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strongswan: add fix for CVE-2022-40617
Full details of the CVE can be found at the following link: https://www.strongswan.org/blog/2022/10/03/strongswan-vulnerability-(cve-2022-40617).html Signed-off-by: Florian Eckert <fe@dev.tdt.de>
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Florian Eckert
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From 66d3b2e0e596a6eac1ebcd15c83a8d9368fe7b34 Mon Sep 17 00:00:00 2001
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From: Tobias Brunner <tobias@strongswan.org>
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Date: Fri, 22 Jul 2022 15:37:43 +0200
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Subject: [PATCH] credential-manager: Do online revocation checks only after
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basic trust chain validation
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This avoids querying URLs of potentially untrusted certificates, e.g. if
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an attacker sends a specially crafted end-entity and intermediate CA
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certificate with a CDP that points to a server that completes the
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TCP handshake but then does not send any further data, which will block
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the fetcher thread (depending on the plugin) for as long as the default
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timeout for TCP. Doing that multiple times will block all worker threads,
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leading to a DoS attack.
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The logging during the certificate verification obviously changes. The
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following example shows the output of `pki --verify` for the current
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strongswan.org certificate:
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new:
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using certificate "CN=www.strongswan.org"
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using trusted intermediate ca certificate "C=US, O=Let's Encrypt, CN=R3"
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using trusted ca certificate "C=US, O=Internet Security Research Group, CN=ISRG Root X1"
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reached self-signed root ca with a path length of 1
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checking certificate status of "CN=www.strongswan.org"
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requesting ocsp status from 'http://r3.o.lencr.org' ...
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ocsp response correctly signed by "C=US, O=Let's Encrypt, CN=R3"
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ocsp response is valid: until Jul 27 12:59:58 2022
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certificate status is good
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checking certificate status of "C=US, O=Let's Encrypt, CN=R3"
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ocsp response verification failed, no signer certificate 'C=US, O=Let's Encrypt, CN=R3' found
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fetching crl from 'http://x1.c.lencr.org/' ...
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using trusted certificate "C=US, O=Internet Security Research Group, CN=ISRG Root X1"
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crl correctly signed by "C=US, O=Internet Security Research Group, CN=ISRG Root X1"
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crl is valid: until Apr 18 01:59:59 2023
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certificate status is good
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certificate trusted, lifetimes valid, certificate not revoked
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old:
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using certificate "CN=www.strongswan.org"
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using trusted intermediate ca certificate "C=US, O=Let's Encrypt, CN=R3"
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checking certificate status of "CN=www.strongswan.org"
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requesting ocsp status from 'http://r3.o.lencr.org' ...
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ocsp response correctly signed by "C=US, O=Let's Encrypt, CN=R3"
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ocsp response is valid: until Jul 27 12:59:58 2022
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certificate status is good
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using trusted ca certificate "C=US, O=Internet Security Research Group, CN=ISRG Root X1"
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checking certificate status of "C=US, O=Let's Encrypt, CN=R3"
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ocsp response verification failed, no signer certificate 'C=US, O=Let's Encrypt, CN=R3' found
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fetching crl from 'http://x1.c.lencr.org/' ...
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using trusted certificate "C=US, O=Internet Security Research Group, CN=ISRG Root X1"
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crl correctly signed by "C=US, O=Internet Security Research Group, CN=ISRG Root X1"
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crl is valid: until Apr 18 01:59:59 2023
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certificate status is good
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reached self-signed root ca with a path length of 1
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certificate trusted, lifetimes valid, certificate not revoked
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Note that this also fixes an issue with the previous dual-use of the
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`trusted` flag. It not only indicated whether the chain is trusted but
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also whether the current issuer is the root anchor (the corresponding
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flag in the `cert_validator_t` interface is called `anchor`). This was
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a problem when building multi-level trust chains for pre-trusted
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end-entity certificates (i.e. where `trusted` is TRUE from the start).
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This caused the main loop to get aborted after the first intermediate CA
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certificate and the mentioned `anchor` flag wasn't correct in any calls
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to `cert_validator_t` implementations.
