Commit message: ECDH downgrade bug fix.

Fix bug where an OpenSSL client would accept a handshake using an
ephemeral ECDH ciphersuites with the server key exchange message omitted.

Thanks to Karthikeyan Bhargavan for reporting this issue.

CVE-2014-3572
Reviewed-by: Matt Caswell <matt@openssl.org>

(cherry picked from commit b15f8769644b00ef7283521593360b7b2135cb63)

Conflicts:
	CHANGES
	ssl/s3_clnt.c
CVE: CVE-2014-3572
CWE: CWE-310
Vulnerability description: The ssl3_get_key_exchange function in s3_clnt.c in OpenSSL before 0.9.8zd, 1.0.0 before 1.0.0p, and 1.0.1 before 1.0.1k allows remote SSL servers to conduct ECDHE-to-ECDH downgrade attacks and trigger a loss of forward secrecy by omitting the ServerKeyExchange message.

Project: openssl

int ssl3_get_key_exchange(SSL *s)
	{
#ifndef OPENSSL_NO_RSA
	unsigned char *q,md_buf[EVP_MAX_MD_SIZE*2];
#endif
	EVP_MD_CTX md_ctx;
	unsigned char *param,*p;
	int al,j,ok;
	long i,param_len,n,alg;
	EVP_PKEY *pkey=NULL;
#ifndef OPENSSL_NO_RSA
	RSA *rsa=NULL;
#endif
#ifndef OPENSSL_NO_DH
	DH *dh=NULL;
#endif
#ifndef OPENSSL_NO_ECDH
	EC_KEY *ecdh = NULL;
	BN_CTX *bn_ctx = NULL;
	EC_POINT *srvr_ecpoint = NULL;
	int curve_nid = 0;
	int encoded_pt_len = 0;
#endif

	/* use same message size as in ssl3_get_certificate_request()
	 * as ServerKeyExchange message may be skipped */
	n=s->method->ssl_get_message(s,
		SSL3_ST_CR_KEY_EXCH_A,
		SSL3_ST_CR_KEY_EXCH_B,
		-1,
		s->max_cert_list,
		&ok);

	if (!ok) return((int)n);

	if (s->s3->tmp.message_type != SSL3_MT_SERVER_KEY_EXCHANGE)
		{
		s->s3->tmp.reuse_message=1;
		return(1);
		}

	param=p=(unsigned char *)s->init_msg;

	if (s->session->sess_cert != NULL)
		{
#ifndef OPENSSL_NO_RSA
		if (s->session->sess_cert->peer_rsa_tmp != NULL)
			{
			RSA_free(s->session->sess_cert->peer_rsa_tmp);
			s->session->sess_cert->peer_rsa_tmp=NULL;
			}
#endif
#ifndef OPENSSL_NO_DH
		if (s->session->sess_cert->peer_dh_tmp)
			{
			DH_free(s->session->sess_cert->peer_dh_tmp);
			s->session->sess_cert->peer_dh_tmp=NULL;
			}
#endif
#ifndef OPENSSL_NO_ECDH
		if (s->session->sess_cert->peer_ecdh_tmp)
			{
			EC_KEY_free(s->session->sess_cert->peer_ecdh_tmp);
			s->session->sess_cert->peer_ecdh_tmp=NULL;
			}
#endif
		}
	else
		{
		s->session->sess_cert=ssl_sess_cert_new();
		}

	/* Total length of the parameters including the length prefix */
	param_len=0;
	alg=s->s3->tmp.new_cipher->algorithms;
	EVP_MD_CTX_init(&md_ctx);

	al=SSL_AD_DECODE_ERROR;
#ifndef OPENSSL_NO_RSA
	if (alg & SSL_kRSA)
		{
		if ((rsa=RSA_new()) == NULL)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,ERR_R_MALLOC_FAILURE);
			goto err;
			}

		param_len = 2;
		if (param_len > n)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,
				SSL_R_LENGTH_TOO_SHORT);
			goto f_err;
			}
		n2s(p,i);

		if (i > n - param_len)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_BAD_RSA_MODULUS_LENGTH);
			goto f_err;
			}
		param_len += i;

		if (!(rsa->n=BN_bin2bn(p,i,rsa->n)))
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,ERR_R_BN_LIB);
			goto err;
			}
		p+=i;

		if (2 > n - param_len)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,
				SSL_R_LENGTH_TOO_SHORT);
			goto f_err;
			}
		param_len += 2;

		n2s(p,i);

		if (i > n - param_len)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_BAD_RSA_E_LENGTH);
			goto f_err;
			}
		param_len += i;

		if (!(rsa->e=BN_bin2bn(p,i,rsa->e)))
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,ERR_R_BN_LIB);
			goto err;
			}
		p+=i;
		n-=param_len;

