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

[Daniel Thompson]

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 at linaro.org>
---
 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;
 
-	/* 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