Simplify purpose checks
The check_ca calls are purpose-independent and redundant. Extract them
to common code. This makes it clearer that the purpose checks (almost)
all have the exact same structure.
Change-Id: I16218da1d994f59afc730424e9ad63f28cae14db
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/65210
Reviewed-by: Bob Beck <bbe@google.com>
Auto-Submit: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
diff --git a/crypto/x509/v3_purp.c b/crypto/x509/v3_purp.c
index 2985dce..5419f06 100644
--- a/crypto/x509/v3_purp.c
+++ b/crypto/x509/v3_purp.c
@@ -74,13 +74,13 @@
#define xku_reject(x, usage) \
(((x)->ex_flags & EXFLAG_XKUSAGE) && !((x)->ex_xkusage & (usage)))
+static int check_ca(const X509 *x);
static int check_purpose_ssl_client(const X509_PURPOSE *xp, const X509 *x,
int ca);
static int check_purpose_ssl_server(const X509_PURPOSE *xp, const X509 *x,
int ca);
static int check_purpose_ns_ssl_server(const X509_PURPOSE *xp, const X509 *x,
int ca);
-static int purpose_smime(const X509 *x, int ca);
static int check_purpose_smime_sign(const X509_PURPOSE *xp, const X509 *x,
int ca);
static int check_purpose_smime_encrypt(const X509_PURPOSE *xp, const X509 *x,
@@ -90,7 +90,6 @@
static int check_purpose_timestamp_sign(const X509_PURPOSE *xp, const X509 *x,
int ca);
static int no_check(const X509_PURPOSE *xp, const X509 *x, int ca);
-static int ocsp_helper(const X509_PURPOSE *xp, const X509 *x, int ca);
static const X509_PURPOSE xstandard[] = {
{X509_PURPOSE_SSL_CLIENT, X509_TRUST_SSL_CLIENT, 0,
@@ -109,7 +108,9 @@
(char *)"CRL signing", (char *)"crlsign", NULL},
{X509_PURPOSE_ANY, X509_TRUST_DEFAULT, 0, no_check, (char *)"Any Purpose",
(char *)"any", NULL},
- {X509_PURPOSE_OCSP_HELPER, X509_TRUST_COMPAT, 0, ocsp_helper,
+ // |X509_PURPOSE_OCSP_HELPER| performs no actual checks. OpenSSL's OCSP
+ // implementation relied on the caller performing EKU and KU checks.
+ {X509_PURPOSE_OCSP_HELPER, X509_TRUST_COMPAT, 0, no_check,
(char *)"OCSP helper", (char *)"ocsphelper", NULL},
{X509_PURPOSE_TIMESTAMP_SIGN, X509_TRUST_TSA, 0,
check_purpose_timestamp_sign, (char *)"Time Stamp signing",
@@ -130,6 +131,13 @@
if (idx == -1) {
return 0;
}
+ // Historically, |check_purpose| implementations other than |X509_PURPOSE_ANY|
+ // called |check_ca|. This is redundant with the |X509_V_ERR_INVALID_CA|
+ // logic, but |X509_check_purpose| is public API, so we preserve this
+ // behavior.
+ if (ca && id != X509_PURPOSE_ANY && !check_ca(x)) {
+ return 0;
+ }
const X509_PURPOSE *pt = X509_PURPOSE_get0(idx);
return pt->check_purpose(pt, x, ca);
}
@@ -411,23 +419,28 @@
return check_ca(x);
}
+// check_purpose returns one if |x| is a valid part of a certificate path for
+// extended key usage |required_xku| and at least one of key usages in
+// |required_kus|. |ca| indicates whether |x| is a CA or end-entity certificate.
+static int check_purpose(const X509 *x, int ca, int required_xku,
+ int required_kus) {
+ // Check extended key usage on the entire chain.
+ if (required_xku != 0 && xku_reject(x, required_xku)) {
+ return 0;
+ }
+
+ // Check key usages only on the end-entity certificate.
+ return ca || !ku_reject(x, required_kus);
+}
+
static int check_purpose_ssl_client(const X509_PURPOSE *xp, const X509 *x,
int ca) {
- if (xku_reject(x, XKU_SSL_CLIENT)) {
- return 0;
- }
- if (ca) {
- // TODO(davidben): Move the various |check_ca| calls out of the
- // |check_purpose| callbacks. Those checks are purpose-independent. They are
- // also redundant when called from |X509_verify_cert|, though
- // not when |X509_check_purpose| is called directly.