		/* this should be because we are using an export cipher */
		if (alg & SSL_aRSA)
			pkey=X509_get_pubkey(s->session->sess_cert->peer_pkeys[SSL_PKEY_RSA_ENC].x509);
		else
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,ERR_R_INTERNAL_ERROR);
			goto err;
			}
		s->session->sess_cert->peer_rsa_tmp=rsa;
		rsa=NULL;
		}
#else /* OPENSSL_NO_RSA */
	if (0)
		;
#endif
#ifndef OPENSSL_NO_DH
	else if (alg & SSL_kEDH)
		{
		if ((dh=DH_new()) == NULL)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,ERR_R_DH_LIB);
			goto err;
			}

		param_len = 2;
		if (param_len > n)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,
				SSL_R_LENGTH_TOO_SHORT);
			goto f_err;
			}
		n2s(p,i);

		if (i > n - param_len)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_BAD_DH_P_LENGTH);
			goto f_err;
			}
		param_len += i;

		if (!(dh->p=BN_bin2bn(p,i,NULL)))
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,ERR_R_BN_LIB);
			goto err;
			}
		p+=i;

		if (2 > n - param_len)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,
				SSL_R_LENGTH_TOO_SHORT);
			goto f_err;
			}
		param_len += 2;

		n2s(p,i);

		if (i > n - param_len)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_BAD_DH_G_LENGTH);
			goto f_err;
			}
		param_len += i;

		if (!(dh->g=BN_bin2bn(p,i,NULL)))
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,ERR_R_BN_LIB);
			goto err;
			}
		p+=i;

		if (2 > n - param_len)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,
				SSL_R_LENGTH_TOO_SHORT);
			goto f_err;
			}
		param_len += 2;

		n2s(p,i);

		if (i > n - param_len)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_BAD_DH_PUB_KEY_LENGTH);
			goto f_err;
			}
		param_len += i;

		if (!(dh->pub_key=BN_bin2bn(p,i,NULL)))
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,ERR_R_BN_LIB);
			goto err;
			}
		p+=i;
		n-=param_len;

#ifndef OPENSSL_NO_RSA
		if (alg & SSL_aRSA)
			pkey=X509_get_pubkey(s->session->sess_cert->peer_pkeys[SSL_PKEY_RSA_ENC].x509);
#else
		if (0)
			;
#endif
#ifndef OPENSSL_NO_DSA
		else if (alg & SSL_aDSS)
			pkey=X509_get_pubkey(s->session->sess_cert->peer_pkeys[SSL_PKEY_DSA_SIGN].x509);
#endif
		/* else anonymous DH, so no certificate or pkey. */

		s->session->sess_cert->peer_dh_tmp=dh;
		dh=NULL;
		}
	else if ((alg & SSL_kDHr) || (alg & SSL_kDHd))
		{
		al=SSL_AD_ILLEGAL_PARAMETER;
		SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_TRIED_TO_USE_UNSUPPORTED_CIPHER);
		goto f_err;
		}
#endif /* !OPENSSL_NO_DH */

#ifndef OPENSSL_NO_ECDH
	else if (alg & SSL_kECDHE)
		{
		EC_GROUP *ngroup;
		const EC_GROUP *group;

		if ((ecdh=EC_KEY_new()) == NULL)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,ERR_R_MALLOC_FAILURE);
			goto err;
			}

		/* Extract elliptic curve parameters and the
		 * server's ephemeral ECDH public key.
		 * Keep accumulating lengths of various components in
		 * param_len and make sure it never exceeds n.
		 */

