Allow certificates with Basic Constraints CA:false, pathlen:0

Do not mark such certificates with EXFLAG_INVALID although they
violate the RFC 5280, they are syntactically correct and
openssl itself can produce such certificates without any errors
with command such as:

openssl x509 -req -signkey private.pem -in csr.pem -out cert.pem \
  -extfile <(echo "basicConstraints=CA:FALSE,pathlen:0")

With the commit ba4356ae4002a04e28642da60c551877eea804f7 the
EXFLAG_INVALID causes openssl to not consider such certificate
even as leaf self-signed certificate which is breaking existing
installations.

Fixes: #11456

Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11463)

(cherry picked from commit 428cf5ff83a48d0b51c97476586b2cbd053b6302)

diff --git a/crypto/x509v3/v3_purp.c b/crypto/x509v3/v3_purp.c
index 2bc8253d2dab3a69f8f8b59461a0909dfc651296..2eaad1a763cef0b1d9de9331782d7e577d7fa68f 100644 (file)
--- a/crypto/x509v3/v3_purp.c
+++ b/crypto/x509v3/v3_purp.c
@@ -384,12 +384,16 @@ static void x509v3_cache_extensions(X509 *x)
         if (bs->ca)
             x->ex_flags |= EXFLAG_CA;
         if (bs->pathlen) {
-            if ((bs->pathlen->type == V_ASN1_NEG_INTEGER)
-                || !bs->ca) {
+            if (bs->pathlen->type == V_ASN1_NEG_INTEGER) {
                 x->ex_flags |= EXFLAG_INVALID;
                 x->ex_pathlen = 0;
-            } else
+            } else {
                 x->ex_pathlen = ASN1_INTEGER_get(bs->pathlen);
+                if (!bs->ca && x->ex_pathlen != 0) {
+                    x->ex_flags |= EXFLAG_INVALID;
+                    x->ex_pathlen = 0;
+                }
+            }
         } else
             x->ex_pathlen = -1;
         BASIC_CONSTRAINTS_free(bs);