Fix MD5 and SHA buffer overrun.

Author: philljj

wolfcrypt/src/md5.c

@@ -461,7 +461,9 @@ int wc_Md5Final(wc_Md5* md5, byte* hash)
 
     /* pad with zeros */
     if (md5->buffLen > WC_MD5_PAD_SIZE) {
-        XMEMSET(&local[md5->buffLen], 0, WC_MD5_BLOCK_SIZE - md5->buffLen);
+        if (md5->buffLen < WC_MD5_BLOCK_SIZE) {
+            XMEMSET(&local[md5->buffLen], 0, WC_MD5_BLOCK_SIZE - md5->buffLen);
+        }
         md5->buffLen += WC_MD5_BLOCK_SIZE - md5->buffLen;
 
 #if defined(BIG_ENDIAN_ORDER) && !defined(FREESCALE_MMCAU_SHA)

wolfcrypt/src/sha256.c

@@ -1321,8 +1321,11 @@ static int InitSha256(wc_Sha256* sha256)
 
         /* pad with zeros */
         if (sha256->buffLen > WC_SHA256_PAD_SIZE) {
-            XMEMSET(&local[sha256->buffLen], 0,
-                WC_SHA256_BLOCK_SIZE - sha256->buffLen);
+            if (sha256->buffLen < WC_SHA256_BLOCK_SIZE) {
+                XMEMSET(&local[sha256->buffLen], 0,
+                    WC_SHA256_BLOCK_SIZE - sha256->buffLen);
+            }
+
             sha256->buffLen += WC_SHA256_BLOCK_SIZE - sha256->buffLen;
 
         #if defined(WOLFSSL_USE_ESP32_CRYPT_HASH_HW) && \

wolfcrypt/src/sha512.c

@@ -942,7 +942,11 @@ static WC_INLINE int Sha512Final(wc_Sha512* sha512)
 
     /* pad with zeros */
     if (sha512->buffLen > WC_SHA512_PAD_SIZE) {
-        XMEMSET(&local[sha512->buffLen], 0, WC_SHA512_BLOCK_SIZE - sha512->buffLen);
+        if (sha512->buffLen < WC_SHA512_BLOCK_SIZE ) {
+            XMEMSET(&local[sha512->buffLen], 0,
+                WC_SHA512_BLOCK_SIZE - sha512->buffLen);
+        }
+
         sha512->buffLen += WC_SHA512_BLOCK_SIZE - sha512->buffLen;
 #if defined(LITTLE_ENDIAN_ORDER)
     #if defined(USE_INTEL_SPEEDUP) && \