From 7a8f683cedf9b0d1024a80362693c9f8b93a0f2b Mon Sep 17 00:00:00 2001 From: TJ Saunders Date: Thu, 10 Mar 2016 15:07:58 -0800 Subject: [PATCH] Backport of fix for Bug#4230 to 1.3.5 branch. Upstream-Status: Backport CVE: CVE-2016-3125 Author: TJ Saunders Signed-off-by: Catalin Enache --- contrib/mod_tls.c | 167 +++++++++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 147 insertions(+), 20 deletions(-) diff --git a/contrib/mod_tls.c b/contrib/mod_tls.c index df92658..5883cc7 100644 --- a/contrib/mod_tls.c +++ b/contrib/mod_tls.c @@ -411,6 +411,13 @@ static int tls_required_on_ctrl = 0; static int tls_required_on_data = 0; static unsigned char *tls_authenticated = NULL; +/* Define the minimum DH group length we allow (unless the AllowWeakDH + * TLSOption is used). Ideally this would be 2048, per https://weakdh.org, + * but for compatibility with older Java versions, which only support up to + * 1024, we'll use 1024. For now. + */ +#define TLS_DH_MIN_LEN 1024 + /* mod_tls session flags */ #define TLS_SESS_ON_CTRL 0x0001 #define TLS_SESS_ON_DATA 0x0002 @@ -438,6 +445,7 @@ static unsigned char *tls_authenticated = NULL; #define TLS_OPT_USE_IMPLICIT_SSL 0x0200 #define TLS_OPT_ALLOW_CLIENT_RENEGOTIATIONS 0x0400 #define TLS_OPT_VERIFY_CERT_CN 0x0800 +#define TLS_OPT_ALLOW_WEAK_DH 0x1000 /* mod_tls SSCN modes */ #define TLS_SSCN_MODE_SERVER 0 @@ -2417,24 +2425,139 @@ static int tls_ctrl_renegotiate_cb(CALLBACK_FRAME) { static DH *tls_dh_cb(SSL *ssl, int is_export, int keylength) { DH *dh = NULL; + EVP_PKEY *pkey; + int pkeylen = 0, use_pkeylen = FALSE; + + /* OpenSSL will only ever call us (currently) with a keylen of 512 or 1024; + * see the SSL_EXPORT_PKEYLENGTH macro in ssl_locl.h. Sigh. + * + * Thus we adjust the DH parameter length according to the size of the + * RSA/DSA private key used for the current connection. + * + * NOTE: This MAY cause interoperability issues with some clients, notably + * Java 7 (and earlier) clients, since Java 7 and earlier supports + * Diffie-Hellman only up to 1024 bits. More sighs. To deal with these + * clients, then, you need to configure a certificate/key of 1024 bits. + */ + pkey = SSL_get_privatekey(ssl); + if (pkey != NULL) { + if (EVP_PKEY_type(pkey->type) == EVP_PKEY_RSA || + EVP_PKEY_type(pkey->type) == EVP_PKEY_DSA) { + pkeylen = EVP_PKEY_bits(pkey); + + if (pkeylen < TLS_DH_MIN_LEN) { + if (!(tls_opts & TLS_OPT_ALLOW_WEAK_DH)) { + pr_trace_msg(trace_channel, 11, + "certificate private key length %d less than %d bits, using %d " + "(see AllowWeakDH TLSOption)", pkeylen, TLS_DH_MIN_LEN, + TLS_DH_MIN_LEN); + pkeylen = TLS_DH_MIN_LEN; + } + } + + if (pkeylen != keylen) { + pr_trace_msg(trace_channel, 13, + "adjusted DH parameter length from %d to %d bits", keylen, pkeylen); + use_pkeylen = TRUE; + } + } + } if (tls_tmp_dhs != NULL && tls_tmp_dhs->nelts > 0) { register unsigned int i; - DH **dhs; + DH *best_dh = NULL, **dhs; + int best_dhlen = 0; dhs = tls_tmp_dhs->elts; + + /* Search the configured list of DH parameters twice: once for any sizes + * matching the actual requested size (usually 1024), and once for any + * matching the certificate private key size (pkeylen). + * + * This behavior allows site admins to configure