[PATCH] drm/vmwgfx: validate pitch coming from userspace

Validate the pitch, alongside the box dimensions before trying
to copy data from the underlying surface. Fixes possible
out of bounds reads with cursor snooping.

Fixes: 2ac863719e51 ("vmwgfx: Snoop DMA transfers with non-covering sizes")
Cc: [email protected]
Reported-by: Youness HFA <[email protected]>
Signed-off-by: Zack Rusin <[email protected]>
---
 drivers/gpu/drm/vmwgfx/vmwgfx_cursor_plane.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_cursor_plane.c b/drivers/gpu/drm/vmwgfx/vmwgfx_cursor_plane.c
index d1e7df500190..f4d14b00d7aa 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_cursor_plane.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_cursor_plane.c
@@ -324,6 +324,7 @@ void vmw_kms_cursor_snoop(struct vmw_surface *srf,
 	unsigned long kmap_num;
 	SVGA3dCopyBox *box;
 	u32 box_count;
+	u64 src_extent;
 	void *virtual;
 	bool is_iomem;
 	struct vmw_dma_cmd {
@@ -372,8 +373,19 @@ void vmw_kms_cursor_snoop(struct vmw_surface *srf,
 		return;
 	}
 
+	if (box->w == 0 || box->h == 0)
+		return;
+
+	src_extent = (u64)(box->h - 1) * cmd->dma.guest.pitch +
+		     (u64)box->w * desc->pitchBytesPerBlock;
+	if (src_extent > bo->base.size) {
+		DRM_ERROR("Cursor snoop source of %llu bytes exceeds the %zu byte buffer\n",
+			  src_extent, bo->base.size);
+		return;
+	}
+
 	kmap_offset = cmd->dma.guest.ptr.offset >> PAGE_SHIFT;
-	kmap_num = (VMW_CURSOR_SNOOP_HEIGHT * image_pitch) >> PAGE_SHIFT;
+	kmap_num = PFN_UP(src_extent);
 
 	ret = ttm_bo_reserve(bo, true, false, NULL);
 	if (unlikely(ret != 0)) {
@@ -387,14 +399,16 @@ void vmw_kms_cursor_snoop(struct vmw_surface *srf,
 
 	virtual = ttm_kmap_obj_virtual(&map, &is_iomem);
 
-	if (box->w == VMW_CURSOR_SNOOP_WIDTH && cmd->dma.guest.pitch == image_pitch) {
+	if (box->w == VMW_CURSOR_SNOOP_WIDTH &&
+	    box->h == VMW_CURSOR_SNOOP_HEIGHT &&
+	    cmd->dma.guest.pitch == image_pitch) {
 		memcpy(srf->snooper.image, virtual,
 		       VMW_CURSOR_SNOOP_HEIGHT * image_pitch);
 	} else {
 		/* Image is unsigned pointer. */
 		for (i = 0; i < box->h; i++)
 			memcpy(srf->snooper.image + i * image_pitch,
-			       virtual + i * cmd->dma.guest.pitch,
+			       virtual + (size_t)i * cmd->dma.guest.pitch,
 			       box->w * desc->pitchBytesPerBlock);
 	}
 	srf->snooper.id++;
-- 
2.53.0