Re: [PATCH] fuse: Add ioctl flag for compat ioctl with 64-bit time_t

[Ian Abbott]

On 23/04/2019 13:55, Miklos Szeredi wrote:
> On Fri, Mar 1, 2019 at 6:08 PM Ian Abbott <abbotti@xxxxxxxxx> wrote:
> > Currently, a CUSE server running on a 64-bit kernel can tell when an
> > ioctl request comes from a process running a 32-bit ABI, but cannot tell
> > whether the requesting process is using legacy IA32 emulation or x32
> > ABI, for example.  In particular, the server does not know the size of
> > the client process's `time_t` type.
> >
> > For 64-bit kernels, the `FUSE_IOCTL_COMPAT` and `FUSE_IOCTL_32BIT` flags
> > are currently set in the ioctl input request (`struct fuse_ioctl_in`
> > member `flags`) for a 32-bit requesting process.  This patch defines a
> > new flag `FUSE_IOCTL_COMPAT_64TIME` and sets it if the 32-bit requesting
> > process (running on a 64-bit kernel) uses a 64-bit `time_t` type.
>
> Hi,
>
> Thanks for the patch.
>
> I think it should rather use in_x32_syscall() helper and follow that
> naming because there's apparently at least one example in xfs of a
> non-time_t related ioctl that varies between the x32 vs ia32.

Hi Miklos,

It is conceivable that COMPAT_USE_64BIT_TIME could be true for some 
other arch/ABI (although currently it is only ever set for x86/x32). 
Should it have separate flags for "compat 64-bit time" and "compat x32" 
(even though that is currently redundant)?

Kind regards,
Ian.

> Thanks,
> Miklos
>
> > Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
> > ---
> >   fs/fuse/file.c            | 5 ++++-
> >   include/uapi/linux/fuse.h | 2 ++
> >   2 files changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> > index 06096b60f1df..9777e7a19889 100644
> > --- a/fs/fuse/file.c
> > +++ b/fs/fuse/file.c
> > @@ -2576,8 +2576,11 @@ long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
> >   #if BITS_PER_LONG == 32
> >          inarg.flags |= FUSE_IOCTL_32BIT;
> >   #else
> > -       if (flags & FUSE_IOCTL_COMPAT)
> > +       if (flags & FUSE_IOCTL_COMPAT) {
> >                  inarg.flags |= FUSE_IOCTL_32BIT;
> > +               if (COMPAT_USE_64BIT_TIME)
> > +                       inarg.flags |= FUSE_IOCTL_COMPAT_64TIME;
> > +       }
> >   #endif
> >
> >          /* assume all the iovs returned by client always fits in a page */
> > diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> > index 2ac598614a8f..1f4a71486601 100644
> > --- a/include/uapi/linux/fuse.h
> > +++ b/include/uapi/linux/fuse.h
> > @@ -335,6 +335,7 @@ struct fuse_file_lock {
> >    * FUSE_IOCTL_RETRY: retry with new iovecs
> >    * FUSE_IOCTL_32BIT: 32bit ioctl
> >    * FUSE_IOCTL_DIR: is a directory
> > + * FUSE_IOCTL_COMPAT_64TIME: 32bit compat ioctl with 64bit time_t
> >    *
> >    * FUSE_IOCTL_MAX_IOV: maximum of in_iovecs + out_iovecs
> >    */
> > @@ -343,6 +344,7 @@ struct fuse_file_lock {
> >   #define FUSE_IOCTL_RETRY       (1 << 2)
> >   #define FUSE_IOCTL_32BIT       (1 << 3)
> >   #define FUSE_IOCTL_DIR         (1 << 4)
> > +#define FUSE_IOCTL_COMPAT_64TIME (1 << 5)
> >
> >   #define FUSE_IOCTL_MAX_IOV     256
> >
> > --
> > 2.20.1


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