index bb4faf2d0c5cc902477d424ace5df15a5bc3a843..5f67ef828ccd7830e8e7663b7886874547601877 100644 (file)
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -1391,6 +1391,11 @@ 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);