a TLSDHParamFile that + * contains 1024-bit parameters, for e.g. Java 7 (and earlier) clients. + */ + + /* Note: the keylen argument is in BITS, but DH_size() returns the number + * of BYTES. + */ for (i = 0; i < tls_tmp_dhs->nelts; i++) { - /* Note: the keylength argument is in BITS, but DH_size() returns - * the number of BYTES. + int dhlen; + + dhlen = DH_size(dhs[i]) * 8; + if (dhlen == keylen) { + pr_trace_msg(trace_channel, 11, + "found matching DH parameter for key length %d", keylen); + return dhs[i]; + } + + /* Try to find the next "best" DH to use, where "best" means + * the smallest DH that is larger than the necessary keylen. */ - if (DH_size(dhs[i]) == (keylength / 8)) { + if (dhlen > keylen) { + if (best_dh != NULL) { + if (dhlen < best_dhlen) { + best_dh = dhs[i]; + best_dhlen = dhlen; + } + + } else { + best_dh = dhs[i]; + best_dhlen = dhlen; + } + } + } + + for (i = 0; i < tls_tmp_dhs->nelts; i++) { + int dhlen; + + dhlen = DH_size(dhs[i]) * 8; + if (dhlen == pkeylen) { + pr_trace_msg(trace_channel, 11, + "found matching DH parameter for certificate private key length %d", + pkeylen); return dhs[i]; } + + if (dhlen > pkeylen) { + if (best_dh != NULL) { + if (dhlen < best_dhlen) { + best_dh = dhs[i]; + best_dhlen = dhlen; + } + + } else { + best_dh = dhs[i]; + best_dhlen = dhlen; + } + } + } + + if (best_dh != NULL) { + pr_trace_msg(trace_channel, 11, + "using best DH parameter for key length %d (length %d)", keylen, + best_dhlen); + return best_dh; } } - switch (keylength) { + /* Still no DH parameters found? Use the built-in ones. */ + + if (keylen < TLS_DH_MIN_LEN) { + if (!(tls_opts & TLS_OPT_ALLOW_WEAK_DH)) { + pr_trace_msg(trace_channel, 11, + "requested key length %d less than %d bits, using %d " + "(see AllowWeakDH TLSOption)", keylen, TLS_DH_MIN_LEN, TLS_DH_MIN_LEN); + keylen = TLS_DH_MIN_LEN; + } + } + + if (use_pkeylen) { + keylen = pkeylen; + } + + switch (keylen) { case 512: dh = get_dh512(); break; @@ -2443,32 +2566,33 @@ static DH *tls_dh_cb(SSL *ssl, int is_export, int keylength) { dh = get_dh768(); break; - case 1024: - dh = get_dh1024(); - break; + case 1024: + dh = get_dh1024(); + break; - case 1536: - dh = get_dh1536(); - break; + case 1536: + dh = get_dh1536(); + break; - case 2048: - dh = get_dh2048(); - break; + case 2048: + dh = get_dh2048(); + break; - default: - tls_log("unsupported DH key length %d requested, returning 1024 bits", - keylength); - dh = get_dh1024(); - break; + default: + tls_log("unsupported DH key length %d requested, returning 1024 bits", + keylen); + dh = get_dh1024(); + break; } + pr_trace_msg(trace_channel, 11, "using builtin DH for %d bits", keylen); + /* Add this DH to the list, so that it can be freed properly later. */ if (tls_tmp_dhs == NULL) { tls_tmp_dhs = make_array(session.pool, 1, sizeof(DH *)); } *((DH **) push_array(tls_tmp_dhs)) = dh; - return dh; } @@ -8445,6 +8569,9 @@ MODRET set_tlsoptions(cmd_rec *cmd) { strcmp(cmd->argv[i], "AllowClientRenegotiations") == 0) { opts |= TLS_OPT_ALLOW_CLIENT_RENEGOTIATIONS; + } else if (strcmp(cmd->argv[i], "AllowWeakDH") == 0) { + opts |= TLS_OPT_ALLOW_WEAK_DH; + } else if (strcmp(cmd->argv[i], "EnableDiags") == 0) { opts |= TLS_OPT_ENABLE_DIAGS; -- 2.7.4