The main motivation to make this change is to avoid a crash in mbed TLS 2.25 with --verb < 8.
mbed TLS 2.25 has a nasty bug that the print function for Montgomery style EC curves (Curve25519 and Curve448) does segfault. See also the issue reported here: https://github.com/ARMmbed/mbedtls/issues/4208 We request always debug level 3 from mbed TLS but filter out any debug output of level 3 unless verb 8 or higher is set. This commeit sets the debug level to 2 to avoid this problem by makeing mbed TLS not generatin the problematic debug output. For the affected version to still use --verb 8 with mbed TLS 2.25 is to restrict the EC groups to ones that do not crash the print function like with '--tls-groups secp521r1:secp384r1:secp256r1'. This patch has no patch on user-visible behaviour on unaffected mbed TLS versions. Signed-off-by: Arne Schwabe <a...@rfc2549.org> Patch V2: Replace magic constant with proper define. Highlight more this avoding generating unessary debug output than crash workaround. --- src/openvpn/options.c | 6 ++++++ src/openvpn/ssl_common.h | 1 + src/openvpn/ssl_mbedtls.c | 13 ++++++++++++- 3 files changed, 19 insertions(+), 1 deletion(-) diff --git a/src/openvpn/options.c b/src/openvpn/options.c index 0eb049d8..c4646d48 100644 --- a/src/openvpn/options.c +++ b/src/openvpn/options.c @@ -5883,6 +5883,12 @@ add_option(struct options *options, { VERIFY_PERMISSION(OPT_P_MESSAGES); options->verbosity = positive_atoi(p[1]); + if (options->verbosity >= (D_TLS_DEBUG_MED & M_DEBUG_LEVEL)) + { + /* We pass this flag to the SSL library to avoid a + * mbed TLS always generating debug level logging */ + options->ssl_flags |= SSLF_TLS_DEBUG_ENABLED; + } #if !defined(ENABLE_DEBUG) && !defined(ENABLE_SMALL) /* Warn when a debug verbosity is supplied when built without debug support */ if (options->verbosity >= 7) diff --git a/src/openvpn/ssl_common.h b/src/openvpn/ssl_common.h index b493cbb7..2e3c98db 100644 --- a/src/openvpn/ssl_common.h +++ b/src/openvpn/ssl_common.h @@ -352,6 +352,7 @@ struct tls_options #define SSLF_TLS_VERSION_MIN_MASK 0xF /* (uses bit positions 6 to 9) */ #define SSLF_TLS_VERSION_MAX_SHIFT 10 #define SSLF_TLS_VERSION_MAX_MASK 0xF /* (uses bit positions 10 to 13) */ +#define SSLF_TLS_DEBUG_ENABLED (1<<14) unsigned int ssl_flags; #ifdef ENABLE_MANAGEMENT diff --git a/src/openvpn/ssl_mbedtls.c b/src/openvpn/ssl_mbedtls.c index b30b6b9d..4626e983 100644 --- a/src/openvpn/ssl_mbedtls.c +++ b/src/openvpn/ssl_mbedtls.c @@ -1058,7 +1058,18 @@ key_state_ssl_init(struct key_state_ssl *ks_ssl, mbedtls_ssl_config_defaults(ks_ssl->ssl_config, ssl_ctx->endpoint, MBEDTLS_SSL_TRANSPORT_STREAM, MBEDTLS_SSL_PRESET_DEFAULT); #ifdef MBEDTLS_DEBUG_C - mbedtls_debug_set_threshold(3); + /* We only want to have mbed TLS generate debug level logging when we would + * also display it. + * In fact mbed TLS 2.25.0 crashes generating debug log if Curve25591 is + * selected for DH (https://github.com/ARMmbed/mbedtls/issues/4208) */ + if (session->opt->ssl_flags & SSLF_TLS_DEBUG_ENABLED) + { + mbedtls_debug_set_threshold(3); + } + else + { + mbedtls_debug_set_threshold(2); + } #endif mbedtls_ssl_conf_dbg(ks_ssl->ssl_config, my_debug, NULL); mbedtls_ssl_conf_rng(ks_ssl->ssl_config, mbedtls_ctr_drbg_random, -- 2.30.1 _______________________________________________ Openvpn-devel mailing list Openvpn-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/openvpn-devel
