From 1e5dfdc840824723dfa142707aca1f0fca4c0056 Mon Sep 17 00:00:00 2001
From: Jaakko Keränen <jaakko.keranen@iki.fi>
Date: Fri, 26 Mar 2021 11:14:57 +0200
Subject: GmCerts: Relaxed domain verification

Allow a certificate for a higher-level domain to be verified against any subdomains, i.e., implicitly assume every certificate uses wildcards.

CA verification is still done separately, and OpenSSL does that strictly as before.
---
 src/gmcerts.c   | 31 ++++++++++++++++++++++++++++++-
 src/gmcerts.h   |  2 ++
 src/gmrequest.c |  2 +-
 3 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/src/gmcerts.c b/src/gmcerts.c
index 6a1ba98c..2cc10a3d 100644
--- a/src/gmcerts.c
+++ b/src/gmcerts.c
@@ -374,6 +374,35 @@ void deinit_GmCerts(iGmCerts *d) {
     delete_Mutex(d->mtx);
 }
 
+static iRangecc stripFirstDomainLabel_(iRangecc domain) {
+    iRangecc label = iNullRange;
+    if (nextSplit_Rangecc(domain, ".", &label) && nextSplit_Rangecc(domain, ".", &label)) {
+        return (iRangecc){ label.start, domain.end };
+    }
+    return iNullRange;
+}
+
+iBool verifyDomain_GmCerts(const iTlsCertificate *cert, iRangecc domain) {
+    if (verifyDomain_TlsCertificate(cert, domain)) {
+        return iTrue;
+    }
+    /* Allow for an implicit wildcard in the domain name. Self-signed TOFU is really only
+       about the public/private key pair; any other details should be considered
+       complementary. */
+    for (iRangecc higherDomain = stripFirstDomainLabel_(domain);
+         !isEmpty_Range(&higherDomain);
+         higherDomain = stripFirstDomainLabel_(higherDomain)) {
+        if (!iStrStrN(higherDomain.start, ".", size_Range(&higherDomain))) {
+            /* Must have two labels at least. */
+            break;
+        }
+        if (verifyDomain_TlsCertificate(cert, higherDomain)) {
+            return iTrue;
+        }
+    }
+    return iFalse;
+}
+
 iBool checkTrust_GmCerts(iGmCerts *d, iRangecc domain, const iTlsCertificate *cert) {
     if (!cert) {
         return iFalse;
@@ -383,7 +412,7 @@ iBool checkTrust_GmCerts(iGmCerts *d, iRangecc domain, const iTlsCertificate *ce
     }
     /* We trust CA verification implicitly. */
     const iBool isAuth = verify_TlsCertificate(cert) == authority_TlsCertificateVerifyStatus;
-    if (!isAuth && !verifyDomain_TlsCertificate(cert, domain)) {
+    if (!isAuth && !verifyDomain_GmCerts(cert, domain)) {
         return iFalse;
     }
     /* TODO: Could call setTrusted_GmCerts() instead of duplicating the trust-setting. */
diff --git a/src/gmcerts.h b/src/gmcerts.h
index a28c050e..a9859845 100644
--- a/src/gmcerts.h
+++ b/src/gmcerts.h
@@ -95,3 +95,5 @@ const iPtrArray *   listIdentities_GmCerts  (const iGmCerts *, iGmCertsIdentityF
 
 void                signIn_GmCerts          (iGmCerts *, iGmIdentity *identity, const iString *url);
 void                signOut_GmCerts         (iGmCerts *, const iString *url);
+
+iBool               verifyDomain_GmCerts    (const iTlsCertificate *cert, iRangecc domain);
diff --git a/src/gmrequest.c b/src/gmrequest.c
index f065f935..c968990c 100644
--- a/src/gmrequest.c
+++ b/src/gmrequest.c
@@ -157,7 +157,7 @@ static void checkServerCertificate_GmRequest_(iGmRequest *d) {
         if (!isExpired_TlsCertificate(cert)) {
             resp->certFlags |= timeVerified_GmCertFlag;
         }
-        if (verifyDomain_TlsCertificate(cert, domain)) {
+        if (verifyDomain_GmCerts(cert, domain)) {
             resp->certFlags |= domainVerified_GmCertFlag;
         }
         if (checkTrust_GmCerts(d->certs, domain, cert)) {
-- 
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