		/* XXX: For now we only support named (not generic) curves
		 * and the ECParameters in this case is just three bytes. We
		 * also need one byte for the length of the encoded point
		 */
		param_len=4;
		if (param_len > n)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,
				SSL_R_LENGTH_TOO_SHORT);
			goto f_err;
			}

		if ((*p != NAMED_CURVE_TYPE) || 
		    ((curve_nid = curve_id2nid(*(p + 2))) == 0))
			{
			al=SSL_AD_INTERNAL_ERROR;
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_UNABLE_TO_FIND_ECDH_PARAMETERS);
			goto f_err;
			}

		ngroup = EC_GROUP_new_by_curve_name(curve_nid);
		if (ngroup == NULL)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,ERR_R_EC_LIB);
			goto err;
			}
		if (EC_KEY_set_group(ecdh, ngroup) == 0)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,ERR_R_EC_LIB);
			goto err;
			}
		EC_GROUP_free(ngroup);

		group = EC_KEY_get0_group(ecdh);

		if (SSL_C_IS_EXPORT(s->s3->tmp.new_cipher) &&
		    (EC_GROUP_get_degree(group) > 163))
			{
			al=SSL_AD_EXPORT_RESTRICTION;
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_ECGROUP_TOO_LARGE_FOR_CIPHER);
			goto f_err;
			}

		p+=3;

		/* Next, get the encoded ECPoint */
		if (((srvr_ecpoint = EC_POINT_new(group)) == NULL) ||
		    ((bn_ctx = BN_CTX_new()) == NULL))
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,ERR_R_MALLOC_FAILURE);
			goto err;
			}

		encoded_pt_len = *p;  /* length of encoded point */
		p+=1;

		if ((encoded_pt_len > n - param_len) ||
		    (EC_POINT_oct2point(group, srvr_ecpoint, 
			p, encoded_pt_len, bn_ctx) == 0))
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_BAD_ECPOINT);
			goto f_err;
			}
		param_len += encoded_pt_len;

		n-=param_len;
		p+=encoded_pt_len;

		/* The ECC/TLS specification does not mention
		 * the use of DSA to sign ECParameters in the server
		 * key exchange message. We do support RSA and ECDSA.
		 */
		if (0) ;
#ifndef OPENSSL_NO_RSA
		else if (alg & SSL_aRSA)
			pkey=X509_get_pubkey(s->session->sess_cert->peer_pkeys[SSL_PKEY_RSA_ENC].x509);
#endif
#ifndef OPENSSL_NO_ECDSA
		else if (alg & SSL_aECDSA)
			pkey=X509_get_pubkey(s->session->sess_cert->peer_pkeys[SSL_PKEY_ECC].x509);
#endif
		/* else anonymous ECDH, so no certificate or pkey. */
		EC_KEY_set_public_key(ecdh, srvr_ecpoint);
		s->session->sess_cert->peer_ecdh_tmp=ecdh;
		ecdh=NULL;
		BN_CTX_free(bn_ctx);
		bn_ctx = NULL;
		EC_POINT_free(srvr_ecpoint);
		srvr_ecpoint = NULL;
		}
	else if (alg & SSL_kECDH)
		{
		al=SSL_AD_UNEXPECTED_MESSAGE;
		SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_UNEXPECTED_MESSAGE);
		goto f_err;
		}
#endif /* !OPENSSL_NO_ECDH */
	if (alg & SSL_aFZA)
		{
		al=SSL_AD_HANDSHAKE_FAILURE;
		SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_TRIED_TO_USE_UNSUPPORTED_CIPHER);
		goto f_err;
		}


	/* p points to the next byte, there are 'n' bytes left */

	/* if it was signed, check the signature */
	if (pkey != NULL)
		{
		n2s(p,i);
		n-=2;
		j=EVP_PKEY_size(pkey);

		/* Check signature length. If n is 0 then signature is empty */
		if ((i != n) || (n > j) || (n <= 0))
			{
			/* wrong packet length */
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_WRONG_SIGNATURE_LENGTH);
			goto f_err;
			}

