x509_purp: fix doc comment for check_ca()

This comment has gotten out of sync with reality. The "I don't know..."
fallback was removed and a special case for netscape CAs was added.
Sync from the manual and add some more details.

Pointed out by Maximilian Radoy in
https://github.com/libressl/portable/issues/1274

ok kenjiro

1 files changed, 7 insertions, 3 deletions

diff --git a/src/lib/libcrypto/x509/x509_purp.c b/src/lib/libcrypto/x509/x509_purp.c
index 36dfe6abee..ff6d272d39 100644
--- a/src/lib/libcrypto/x509/x509_purp.c
+++ b/src/lib/libcrypto/x509/x509_purp.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: x509_purp.c,v 1.44 2025/05/10 05:54:39 tb Exp $ */
+/* $OpenBSD: x509_purp.c,v 1.45 2026/05/08 04:28:28 tb Exp $ */
 /* Written by Dr Stephen N Henson (steve@openssl.org) for the OpenSSL
  * project 2001.
  */
@@ -580,13 +580,17 @@ x509v3_cache_extensions(X509 *x)
         return (x->ex_flags & EXFLAG_INVALID) == 0;
 }
 
-/* CA checks common to all purposes
+/*
+ * CA checks common to all purposes
  * return codes:
  * 0 not a CA
- * 1 is a CA
+ * 1 is a CA per RFC 5280.
  * 2 basicConstraints absent so "maybe" a CA
+ *   "I don't know..." fallback removed in 2004 (OpenSSL commit 8f284faa)
  * 3 basicConstraints absent but self signed V1.
  * 4 basicConstraints absent but keyUsage present and keyCertSign asserted.
+ * 5 basicConstraints absent but outdated Netscape Certificate Type extension
+ *   indicates that it is a CA certificate
  */
 
 static int