Re: [PATCH v2 1/1] common/encrypt: Do not run _verify_ciphertext_for_encryption_policy on compressed FS

[Eric Biggers <ebiggers@kernel.org>]

On Tue, Sep 16, 2025 at 02:13:39PM +0200, Jan Prusakowski wrote:
> On Mon, Sep 15, 2025 at 4:40 PM Eric Biggers <ebiggers@kernel.org> wrote:
> >
> > On Mon, Sep 15, 2025 at 12:04:51PM +0200, Jan Prusakowski wrote:
> > > common/encrypt: Do not run _verify_ciphertext_for_encryption_policy on compressed FS
> >
> > A better title would be something like
> > "common/encrypt: Explicitly set the test file to uncompressed".
> 
> Agreed, will fix that in v3.
> 
> > > @@ -790,6 +790,13 @@ _do_verify_ciphertext_for_encryption_policy()
> > >       _set_encpolicy $dir $keyspec $set_encpolicy_args -f $policy_flags
> > >       for src in $tmp.testfile_*; do
> > >               dst=$dir/${src##*.}
> > > +             # To make sure the test file is not compressed we create an empty one
> > > +             # and disable compression first (F2FS won't allow resetting the
> > > +             # compression flag if the file has data already in it).
> > > +             touch $dst
> > > +             if lsattr $dst | grep -qE ".+c.+ $dst" ; then
> > > +                     chattr -c $dst
> > > +             fi
> > >               cp $src $dst
> > >               inode=$(stat -c %i $dst)
> > >               blocklist=$(_get_ciphertext_block_list $dst)
> >
> > Is adding 'm' (FS_NOCOMP_FL) needed too?  If not, why does it exist?
> 
> In my setup files created have FS_COMPR_FL set from the start. Just clearing
> FS_COMPR_FL appears to help as now all the tests using
> _verify_ciphertext_for_encryption_policy
> pass when I run them on f2fs with "-o compress_extension=*".
> 
> Do you think we should add 'm' (FS_NOCOMP_FL) as well just in case some other FS
> behaves differently? Do you have any ideas on what other FS I should check?

I think so.  It doesn't look like f2fs does anything with FS_NOCOMP_FL,
other than enforce that it's mutually exclusive with FS_COMPR_FL.  But
there could be filesystems where 0 gives the default behavior (which
could be compress) and FS_NOCOMP_FL is needed to disable compression.

btrfs might do that, actually.  It doesn't support encryption yet,
though, so these tests can't be run on btrfs.

I would just add FS_NOCOMP_FL and make sure it still works on f2fs.

- Eric