libmbedcrypto: Fix chacha20-poly1305

Previously, the mbed TLS implementation wouldn't be use at all when
available, being the internal implementation always used instead.

This corrects few bugs and makes the mbed TLS implementation to be used
when ChaCha20 and Poly1305 are available.

This also makes the constant time comparison to be used when checking
the authentication tag.

Signed-off-by: Anderson Toshiyuki Sasaki <ansasaki@redhat.com>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

ConfigureChecks.cmake

@@ -272,6 +272,12 @@ endif (GCRYPT_FOUND)
 if (MBEDTLS_FOUND)
     set(HAVE_LIBMBEDCRYPTO 1)
     set(HAVE_ECC 1)
+
+    set(CMAKE_REQUIRED_INCLUDES "${MBEDTLS_INCLUDE_DIR}/mbedtls")
+    check_include_file(chacha20.h HAVE_MBEDTLS_CHACHA20_H)
+    check_include_file(poly1305.h HAVE_MBEDTLS_POLY1305_H)
+    unset(CMAKE_REQUIRED_INCLUDES)
+
 endif (MBEDTLS_FOUND)
 
 if (CMAKE_USE_PTHREADS_INIT)

src/CMakeLists.txt

@@ -211,10 +211,16 @@ elseif (WITH_MBEDTLS)
         external/fe25519.c
         external/ge25519.c
         external/sc25519.c
-        external/chacha.c
-        external/poly1305.c
-        chachapoly.c
        )
+    if (NOT (HAVE_MBEDTLS_CHACHA20_H AND HAVE_MBEDTLS_POLY1305_H))
+        set(libssh_SRCS
+            ${libssh_SRCS}
+            external/chacha.c
+            external/poly1305.c
+            chachapoly.c
+           )
+    endif()
+
 else (WITH_GCRYPT)
     set(libssh_SRCS
         ${libssh_SRCS}

src/libmbedcrypto.c

@@ -994,9 +994,9 @@ chacha20_poly1305_set_iv(struct ssh_cipher_struct *cipher,
         return SSH_ERROR;
     }
 
-    ret = mbedtls_chacha20_starts(&ctx->header_ctx, seqbuf, 0);
+    ret = mbedtls_chacha20_starts(&ctx->main_ctx, seqbuf, 0);
     if (ret != 0) {
-        SSH_LOG(SSH_LOG_WARNING, "mbedtls_chacha20_starts(header_ctx) failed");
+        SSH_LOG(SSH_LOG_WARNING, "mbedtls_chacha20_starts(main_ctx) failed");
         return SSH_ERROR;
     }
 
@@ -1126,7 +1126,7 @@ chacha20_poly1305_aead_decrypt(struct ssh_cipher_struct *cipher,
 #endif /* DEBUG_CRYPTO */
 
     /* Verify the calculated MAC matches the attached MAC */
-    cmp = memcmp(tag, mac, POLY1305_TAGLEN);
+    cmp = secure_memcmp(tag, mac, POLY1305_TAGLEN);
     if (cmp != 0) {
         /* mac error */
         SSH_LOG(SSH_LOG_PACKET, "poly1305 verify error");
@@ -1187,7 +1187,7 @@ chacha20_poly1305_aead_encrypt(struct ssh_cipher_struct *cipher,
     /* We already did encrypt one block so the counter should be in the correct position */
     ret = mbedtls_chacha20_update(&ctx->main_ctx, len - sizeof(uint32_t),
                                   in_packet->payload, out_packet->payload);
-    if (ret != 1) {
+    if (ret != 0) {
         SSH_LOG(SSH_LOG_WARNING, "mbedtls_chacha20_update failed");
         return;
     }
@@ -1411,7 +1411,7 @@ int ssh_crypto_init(void)
         mbedtls_ctr_drbg_free(&ssh_mbedtls_ctr_drbg);
     }
 
-#if defined(MBEDTLS_CHACHA20_C) && defined(MBEDTLS_POLY1305_C)
+#if !(defined(MBEDTLS_CHACHA20_C) && defined(MBEDTLS_POLY1305_C))
     for (i = 0; ssh_ciphertab[i].name != NULL; i++) {
         int cmp;