[PATCH] drm: integer overflow in drm_mode_dirtyfb_ioctl()

[Xi Wang]

There is a potential integer overflow in drm_mode_dirtyfb_ioctl()
if userspace passes in a large num_clips.  The call to kmalloc would
allocate a small buffer, and the call to fb->funcs->dirty may result
in a memory corruption.

Reported-by: Haogang Chen <haogangchen@xxxxxxxxx>
Signed-off-by: Xi Wang <xi.wang@xxxxxxxxx>
Cc: stable@xxxxxxxxxx
Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx>

(cherry-picked from commit a5cd335165e31db9dbab636fd29895d41da55dd2 upstream)
Signed-off-by: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/drm_crtc.c |    4 ++++
 include/drm/drm_mode.h     |    2 ++
 2 files changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 405c63b..8323fc3 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -1873,6 +1873,10 @@ int drm_mode_dirtyfb_ioctl(struct drm_device *dev,
 	}

 	if (num_clips && clips_ptr) {
+		if (num_clips < 0 || num_clips > DRM_MODE_FB_DIRTY_MAX_CLIPS) {
+			ret = -EINVAL;
+			goto out_err1;
+		}
 		clips = kzalloc(num_clips * sizeof(*clips), GFP_KERNEL);
 		if (!clips) {
 			ret = -ENOMEM;
diff --git a/include/drm/drm_mode.h b/include/drm/drm_mode.h
index d30bedf..ddd46db 100644
--- a/include/drm/drm_mode.h
+++ b/include/drm/drm_mode.h
@@ -235,6 +235,8 @@ struct drm_mode_fb_cmd {
 #define DRM_MODE_FB_DIRTY_ANNOTATE_FILL 0x02
 #define DRM_MODE_FB_DIRTY_FLAGS         0x03

+#define DRM_MODE_FB_DIRTY_MAX_CLIPS     256
+
 /*
  * Mark a region of a framebuffer as dirty.
  *
--
1.7.9.5

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