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Fixes: CVE-2022-40617
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---
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.../credentials/credential_manager.c | 54 +++++++++++++++----
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1 file changed, 45 insertions(+), 9 deletions(-)
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--- a/src/libstrongswan/credentials/credential_manager.c
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+++ b/src/libstrongswan/credentials/credential_manager.c
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@@ -555,7 +555,7 @@ static void cache_queue(private_credenti
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*/
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static bool check_lifetime(private_credential_manager_t *this,
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certificate_t *cert, char *label,
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- int pathlen, bool trusted, auth_cfg_t *auth)
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+ int pathlen, bool anchor, auth_cfg_t *auth)
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{
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time_t not_before, not_after;
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cert_validator_t *validator;
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@@ -570,7 +570,7 @@ static bool check_lifetime(private_crede
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continue;
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}
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status = validator->check_lifetime(validator, cert,
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- pathlen, trusted, auth);
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+ pathlen, anchor, auth);
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if (status != NEED_MORE)
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{
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break;
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@@ -603,13 +603,13 @@ static bool check_lifetime(private_crede
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*/
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static bool check_certificate(private_credential_manager_t *this,
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certificate_t *subject, certificate_t *issuer, bool online,
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- int pathlen, bool trusted, auth_cfg_t *auth)
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+ int pathlen, bool anchor, auth_cfg_t *auth)
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{
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cert_validator_t *validator;
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enumerator_t *enumerator;
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if (!check_lifetime(this, subject, "subject", pathlen, FALSE, auth) ||
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- !check_lifetime(this, issuer, "issuer", pathlen + 1, trusted, auth))
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+ !check_lifetime(this, issuer, "issuer", pathlen + 1, anchor, auth))
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{
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return FALSE;
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}
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@@ -622,7 +622,7 @@ static bool check_certificate(private_cr
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continue;
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}
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if (!validator->validate(validator, subject, issuer,
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- online, pathlen, trusted, auth))
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+ online, pathlen, anchor, auth))
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{
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enumerator->destroy(enumerator);
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return FALSE;
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@@ -725,6 +725,7 @@ static bool verify_trust_chain(private_c
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auth_cfg_t *auth;
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signature_params_t *scheme;
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int pathlen;
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+ bool is_anchor = FALSE;
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auth = auth_cfg_create();
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get_key_strength(subject, auth);
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@@ -742,7 +743,7 @@ static bool verify_trust_chain(private_c
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auth->add(auth, AUTH_RULE_CA_CERT, issuer->get_ref(issuer));
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DBG1(DBG_CFG, " using trusted ca certificate \"%Y\"",
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issuer->get_subject(issuer));
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- trusted = TRUE;
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+ trusted = is_anchor = TRUE;
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}
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else
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{
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@@ -777,11 +778,18 @@ static bool verify_trust_chain(private_c
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DBG1(DBG_CFG, " issuer is \"%Y\"",
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current->get_issuer(current));
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call_hook(this, CRED_HOOK_NO_ISSUER, current);
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+ if (trusted)
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+ {
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+ DBG1(DBG_CFG, " reached end of incomplete trust chain for "
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+ "trusted certificate \"%Y\"",
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+ subject->get_subject(subject));
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+ }
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break;
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}
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}
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- if (!check_certificate(this, current, issuer, online,
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- pathlen, trusted, auth))
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+ /* don't do online verification here */
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+ if (!check_certificate(this, current, issuer, FALSE,
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+ pathlen, is_anchor, auth))
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{
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trusted = FALSE;
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issuer->destroy(issuer);
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@@ -793,7 +801,7 @@ static bool verify_trust_chain(private_c
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}
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current->destroy(current);
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current = issuer;
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- if (trusted)
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+ if (is_anchor)
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{
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DBG1(DBG_CFG, " reached self-signed root ca with a "
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"path length of %d", pathlen);
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@@ -806,6 +814,34 @@ static bool verify_trust_chain(private_c
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DBG1(DBG_CFG, "maximum path length of %d exceeded", MAX_TRUST_PATH_LEN);
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call_hook(this, CRED_HOOK_EXCEEDED_PATH_LEN, subject);
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}
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+ else if (trusted && online)
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+ {
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+ enumerator_t *enumerator;
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+ auth_rule_t rule;
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+
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+ /* do online revocation checks after basic validation of the chain */
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+ pathlen = 0;
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+ current = subject;
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+ enumerator = auth->create_enumerator(auth);
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+ while (enumerator->enumerate(enumerator, &rule, &issuer))
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+ {
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+ if (rule == AUTH_RULE_CA_CERT || rule == AUTH_RULE_IM_CERT)
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+ {
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+ if (!check_certificate(this, current, issuer, TRUE, pathlen++,
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+ rule == AUTH_RULE_CA_CERT, auth))
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+ {
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+ trusted = FALSE;
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+ break;
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+ }
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+ else if (rule == AUTH_RULE_CA_CERT)
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+ {
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+ break;
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+ }
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+ current = issuer;
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+ }
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+ }
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+ enumerator->destroy(enumerator);
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+ }
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if (trusted)
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{
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result->merge(result, auth, FALSE);
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