Re: [PATCH] fuse: Apply flags2 only when userspace set the FUSE_INIT_EXT flag

[Vivek Goyal <vgoyal@redhat.com>]

On Thu, Apr 21, 2022 at 05:36:02PM +0200, Miklos Szeredi wrote:
> On Fri, 15 Apr 2022 at 13:54, Bernd Schubert <bschubert@ddn.com> wrote:
> >
> > This is just a safety precaution to avoid checking flags
> > on memory that was initialized on the user space side.
> > libfuse zeroes struct fuse_init_out outarg, but this is not
> > guranteed to be done in all implementations. Better is to
> > act on flags and to only apply flags2 when FUSE_INIT_EXT
> > is set.
> >
> > There is a risk with this change, though - it might break existing
> > user space libraries, which are already using flags2 without
> > setting FUSE_INIT_EXT.
> >
> > The corresponding libfuse patch is here
> > https://github.com/libfuse/libfuse/pull/662
> >
> >
> > Signed-off-by: Bernd Schubert <bschubert@ddn.com>
> 
> Agreed, this is a good change.  Applied.
> 
> Just one comment: please consider adding  "Fixes:" and "Cc:
> <stable@....>" tags next time.   I added them now.

I am afraid that this probably will break both C and rust version of
virtiofsd. I had a quick look and I can't seem to find these
implementations setting INIT_EXT flag in reply to init.

I am travelling. Will check it more closely when I return next week.
If virtiofsd implementations don't set INIT_EXT, I would rather prefer
to not do this change and avoid breaking it.

Thanks
Vivek