Merge pull request #732 from gabor-mezei-arm/689_bp216_zeroising_of_plaintext_buffers

[Backport 2.16] Zeroising of plaintext buffers in mbedtls_ssl_read()

library/ssl_tls.c

@@ -8656,6 +8656,10 @@ int mbedtls_ssl_read( mbedtls_ssl_context *ssl, unsigned char *buf, size_t len )
     memcpy( buf, ssl->in_offt, n );
     ssl->in_msglen -= n;
 
+    /* Zeroising the plaintext buffer to erase unused application data
+       from the memory. */
+    mbedtls_platform_zeroize( ssl->in_offt, n );
+
     if( ssl->in_msglen == 0 )
     {
         /* all bytes consumed */