From: Steffan Karger Date: Sat, 28 Nov 2015 10:38:24 +0000 (+0100) Subject: openssl: properly check return value of RAND_bytes() X-Git-Tag: v2.3.9~15 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ee714263892068171181e683aef9bc5e9dcac54a;p=thirdparty%2Fopenvpn.git openssl: properly check return value of RAND_bytes() This patch is in response to an off-list report by Sebastian Krahmer of the SuSE security team. Sebastian noticed we do not check the return value of RAND_bytes() correctly. The RAND_bytes() man page first says "RAND_bytes() returns 1 on success, 0 otherwise.", but then a bit later "Both functions return -1 if they are not supported by the current RAND method.". This second case was not covered by our return value checking. Note that if RAND_bytes() would return -1, it would *always* return -1 and fail to generate random. Also note that if RAND_bytes() would return -1, it would do so too in the openssl internal ssl funtions. The openssl internal function do check the return value properly, and connection setup would fail all together. If that would be at least somewhat common, we would have received a *lot* of bug reports. In other words, the error affects static key setups only, and seems highly unlikely to occur in actual setups. Only builds using OpenSSL as the crypto backend are affected. This patch: 1. Changes the behaviour of rand_bytes() in openssl builds to match what the doxygen claims (and polarssl builds already do). 2. Adds error reporting for RAND_bytes() failures. Note: crypto_msg() was changed to msg() for 2.3 Signed-off-by: Steffan Karger Acked-by: Arne Schwabe Acked-by: Gert Doering Message-Id: <1448707105-10753-1-git-send-email-steffan@karger.me> URL: http://article.gmane.org/gmane.network.openvpn.devel/10637 Signed-off-by: Gert Doering (cherry picked from commit 756602e7da11362f25be04743cd09f798b6f528a) --- diff --git a/src/openvpn/crypto_openssl.c b/src/openvpn/crypto_openssl.c index 348bdeec7..4e195ce59 100644 --- a/src/openvpn/crypto_openssl.c +++ b/src/openvpn/crypto_openssl.c @@ -378,7 +378,12 @@ show_available_engines () int rand_bytes(uint8_t *output, int len) { - return RAND_bytes (output, len); + if (unlikely(1 != RAND_bytes (output, len))) + { + msg(D_CRYPT_ERRORS, "RAND_bytes() failed"); + return 0; + } + return 1; } /*