Minor fix in liboqs GetRandomData

Fixes F-4443

wolfcrypt/src/port/liboqs/liboqs.c

@@ -49,7 +49,14 @@ static void wolfSSL_liboqsGetRandomData(uint8_t* buffer, size_t numOfBytes)
 
     while (numOfBytes > 0) {
         numOfBytes_word32 = (word32)numOfBytes;
-        numOfBytes -= numOfBytes_word32;
+        /* On platforms where size_t is wider than word32, the cast above can
+         * truncate. If numOfBytes does not fit into a word32 (including the
+         * case where it is an exact multiple of 2^32 and truncates to 0),
+         * generate the largest chunk that fits to guarantee forward progress
+         * and avoid an infinite loop. */
+        if ((size_t)numOfBytes_word32 != numOfBytes) {
+            numOfBytes_word32 = 0xFFFFFFFFU;
+        }
         ret = wc_RNG_GenerateBlock(liboqsCurrentRNG, buffer,
                                    numOfBytes_word32);
         if (ret != 0) {
@@ -62,6 +69,10 @@ static void wolfSSL_liboqsGetRandomData(uint8_t* buffer, size_t numOfBytes)
                 );
             abort();
         }
+        /* Advance the buffer so subsequent iterations append rather than
+         * overwrite the previously generated bytes. */
+        buffer += numOfBytes_word32;
+        numOfBytes -= numOfBytes_word32;
     }
 }