[PATCH 3.2 018/126] ext4: reinforce check of i_dtime when clearing high fields of uid and gid

From: Ben Hutchings
Date: Wed Feb 15 2017 - 18:08:32 EST

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


From: Daeho Jeong <daeho.jeong@xxxxxxxxxxx>

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.

Signed-off-by: Daeho Jeong <daeho.jeong@xxxxxxxxxxx>
Signed-off-by: Hobin Woo <hobin.woo@xxxxxxxxxxx>
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
fs/ext4/inode.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4093,14 +4093,14 @@ 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 =
raw_inode->i_gid_high =
- } else {
- raw_inode->i_uid_high = 0;
- raw_inode->i_gid_high = 0;
} else {
raw_inode->i_uid_low =