drm: fd.o Bug #7595: Avoid u32 overflows in radeon_check_and_fixup_offset().

The overflows could cause valid offsets to get rejected under some
circumstances, e.g. when the framebuffer resides at the very end of the card's
address space.
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/char/drm/radeon_state.c

@@ -42,7 +42,11 @@ static __inline__ int radeon_check_and_fixup_offset(drm_radeon_private_t *
 						    drm_file_t * filp_priv,
 						    u32 *offset)
 {
-	u32 off = *offset;
+	u64 off = *offset;
+	u32 fb_start = dev_priv->fb_location;
+	u32 fb_end = fb_start + dev_priv->fb_size - 1;
+	u32 gart_start = dev_priv->gart_vm_start;
+	u32 gart_end = gart_start + dev_priv->gart_size - 1;
 	struct drm_radeon_driver_file_fields *radeon_priv;
 
 	/* Hrm ... the story of the offset ... So this function converts
@@ -62,10 +66,8 @@ static __inline__ int radeon_check_and_fixup_offset(drm_radeon_private_t *
 	/* First, the best case, the offset already lands in either the
 	 * framebuffer or the GART mapped space
 	 */
-	if ((off >= dev_priv->fb_location &&
-	     off < (dev_priv->fb_location + dev_priv->fb_size)) ||
-	    (off >= dev_priv->gart_vm_start &&
-	     off < (dev_priv->gart_vm_start + dev_priv->gart_size)))
+	if ((off >= fb_start && off <= fb_end) ||
+	    (off >= gart_start && off <= gart_end))
 		return 0;
 
 	/* Ok, that didn't happen... now check if we have a zero based
@@ -78,16 +80,13 @@ static __inline__ int radeon_check_and_fixup_offset(drm_radeon_private_t *
 	}
 
 	/* Finally, assume we aimed at a GART offset if beyond the fb */
-	if (off > (dev_priv->fb_location + dev_priv->fb_size))
-		off = off - (dev_priv->fb_location + dev_priv->fb_size) +
-			dev_priv->gart_vm_start;
+	if (off > fb_end)
+		off = off - fb_end - 1 + gart_start;
 
 	/* Now recheck and fail if out of bounds */
-	if ((off >= dev_priv->fb_location &&
-	     off < (dev_priv->fb_location + dev_priv->fb_size)) ||
-	    (off >= dev_priv->gart_vm_start &&
-	     off < (dev_priv->gart_vm_start + dev_priv->gart_size))) {
-		DRM_DEBUG("offset fixed up to 0x%x\n", off);
+	if ((off >= fb_start && off <= fb_end) ||
+	    (off >= gart_start && off <= gart_end)) {
+		DRM_DEBUG("offset fixed up to 0x%x\n", (unsigned int)off);
 		*offset = off;
 		return 0;
 	}