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Fix certificate generation with mbedtls 2.16.8 . 

When generating certificates with
`Crypto.generate_self_signed_certificate` we generate the PEM in a
buffer via `mbedtls_x509write_crt_pem`.

Since version 2.16.8, mbedtls adds spurious data at the end of the
buffer due to internal optimizations, this breaks our logic when we try
to immediately parse it and return a proper `X509Certificate` object.

This commit updates the code to find the actual PEM length to parse
using `strlen`, takes extra caution always adding the terminator to the
buffer, and slightly improve error messages.
This commit is contained in:
Fabio Alessandrelli 2020-09-15 18:47:51 +02:00
parent 7f0352b4d1
commit 60687ce778
1 changed files with 8 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
modules/mbedtls/crypto_mbedtls.cpp
View File

@ -43,8 +43,8 @@
#define PEM_BEGIN_CRT "-----BEGIN CERTIFICATE-----\n" #define PEM_BEGIN_CRT "-----BEGIN CERTIFICATE-----\n"
#define PEM_END_CRT "-----END CERTIFICATE-----\n" #define PEM_END_CRT "-----END CERTIFICATE-----\n"
#include "mbedtls/pem.h"
#include <mbedtls/debug.h> #include <mbedtls/debug.h>
#include <mbedtls/pem.h>
CryptoKey *CryptoKeyMbedTLS::create() { CryptoKey *CryptoKeyMbedTLS::create() {
return memnew(CryptoKeyMbedTLS); return memnew(CryptoKeyMbedTLS);
@ -294,20 +294,15 @@ Ref<X509Certificate> CryptoMbedTLS::generate_self_signed_certificate(Ref<CryptoK
unsigned char buf[4096]; unsigned char buf[4096];
memset(buf, 0, 4096); memset(buf, 0, 4096);
int ret = mbedtls_x509write_crt_pem(&crt, buf, 4096, mbedtls_ctr_drbg_random, &ctr_drbg);
mbedtls_mpi_free(&serial);
mbedtls_x509write_crt_free(&crt);
ERR_FAIL_COND_V_MSG(ret != 0, nullptr, "Failed to generate certificate: " + itos(ret));
buf[4095] = '\0'; // Make sure strlen can't fail.
Ref<X509CertificateMbedTLS> out; Ref<X509CertificateMbedTLS> out;
out.instance(); out.instance();
mbedtls_x509write_crt_pem(&crt, buf, 4096, mbedtls_ctr_drbg_random, &ctr_drbg); out->load_from_memory(buf, strlen((char *)buf) + 1); // Use strlen to find correct output size.
int err = mbedtls_x509_crt_parse(&(out->cert), buf, 4096);
if (err != 0) {
mbedtls_mpi_free(&serial);
mbedtls_x509write_crt_free(&crt);
ERR_PRINT("Generated invalid certificate: " + itos(err));
return nullptr;
}
mbedtls_mpi_free(&serial);
mbedtls_x509write_crt_free(&crt);
return out; return out;
} }