drm: prime: Honour O_RDWR during prime-handle-to-fd

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.

v3 (Tiago): removed unused flags variable from drm_prime_handle_to_fd_ioctl.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Tiago Vignatti <tiago.vignatti@intel.com>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1450820214-12509-2-git-send-email-tiago.vignatti@intel.com

2 files changed, 4 insertions, 7 deletions

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 27aa7183b20b..df6cdc76a16e 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -329,7 +329,7 @@ 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.
@@ -628,7 +628,6 @@ int drm_prime_handle_to_fd_ioctl(struct drm_device *dev, void *data,
                                  struct drm_file *file_priv)
 {
         struct drm_prime_handle *args = data;
-        uint32_t flags;
 
         if (!drm_core_check_feature(dev, DRIVER_PRIME))
                 return -EINVAL;
@@ -637,14 +636,11 @@ 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;
 
-        /* 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 b4e92eb12044..a0ebfe7c9a28 100644
--- a/include/uapi/drm/drm.h
+++ b/include/uapi/drm/drm.h
@@ -669,6 +669,7 @@ struct drm_set_client_cap {
         __u64 value;
 };
 
+#define DRM_RDWR O_RDWR
 #define DRM_CLOEXEC O_CLOEXEC
 struct drm_prime_handle {
         __u32 handle;