- return check_ca(x);
- }
- // We need to do digital signatures or key agreement
- if (ku_reject(x, X509v3_KU_DIGITAL_SIGNATURE | X509v3_KU_KEY_AGREEMENT)) {
- return 0;
- }
- return 1;
+ // We need to do digital signatures or key agreement.
+ //
+ // TODO(davidben): We do not implement any TLS client certificate modes based
+ // on key agreement.
+ return check_purpose(x, ca, XKU_SSL_CLIENT,
+ X509v3_KU_DIGITAL_SIGNATURE | X509v3_KU_KEY_AGREEMENT);
}
// Key usage needed for TLS/SSL server: digital signature, encipherment or
@@ -439,96 +452,35 @@
static int check_purpose_ssl_server(const X509_PURPOSE *xp, const X509 *x,
int ca) {
- if (xku_reject(x, XKU_SSL_SERVER)) {
- return 0;
- }
- if (ca) {
- return check_ca(x);
- }
-
- if (ku_reject(x, X509v3_KU_TLS)) {
- return 0;
- }
-
- return 1;
+ return check_purpose(x, ca, XKU_SSL_SERVER, X509v3_KU_TLS);
}
static int check_purpose_ns_ssl_server(const X509_PURPOSE *xp, const X509 *x,
int ca) {
- int ret = check_purpose_ssl_server(xp, x, ca);
- if (!ret || ca) {
- return ret;
- }
- // We need to encipher or Netscape complains
- if (ku_reject(x, X509v3_KU_KEY_ENCIPHERMENT)) {
- return 0;
- }
- return ret;
-}
-
-// purpose_smime returns one if |x| is a valid S/MIME leaf (|ca| is zero) or CA
-// (|ca| is one) certificate, and zero otherwise.
-static int purpose_smime(const X509 *x, int ca) {
- if (xku_reject(x, XKU_SMIME)) {
- return 0;
- }
- if (ca) {
- return check_ca(x);
- }
- return 1;
+ // We need to encipher or Netscape complains.
+ return check_purpose(x, ca, XKU_SSL_SERVER, X509v3_KU_KEY_ENCIPHERMENT);
}
static int check_purpose_smime_sign(const X509_PURPOSE *xp, const X509 *x,
int ca) {
- int ret = purpose_smime(x, ca);
- if (!ret || ca) {
- return ret;
- }
- if (ku_reject(x, X509v3_KU_DIGITAL_SIGNATURE | X509v3_KU_NON_REPUDIATION)) {
- return 0;
- }
- return ret;
+ return check_purpose(x, ca, XKU_SMIME,
+ X509v3_KU_DIGITAL_SIGNATURE | X509v3_KU_NON_REPUDIATION);
}
static int check_purpose_smime_encrypt(const X509_PURPOSE *xp, const X509 *x,
int ca) {
- int ret = purpose_smime(x, ca);
- if (!ret || ca) {
- return ret;
- }
- if (ku_reject(x, X509v3_KU_KEY_ENCIPHERMENT)) {
- return 0;
- }
- return ret;
+ return check_purpose(x, ca, XKU_SMIME, X509v3_KU_KEY_ENCIPHERMENT);
}
static int check_purpose_crl_sign(const X509_PURPOSE *xp, const X509 *x,
int ca) {
- if (ca) {
- return check_ca(x);
- }
- if (ku_reject(x, X509v3_KU_CRL_SIGN)) {
- return 0;
- }
- return 1;
-}
-
-// OCSP helper: this is *not* a full OCSP check. It just checks that each CA
-// is valid. Additional checks must be made on the chain.
-
-static int ocsp_helper(const X509_PURPOSE *xp, const X509 *x, int ca) {
- if (ca) {
- return check_ca(x);
- }
- // leaf certificate is checked in OCSP_verify()
- return 1;
+ return check_purpose(x, ca, /*required_xku=*/0, X509v3_KU_CRL_SIGN);
}
static int check_purpose_timestamp_sign(const X509_PURPOSE *xp, const X509 *x,
int ca) {
- // If ca is true we must return if this is a valid CA certificate.
if (ca) {
- return check_ca(x);
+ return 1;
}
// Check the optional key usage field:
@@ -544,6 +496,8 @@
}
// Only time stamp key usage is permitted and it's required.
+ //
+ // TODO(davidben): Should we check EKUs up the chain like the other cases?
if (!(x->ex_flags & EXFLAG_XKUSAGE) || x->ex_xkusage != XKU_TIMESTAMP) {
return 0;
}
