[Virtio-fs] [PATCH v3 5/6] fuse: Add a flag FUSE_OPEN_KILL_PRIV for open() request

[Miklos Szeredi]

On Fri, Nov 6, 2020 at 5:00 PM Vivek Goyal <vgoyal at redhat.com> wrote:
>
> On Fri, Nov 06, 2020 at 02:55:11PM +0100, Miklos Szeredi wrote:
> > On Fri, Oct 9, 2020 at 8:16 PM Vivek Goyal <vgoyal at redhat.com> wrote:
> > >
> > > With FUSE_HANDLE_KILLPRIV_V2 support, server will need to kill
> > > suid/sgid/security.capability on open(O_TRUNC), if server supports
> > > FUSE_ATOMIC_O_TRUNC.
> > >
> > > But server needs to kill suid/sgid only if caller does not have
> > > CAP_FSETID. Given server does not have this information, client
> > > needs to send this info to server.
> > >
> > > So add a flag FUSE_OPEN_KILL_PRIV to fuse_open_in request which tells
> > > server to kill suid/sgid(only if group execute is set).
> >
> > This is needed for FUSE_CREATE as well (which may act as a normal open
> > in case the file exists, and no O_EXCL was specified), right?
>
> Hi Miklos,
>
> IIUC, In current code we seem to use FUSE_CREATE only if file does not exist.
> If file exists, then we probably will take FUSE_OPEN path.

That's true if the cache is up to date, one important point for
FUSE_CREATE is that it works atomically even if the cache is stale.
So if cache is negative and we send a FUSE_CREATE it may still open an
*existing* file, and we want to do suid/caps clearing in that case
also, no?

Thanks,
Miklos