Patch "ext4: reinforce check of i_dtime when clearing high fields of uid and gid" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

ext4: reinforce check of i_dtime when clearing high fields of uid and gid

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ext4-reinforce-check-of-i_dtime-when-clearing-high-fields-of-uid-and-gid.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Daeho Jeong <[email protected]>
Date: Mon, 5 Sep 2016 22:56:10 -0400
Subject: ext4: reinforce check of i_dtime when clearing high fields of uid and gid

From: Daeho Jeong <[email protected]>

commit 93e3b4e6631d2a74a8cf7429138096862ff9f452 upstream.

Now, ext4_do_update_inode() clears high 16-bit fields of uid/gid of deleted and evicted inode to fix up interoperability with old kernels. However, it checks only i_dtime of an inode to determine whether the inode was deleted and evicted, and this is very risky, because i_dtime can be used for the pointer maintaining orphan inode list, too. We need to further check whether the i_dtime is being used for the orphan inode list even if the i_dtime is not NULL.

We found that high 16-bit fields of uid/gid of inode are unintentionally and permanently cleared when the inode truncation is just triggered, but not finished, and the inode metadata, whose high uid/gid bits are cleared, is written on disk, and the sudden power-off follows that in order.

---
 fs/ext4/inode.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

@@ -4549,14 +4549,14 @@ static int ext4_do_update_inode(handle_t
  * Fix up interoperability with old kernels. Otherwise, old inodes get
  * re-used with the upper 16 bits of the uid/gid intact
  */
-		if (!ei->i_dtime) {
+		if (ei->i_dtime && list_empty(&ei->i_orphan)) {
+			raw_inode->i_uid_high = 0;
+			raw_inode->i_gid_high = 0;
+		} else {
 			raw_inode->i_uid_high =
 				cpu_to_le16(high_16_bits(i_uid));
 			raw_inode->i_gid_high =
 				cpu_to_le16(high_16_bits(i_gid));
-		} else {
-			raw_inode->i_uid_high = 0;
-			raw_inode->i_gid_high = 0;
 		}
 	} else {
 		raw_inode->i_uid_low = cpu_to_le16(fs_high2lowuid(i_uid));

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/ext4-reinforce-check-of-i_dtime-when-clearing-high-fields-of-uid-and-gid.patch