Transmute flag is not inheritted on overlay fs

[Mengchi Cheng <mengcc@amazon.com>]

Hello,

On the overlay ext4 file system, we found that transmute flag is not
inherited by newly created sub-directories. The issue can be recreated on
the newest kernel(6.3.0-rc6) on qemux86-64 with following steps.

/data directory is mounted on /dev/vdb which is a ext4 fs. It is remounted
as an overlay again to upperdir /home/root/data.
# mount -t overlay overlay -o lowerdir=/data,upperdir=/home/root/data,workdir=/home/root/data_work /data
Add a new smack rule and set label and flag to /data directory.
# echo "_ system rwxatl" > /sys/fs/smackfs/load2
# chsmack -a "system" /data
# chsmack -t /data
Create directories under /data.
# mkdir -p /data/dir1/dir2
And then check the smack label of dir1 and dir2.
# chsmack /data/dir1
/data/dir1 access="system"
# chsmack /data/dir1/dir2
/data/dir1/dir2 access="_"
We can see dir1 did not inherit transmute flag from data and dir2 got the
process label.

The transmute xattr of the inode is set inside the smack_d_instantiate
which depends on SMK_INODE_CHANGED bit of isp->smk_flags. But the bit is
not set in the overlay fs mkdir function call chain. So one simple solution
we have is passing inode ptr into smack_dentry_create_files_as and set the
SMK_INODE_CHANGED bit if parent dir is transmuting. Although it looks
reasonable to me and we did not meet any issue in testing, I am not sure if
there is a better solution to it. It will be great, if experts could take
a look.


Thanks,
Mengchi Cheng