#ifndef OPENSSL_NO_RSA
		if (pkey->type == EVP_PKEY_RSA)
			{
			int num;
			unsigned int size;

			j=0;
			q=md_buf;
			for (num=2; num > 0; num--)
				{
				EVP_MD_CTX_set_flags(&md_ctx,
					EVP_MD_CTX_FLAG_NON_FIPS_ALLOW);
				EVP_DigestInit_ex(&md_ctx,(num == 2)
					?s->ctx->md5:s->ctx->sha1, NULL);
				EVP_DigestUpdate(&md_ctx,&(s->s3->client_random[0]),SSL3_RANDOM_SIZE);
				EVP_DigestUpdate(&md_ctx,&(s->s3->server_random[0]),SSL3_RANDOM_SIZE);
				EVP_DigestUpdate(&md_ctx,param,param_len);
				EVP_DigestFinal_ex(&md_ctx,q,&size);
				q+=size;
				j+=size;
				}
			i=RSA_verify(NID_md5_sha1, md_buf, j, p, n,
								pkey->pkey.rsa);
			if (i < 0)
				{
				al=SSL_AD_DECRYPT_ERROR;
				SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_BAD_RSA_DECRYPT);
				goto f_err;
				}
			if (i == 0)
				{
				/* bad signature */
				al=SSL_AD_DECRYPT_ERROR;
				SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_BAD_SIGNATURE);
				goto f_err;
				}
			}
		else
#endif
#ifndef OPENSSL_NO_DSA
			if (pkey->type == EVP_PKEY_DSA)
			{
			/* lets do DSS */
			EVP_VerifyInit_ex(&md_ctx,EVP_dss1(), NULL);
			EVP_VerifyUpdate(&md_ctx,&(s->s3->client_random[0]),SSL3_RANDOM_SIZE);
			EVP_VerifyUpdate(&md_ctx,&(s->s3->server_random[0]),SSL3_RANDOM_SIZE);
			EVP_VerifyUpdate(&md_ctx,param,param_len);
			if (EVP_VerifyFinal(&md_ctx,p,(int)n,pkey) <= 0)
				{
				/* bad signature */
				al=SSL_AD_DECRYPT_ERROR;
				SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_BAD_SIGNATURE);
				goto f_err;
				}
			}
		else
#endif
#ifndef OPENSSL_NO_ECDSA
			if (pkey->type == EVP_PKEY_EC)
			{
			/* let's do ECDSA */
			EVP_VerifyInit_ex(&md_ctx,EVP_ecdsa(), NULL);
			EVP_VerifyUpdate(&md_ctx,&(s->s3->client_random[0]),SSL3_RANDOM_SIZE);
			EVP_VerifyUpdate(&md_ctx,&(s->s3->server_random[0]),SSL3_RANDOM_SIZE);
			EVP_VerifyUpdate(&md_ctx,param,param_len);
			if (EVP_VerifyFinal(&md_ctx,p,(int)n,pkey) <= 0)
				{
				/* bad signature */
				al=SSL_AD_DECRYPT_ERROR;
				SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_BAD_SIGNATURE);
				goto f_err;
				}
			}
		else
#endif
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,ERR_R_INTERNAL_ERROR);
			goto err;
			}
		}
	else
		{
		/* still data left over */
		if (!(alg & SSL_aNULL))
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,ERR_R_INTERNAL_ERROR);
			goto err;
			}
		if (n != 0)
			{
			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_EXTRA_DATA_IN_MESSAGE);
			goto f_err;
			}
		}
	EVP_PKEY_free(pkey);
	EVP_MD_CTX_cleanup(&md_ctx);
	return(1);
f_err:
	ssl3_send_alert(s,SSL3_AL_FATAL,al);
err:
	EVP_PKEY_free(pkey);
#ifndef OPENSSL_NO_RSA
	if (rsa != NULL)
		RSA_free(rsa);
#endif
#ifndef OPENSSL_NO_DH
	if (dh != NULL)
		DH_free(dh);
#endif
#ifndef OPENSSL_NO_ECDH
	BN_CTX_free(bn_ctx);
	EC_POINT_free(srvr_ecpoint);
	if (ecdh != NULL)
		EC_KEY_free(ecdh);
#endif
	EVP_MD_CTX_cleanup(&md_ctx);
	return(-1);
	}