Transmute flag is not inheritted on overlay fs

[Casey Schaufler]

On 4/18/2023 5:23 PM, Mengchi Cheng wrote:
> 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.

I will be happy to look at your solution. Please post a patch.

>
>
> Thanks,
> Mengchi Cheng
>