From c23e497da7815bf6ef84461f92339442d3702eda Mon Sep 17 00:00:00 2001 From: Fraser Tweedale Date: Sat, 27 Oct 2018 12:11:41 +0800 Subject: [PATCH] Support GeneralSubtrees with minimum = 0 The Name Constraints extension contains GeneralSubtree values indicating included or excluded subtrees. It is defined as: GeneralSubtree ::= SEQUENCE { base GeneralName, minimum [0] BaseDistance DEFAULT 0, maximum [1] BaseDistance OPTIONAL } RFC 5280 further specifies: Within this profile, the minimum and maximum fields are not used with any name forms, thus, the minimum MUST be zero, and maximum MUST be absent. Because the minimum fields has DEFAULT 0, and certificates should be encoded using DER, the situation where minimum = 0 occurs in a certificate should not arise. Nevertheless, it does arise. For example, I have seen certificates issued by Microsoft programs that contain GeneralSubtree values encoded thus. Enhance the Name Constraints matching routine to handle the case where minimum is specified. If present, it must be zero. The maximum field remains prohibited. Reviewed-by: Paul Yang Reviewed-by: Paul Dale (Merged from https://github.com/openssl/openssl/pull/7039) --- crypto/x509v3/v3_ncons.c | 26 ++++++++++++++++++++++++-- 1 file changed, 24 insertions(+), 2 deletions(-) diff --git a/crypto/x509v3/v3_ncons.c b/crypto/x509v3/v3_ncons.c index 9a2cd5af00..8465818f90 100644 --- a/crypto/x509v3/v3_ncons.c +++ b/crypto/x509v3/v3_ncons.c @@ -14,6 +14,7 @@ #include #include #include +#include #include "internal/x509_int.h" #include "ext_dat.h" @@ -435,6 +436,27 @@ int NAME_CONSTRAINTS_check_CN(X509 *x, NAME_CONSTRAINTS *nc) return X509_V_OK; } +/* + * Return nonzero if the GeneralSubtree has valid 'minimum' field + * (must be absent or 0) and valid 'maximum' field (must be absent). + */ +static int nc_minmax_valid(GENERAL_SUBTREE *sub) { + BIGNUM *bn = NULL; + int ok = 1; + + if (sub->maximum) + ok = 0; + + if (sub->minimum) { + bn = ASN1_INTEGER_to_BN(sub->minimum, NULL); + if (bn == NULL || !BN_is_zero(bn)) + ok = 0; + BN_free(bn); + } + + return ok; +} + static int nc_match(GENERAL_NAME *gen, NAME_CONSTRAINTS *nc) { GENERAL_SUBTREE *sub; @@ -449,7 +471,7 @@ static int nc_match(GENERAL_NAME *gen, NAME_CONSTRAINTS *nc) sub = sk_GENERAL_SUBTREE_value(nc->permittedSubtrees, i); if (gen->type != sub->base->type) continue; - if (sub->minimum || sub->maximum) + if (!nc_minmax_valid(sub)) return X509_V_ERR_SUBTREE_MINMAX; /* If we already have a match don't bother trying any more */ if (match == 2) @@ -472,7 +494,7 @@ static int nc_match(GENERAL_NAME *gen, NAME_CONSTRAINTS *nc) sub = sk_GENERAL_SUBTREE_value(nc->excludedSubtrees, i); if (gen->type != sub->base->type) continue; - if (sub->minimum || sub->maximum) + if (!nc_minmax_valid(sub)) return X509_V_ERR_SUBTREE_MINMAX; r = nc_match_single(gen, sub->base); -- 2.25.1