Re: [RESEND PATCH v2 v4.1-rc8 1/2] drm: prime: Honour O_RDWR during prime-handle-to-fd

[Daniel Vetter]

On Fri, Jun 19, 2015 at 02:52:28PM +0100, Daniel Thompson wrote:
> Currently DRM_IOCTL_PRIME_HANDLE_TO_FD rejects all flags except
> (DRM|O)_CLOEXEC making it difficult (maybe impossible) for userspace
> to mmap() the resulting dma-buf even when this is supported by the
> DRM driver.
> 
> It is trivial to relax the restriction and permit read/write access.
> This is safe because the flags are seldom touched by drm; mostly they
> are passed verbatim to dma_buf calls.
> 
> Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_prime.c | 9 +++------
>  include/uapi/drm/drm.h      | 1 +
>  2 files changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 7fec191b45f7..6d2cf4fb4038 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -331,7 +331,7 @@ static const struct dma_buf_ops drm_gem_prime_dmabuf_ops =  {
>   * drm_gem_prime_export - helper library implementation of the export callback
>   * @dev: drm_device to export from
>   * @obj: GEM object to export
> - * @flags: flags like DRM_CLOEXEC
> + * @flags: flags like DRM_CLOEXEC and DRM_RDWR
>   *
>   * This is the implementation of the gem_prime_export functions for GEM drivers
>   * using the PRIME helpers.
> @@ -639,14 +639,11 @@ int drm_prime_handle_to_fd_ioctl(struct drm_device *dev, void *data,
>  		return -ENOSYS;
>  
>  	/* check flags are valid */
> -	if (args->flags & ~DRM_CLOEXEC)
> +	if (args->flags & ~(DRM_CLOEXEC | DRM_RDWR))
>  		return -EINVAL;

I think we should reject DRM_RDWR if there's no mmap implementation in the
underlying dma-buf vfunc table. Or in the gem version of those. Otherwise
looks ok to me, if we first resolve the dma-buf userspace mmap coherency
issue.
-Daniel

>  
> -	/* we only want to pass DRM_CLOEXEC which is == O_CLOEXEC */
> -	flags = args->flags & DRM_CLOEXEC;
> -
>  	return dev->driver->prime_handle_to_fd(dev, file_priv,
> -			args->handle, flags, &args->fd);
> +			args->handle, args->flags, &args->fd);
>  }
>  
>  int drm_prime_fd_to_handle_ioctl(struct drm_device *dev, void *data,
> diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
> index ff6ef62d084b..092fe3fa8ec0 100644
> --- a/include/uapi/drm/drm.h
> +++ b/include/uapi/drm/drm.h
> @@ -668,6 +668,7 @@ struct drm_set_client_cap {
>  	__u64 value;
>  };
>  
> +#define DRM_RDWR O_RDWR
>  #define DRM_CLOEXEC O_CLOEXEC
>  struct drm_prime_handle {
>  	__u32 handle;
> -- 
> 2.4.3
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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