[PATCH v4.4.y] ext4: never move the system.data xattr out of the inode body

[PATCH v4.4.y] ext4: never move the system.data xattr out of the inode body

[Zubin Mithra]

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

Backport Note:
- dfa2064b22("ext4: factor out loop for freeing inode xattr space")
factored out the loop from inside ext4_expand_extra_isize_ea to a
separate function named ext4_xattr_make_inode_space. As the above commit
is not present in 4.4.y, make the change inside ext4_expand_extra_isize_ea.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
Signed-off-by: Zubin Mithra <zsm@chromium.org>
---
 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);
-- 
2.19.0.605.g01d371f741-goog

Re: [PATCH v4.4.y] ext4: never move the system.data xattr out of the inode body

[Greg KH]

On Fri, Sep 28, 2018 at 09:21:44AM -0700, Zubin Mithra 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
> 
> Backport Note:
> - dfa2064b22("ext4: factor out loop for freeing inode xattr space")
> factored out the loop from inside ext4_expand_extra_isize_ea to a
> separate function named ext4_xattr_make_inode_space. As the above commit
> is not present in 4.4.y, make the change inside ext4_expand_extra_isize_ea.


What about a 4.9.y version of this?  I can't just take a 4.4 version
because someone would suffer a regression if they moved from 4.4.y to
4.9.y :(

thanks,

greg k-h