rpcrt4: Introduce a new function, safe_multiply, which will raise an

exception if a multiply overflows a 4-byte integer.

This will protect the unmarshaling code against attacks specifying a 
large variance.
Use this new function in the conformant string functions to harden them 
against attack.

dlls/rpcrt4/ndr_marshall.c

@@ -518,6 +518,19 @@ finish_conf:
     return pFormat+4;
 }
 
+/* multiply two numbers together, raising an RPC_S_INVALID_BOUND exception if
+ * the result overflows 32-bits */
+static ULONG inline safe_multiply(ULONG a, ULONG b)
+{
+    ULONGLONG ret = (ULONGLONG)a * b;
+    if (ret > 0xffffffff)
+    {
+        RpcRaiseException(RPC_S_INVALID_BOUND);
+        return 0;
+    }
+    return ret;
+}
+
 
 /*
  * NdrConformantString:
@@ -542,7 +555,7 @@ finish_conf:
 unsigned char *WINAPI NdrConformantStringMarshall(MIDL_STUB_MESSAGE *pStubMsg,
   unsigned char *pszMessage, PFORMAT_STRING pFormat)
 { 
-  unsigned long esize;
+  ULONG esize, size;
 
   TRACE("(pStubMsg == ^%p, pszMessage == ^%p, pFormat == ^%p)\n", pStubMsg, pszMessage, pFormat);
   
@@ -570,8 +583,9 @@ unsigned char *WINAPI NdrConformantStringMarshall(MIDL_STUB_MESSAGE *pStubMsg,
   WriteConformance(pStubMsg);
   WriteVariance(pStubMsg);
 
-  memcpy(pStubMsg->Buffer, pszMessage, pStubMsg->ActualCount*esize); /* the string itself */
+  size = safe_multiply(esize, pStubMsg->ActualCount);
-  pStubMsg->Buffer += pStubMsg->ActualCount*esize;
+  memcpy(pStubMsg->Buffer, pszMessage, size); /* the string itself */
+  pStubMsg->Buffer += size;
 
   STD_OVERFLOW_CHECK(pStubMsg);
 
@@ -585,25 +599,35 @@ unsigned char *WINAPI NdrConformantStringMarshall(MIDL_STUB_MESSAGE *pStubMsg,
 void WINAPI NdrConformantStringBufferSize(PMIDL_STUB_MESSAGE pStubMsg,
   unsigned char* pMemory, PFORMAT_STRING pFormat)
 {
+  ULONG esize;
+
   TRACE("(pStubMsg == ^%p, pMemory == ^%p, pFormat == ^%p)\n", pStubMsg, pMemory, pFormat);
 
   SizeConformance(pStubMsg);
   SizeVariance(pStubMsg);
 
   if (*pFormat == RPC_FC_C_CSTRING) {
-    /* we need + 1 octet for '\0' */
     TRACE("string=%s\n", debugstr_a((char*)pMemory));
-    pStubMsg->BufferLength += strlen((char*)pMemory) + 1;
+    pStubMsg->ActualCount = strlen((char*)pMemory)+1;
+    esize = 1;
   }
   else if (*pFormat == RPC_FC_C_WSTRING) {
-    /* we need + 2 octets for L'\0' */
     TRACE("string=%s\n", debugstr_w((LPWSTR)pMemory));
-    pStubMsg->BufferLength += strlenW((LPWSTR)pMemory)*2 + 2;
+    pStubMsg->ActualCount = strlenW((LPWSTR)pMemory)+1;
+    esize = 2;
   }
   else {
     ERR("Unhandled string type: %#x\n", *pFormat); 
     /* FIXME: raise an exception */
+    return;
   }
+
+  if (pFormat[1] == RPC_FC_STRING_SIZED)
+    pFormat = ComputeConformance(pStubMsg, pMemory, pFormat + 2, 0);
+  else
+    pStubMsg->MaxCount = pStubMsg->ActualCount;
+
+  pStubMsg->BufferLength += safe_multiply(esize, pStubMsg->ActualCount);
 }
 
 /************************************************************************
@@ -643,7 +667,7 @@ unsigned long WINAPI NdrConformantStringMemorySize( PMIDL_STUB_MESSAGE pStubMsg,
 unsigned char *WINAPI NdrConformantStringUnmarshall( PMIDL_STUB_MESSAGE pStubMsg,
   unsigned char** ppMemory, PFORMAT_STRING pFormat, unsigned char fMustAlloc )
 {
-  unsigned long len, esize;
+  unsigned long size, esize;
 
   TRACE("(pStubMsg == ^%p, *pMemory == ^%p, pFormat == ^%p, fMustAlloc == %u)\n",
     pStubMsg, *ppMemory, pFormat, fMustAlloc);
@@ -661,14 +685,14 @@ unsigned char *WINAPI NdrConformantStringUnmarshall( PMIDL_STUB_MESSAGE pStubMsg
     esize = 0;
   }
 
-  len = pStubMsg->ActualCount;
+  size = safe_multiply(esize, pStubMsg->ActualCount);
 
   if (fMustAlloc || !*ppMemory)
-    *ppMemory = NdrAllocate(pStubMsg, len*esize);
+    *ppMemory = NdrAllocate(pStubMsg, size);
 
-  memcpy(*ppMemory, pStubMsg->Buffer, len*esize);
+  memcpy(*ppMemory, pStubMsg->Buffer, size);
 
-  pStubMsg->Buffer += len*esize;
+  pStubMsg->Buffer += size;
 
   if (*pFormat == RPC_FC_C_CSTRING) {
     TRACE("string=%s\n", debugstr_a((char*)*ppMemory));