linux-kernel - Re: [PATCH] fuse: Add ioctl flag for compat ioctl with 64-bit time

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Date:   Tue, 23 Apr 2019 14:55:19 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Ian Abbott <abbotti@....co.uk>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fuse: Add ioctl flag for compat ioctl with 64-bit time_t

On Fri, Mar 1, 2019 at 6:08 PM Ian Abbott <abbotti@....co.uk> 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.

Thanks,
Miklos

>
> Signed-off-by: Ian Abbott <abbotti@....co.uk>
> ---
>  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
>