render: Fix out of boundary heap access

ProcRenderCreateRadialGradient and ProcRenderCreateConicalGradient must
be protected against an integer overflow during length check. This is
already included in ProcRenderCreateLinearGradient since the fix for
CVE-2008-2362.

This can only be successfully exploited on a 32 bit system for an
out of boundary read later on. Validated by using ASAN.

Reviewed-by: Adam Jackson <ajax@redhat.com>

render/render.c

@@ -1908,6 +1908,8 @@ ProcRenderCreateRadialGradient(ClientPtr client)
     LEGAL_NEW_RESOURCE(stuff->pid, client);
 
     len = (client->req_len << 2) - sizeof(xRenderCreateRadialGradientReq);
+    if (stuff->nStops > UINT32_MAX / (sizeof(xFixed) + sizeof(xRenderColor)))
+        return BadLength;
     if (len != stuff->nStops * (sizeof(xFixed) + sizeof(xRenderColor)))
         return BadLength;
 
@@ -1946,6 +1948,8 @@ ProcRenderCreateConicalGradient(ClientPtr client)
     LEGAL_NEW_RESOURCE(stuff->pid, client);
 
     len = (client->req_len << 2) - sizeof(xRenderCreateConicalGradientReq);
+    if (stuff->nStops > UINT32_MAX / (sizeof(xFixed) + sizeof(xRenderColor)))
+        return BadLength;
     if (len != stuff->nStops * (sizeof(xFixed) + sizeof(xRenderColor)))
         return BadLength;