buffer: use size_t instead of uint32_t to avoid segmentation fault

Fixes: #46836
PR-URL: #48033
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Minwoo Jung <nodecorelab@gmail.com>
Reviewed-By: Shelley Vohr <shelley.vohr@gmail.com>
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>

src/string_bytes.cc

@@ -627,11 +627,11 @@ size_t StringBytes::hex_encode(
     char* dst,
     size_t dlen) {
   // We know how much we'll write, just make sure that there's space.
-  CHECK(dlen >= slen * 2 &&
-      "not enough space provided for hex encode");
+  CHECK(dlen >= MultiplyWithOverflowCheck<size_t>(slen, 2u) &&
+        "not enough space provided for hex encode");
 
   dlen = slen * 2;
-  for (uint32_t i = 0, k = 0; k < dlen; i += 1, k += 2) {
+  for (size_t i = 0, k = 0; k < dlen; i += 1, k += 2) {
     static const char hex[] = "0123456789abcdef";
     uint8_t val = static_cast<uint8_t>(src[i]);
     dst[k + 0] = hex[val >> 4];