krb5 commit [krb5-1.16]: Fix capaths "." values on client

https://github.com/krb5/krb5/commit/6b7bd5603f09a44ff406ec0fb2bfe95e2752cd82
commit 6b7bd5603f09a44ff406ec0fb2bfe95e2752cd82
Author: Greg Hudson <[email protected]>
Date:   Sat Mar 3 13:44:00 2018 -0500

    Fix capaths "." values on client
    
    Commit b72aef2c1cbcc76f7fba14ddc54a4e66e7a4e66c (ticket 6966)
    introduced k5_client_realm_path() for use on the client in place of
    krb5_walk_realm_tree(), but failed to handle the special case of a
    capaths "." value as is done in the latter function.  Correct that
    omission and add a test case.
    
    (cherry picked from commit f8d0877f848563d07152a0ee191fe82846fdb8f1)
    
    ticket: 8646
    version_fixed: 1.16.1

 src/lib/krb5/krb/walk_rtree.c |    6 ++++++
 src/tests/t_crossrealm.py     |   10 ++++++++++
 2 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/src/lib/krb5/krb/walk_rtree.c b/src/lib/krb5/krb/walk_rtree.c
index 0566a55..f4e8e35 100644
--- a/src/lib/krb5/krb/walk_rtree.c
+++ b/src/lib/krb5/krb/walk_rtree.c
@@ -133,6 +133,12 @@ k5_client_realm_path(krb5_context context, const krb5_data *client,
     if (retval)
         return retval;
 
+    /* A capaths value of "." means no intermediates. */
+    if (capvals != NULL && capvals[0] != NULL && *capvals[0] == '.') {
+        profile_free_list(capvals);
+        capvals = NULL;
+    }
+
     /* Count capaths (if any) and allocate space.  Leave room for the client
      * realm, server realm, and terminator. */
     for (i = 0; capvals != NULL && capvals[i] != NULL; i++);
diff --git a/src/tests/t_crossrealm.py b/src/tests/t_crossrealm.py
index e7ddb05..4d595dc 100755
--- a/src/tests/t_crossrealm.py
+++ b/src/tests/t_crossrealm.py
@@ -109,6 +109,16 @@ test_kvno(r1, r4.host_princ, 'KDC capaths')
 check_klist(r1, (tgt(r1, r1), tgt(r4, r3), r4.host_princ))
 stop(r1, r2, r3, r4)
 
+# A capaths value of '.' should enforce direct cross-realm, with no
+# intermediate.
+capaths = {'capaths': {'A.X': {'B.X': '.'}}}
+r1, r2, r3 = cross_realms(3, xtgts=((0,1), (1,2)),
+                          args=({'realm': 'A.X', 'krb5_conf': capaths},
+                                {'realm': 'X'}, {'realm': 'B.X'}))
+r1.run([kvno, r3.host_princ], expected_code=1,
+       expected_msg='Server krbtgt/[email protected] not found in Kerberos database')
+stop(r1, r2, r3)
+
 # Test transited error.  The KDC for C does not recognize B as an
 # intermediate realm for A->C, so it refuses to issue a service
 # ticket.