b0f6e9a3d7 — curl

Subject

openssl channel_binding: lookup digest algorithm without NID

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Architecture & Compiler Flags

Architecture: x86_64-linux-gnu Compiler: gcc (Ubuntu 11.4.0-1ubuntu1~22.04.3) 11.4.0

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Commit Diff GitHub →

lib/vtls/openssl.c +82 -15

lib/vtls/openssl.c+82 -15

@@ -5255,13 +5255,15 @@ out:
	return result;
	}

-	static CURLcode ossl_get_channel_binding(struct Curl_easy *data, int sockindex,
+	static CURLcode ossl_get_channel_binding(struct Curl_easy *data,
+	int sockindex,
	struct dynbuf *binding)
	{
	X509 *cert;
-	int algo_nid;
-	const EVP_MD *algo_type;
-	const char *algo_name;
+	int mdnid;
+	bool no_digest_acceptable = FALSE;
+	const EVP_MD *algo_type = NULL;
+	const char *algo_name = NULL;
	unsigned int length;
	unsigned char buf[EVP_MAX_MD_SIZE];

@@ -5293,43 +5295,108 @@ static CURLcode ossl_get_channel_binding(struct Curl_easy *data, int sockindex,
	/* No server certificate, do not do channel binding */
	return CURLE_OK;

-	if(!OBJ_find_sigid_algs(X509_get_signature_nid(cert), &algo_nid, NULL)) {
+	#ifdef HAVE_OPENSSL3
+	{
+	int pknid, secbits;
+	uint32_t flags;
+	EVP_PKEY *pkey = X509_get0_pubkey(cert);
+
+	if(!X509_get_signature_info(cert, &mdnid, &pknid, &secbits, &flags)) {
+	failf(data, "certificate signature algorithm not recognized");
+	result = CURLE_SSL_INVALIDCERTSTATUS;
+	goto out;
+	}
+
+	if(mdnid != NID_undef) {
+	if(mdnid == NID_md5 \|\| mdnid == NID_sha1) {
+	algo_type = EVP_sha256();
+	}
+	else
+	algo_type = EVP_get_digestbynid(mdnid);
+	}
+	else if(pkey && !EVP_PKEY_is_a(pkey, OBJ_nid2sn(pknid))) {
+	/* The cert's pkey is different from the algorithm used to sign
+	* the certificate. Since the reported `mdnid` is undefined, there
+	* is no digest algorithm available here. This happens in PQC
+	* and is accepted, resulting in no addition to the binding. */
+	no_digest_acceptable = TRUE;
+	}
+	else if(pkey) {
+	/* cert's pkey type is the same as the cert signer (or same family).
+	* Ask for the mandatory/advisory digest algorithm for the pkey.
+	*/
+	char mdname[128] = "";
+	int rc = EVP_PKEY_get_default_digest_name(pkey, mdname, sizeof(mdname));
+	bool md_is_undef = !strcmp(mdname, "UNDEF");
+
+	if(rc == 2 && md_is_undef) {
+	/* OpenSSL declares "undef" the mandatory digest for this key.
+	* This is some PQC shit, accept it, no addition to binding. */
+	no_digest_acceptable = TRUE;
+	}
+	else if(rc > 0 && mdname[0] != '\0' && !md_is_undef) {
+	infof(data, "Digest algorithm : %s%s (derived from public key)"
+	", but unavailable",
+	mdname, rc == 2 ? " [mandatory]" : " [advisory]");
+	}
+	}
+	}
+	#else /* HAVE_OPENSSL3 */
+
+	if(!OBJ_find_sigid_algs(X509_get_signature_nid(cert), &mdnid, NULL)) {
	failf(data,
	"Unable to find digest NID for certificate signature algorithm");
	result = CURLE_SSL_INVALIDCERTSTATUS;
-	goto error;
+	goto out;
	}

	/* https://datatracker.ietf.org/doc/html/rfc5929#section-4.1 */
-	if(algo_nid == NID_md5 \|\| algo_nid == NID_sha1) {
+	if(mdnid == NID_md5 \|\| mdnid == NID_sha1) {
	algo_type = EVP_sha256();
	}
	else {
-	algo_type = EVP_get_digestbynid(algo_nid);
+	algo_type = EVP_get_digestbynid(mdnid);
	if(!algo_type) {
-	algo_name = OBJ_nid2sn(algo_nid);
+	algo_name = OBJ_nid2sn(mdnid);
	failf(data, "Could not find digest algorithm %s (NID %d)",
-	algo_name ? algo_name : "(null)", algo_nid);
+	algo_name ? algo_name : "(null)", mdnid);
	result = CURLE_SSL_INVALIDCERTSTATUS;
-	goto error;
+	goto out;
+	}
+	}
+
+	#endif /* HAVE_OPENSSL3, else */
+
+	if(!algo_type) {
+	if(no_digest_acceptable) {
+	infof(data, "certificate exposes no signing digest algorithm, "
+	"nothing to add to channel binding");
+	result = CURLE_OK;
+	goto out;
	}
+	/* unacceptable, something is wrong, fail */
+	algo_name = OBJ_nid2sn(mdnid);
+	failf(data, "Unable to find digest algorithm %s (NID %d) "
+	"for channel binding", algo_name ? algo_name : "(null)", mdnid);
+	result = CURLE_SSL_INVALIDCERTSTATUS;
+	goto out;
	}

	if(!X509_digest(cert, algo_type, buf, &length)) {
-	failf(data, "X509_digest() failed");
+	failf(data, "X509_digest() failed for channel binding");
	result = CURLE_SSL_INVALIDCERTSTATUS;
-	goto error;
+	goto out;
	}

	/* Append "tls-server-end-point:" */
	result = curlx_dyn_addn(binding, prefix, sizeof(prefix) - 1);
	if(result)
-	goto error;
+	goto out;

	/* Append digest */
	result = curlx_dyn_addn(binding, buf, length);

-	error:
+	out:
	X509_free(cert);
	return result;
	}