handle MS PACs that lack server checksum

target_version 1.9
tags: pullup

Apple Mac OS X Server's Open Directory KDC issues MS PAC like
authorization data that lacks a server checksum.  If this checksum is
missing, mark the PAC as unverfied, but allow
krb5int_authdata_verify() to succeed.  Filter out the unverified PAC
in subsequent calls to krb5_authdata_get_attribute().  Add trace
points to indicate where this behavior occurs.

Thanks to Helmut Grohne for help with analysis.  This bug is also
Debian Bug #604925:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=604925

This change should also get backported to krb5-1.8.x.

ticket: 6839

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@24564 dc483132-0cff-0310-8789-dd5450dbe970

2 files changed, 32 insertions, 1 deletions

diff --git a/src/include/k5-trace.h b/src/include/k5-trace.h
index 3efe0e401..1bd4b4451 100644
--- a/src/include/k5-trace.h
+++ b/src/include/k5-trace.h
@@ -194,6 +194,12 @@
     TRACE(c, (c, "Negotiating for enctypes in authenticator: {etypes}", \
               etypes))
 
+#define TRACE_MSPAC_NOSRVCKSUM(c) \
+    TRACE(c, (c, "MS PAC lacks a server checksum.  "\
+              "Apple Open Directory bug?"))
+#define TRACE_MSPAC_DISCARD_UNVERF(c) \
+    TRACE(c, (c, "Filtering out unverified MS PAC"))
+
 #define TRACE_PREAUTH_COOKIE(c, len, data) \
     TRACE(c, (c, "Received cookie: {lenstr}", (size_t) len, data))
 #define TRACE_PREAUTH_ENC_TS_KEY_GAK(c, keyblock) \
diff --git a/src/lib/krb5/krb/pac.c b/src/lib/krb5/krb/pac.c
index 983b4e8a5..47b3a3b91 100644
--- a/src/lib/krb5/krb/pac.c
+++ b/src/lib/krb5/krb/pac.c
@@ -637,8 +637,17 @@ krb5_pac_verify(krb5_context context,
         return EINVAL;
 
     ret = k5_pac_verify_server_checksum(context, pac, server);
-    if (ret != 0)
+    if (ret == ENOENT) {
+        /*
+         * Apple Mac OS X Server Open Directory KDC (at least 10.6)
+         * appears to provide a PAC that lacks a server checksum.
+         */
+        TRACE_MSPAC_NOSRVCKSUM(context);
+        pac->verified = FALSE;
+        return ret;
+    } else if (ret != 0) {
         return ret;
+    }
 
     if (privsvr != NULL) {
         ret = k5_pac_verify_kdc_checksum(context, pac, privsvr);
@@ -802,6 +811,16 @@ mspac_verify(krb5_context kcontext,
                            key,
                            NULL);
 
+    /*
+     * If the server checksum is not found, return success to
+     * krb5int_authdata_verify() to work around an apparent Open
+     * Directory bug.  Non-verified PACs won't be returned by
+     * mspac_get_attribute().
+     */
+    if (code == ENOENT && !pacctx->pac->verified) {
+        code = 0;
+    }
+
 #if 0
     /*
      * Now, we could return 0 and just set pac->verified to FALSE.
@@ -977,6 +996,12 @@ mspac_get_attribute(krb5_context kcontext,
     if (*more != -1 || pacctx->pac == NULL)
         return ENOENT;
 
+    /* If it didn't verify, pretend it didn't exist. */
+    if (!pacctx->pac->verified) {
+        TRACE_MSPAC_DISCARD_UNVERF(kcontext);
+        return ENOENT;
+    }
+
     code = mspac_attr2type(attribute, &type);
     if (code != 0)
         return code;