krb5: Fix S4U2Self KDC crash when anon is restricted

This is CVE-2016-3120

The validate_as_request function in kdc_util.c in the Key Distribution
Center (KDC) in MIT Kerberos 5 (aka krb5) before 1.13.6 and 1.4.x before
1.14.3, when restrict_anonymous_to_tgt is enabled, uses an incorrect
client data structure, which allows remote authenticated users to cause
a denial of service (NULL pointer dereference and daemon crash) via an
S4U2Self request.

Signed-off-by: Alexandru Moise <alexandru.moise@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>

2 files changed, 64 insertions, 0 deletions

diff --git a/meta-oe/recipes-connectivity/krb5/krb5/krb5-CVE-2016-3120.patch b/meta-oe/recipes-connectivity/krb5/krb5/krb5-CVE-2016-3120.patch
new file mode 100644
index 000000000..dbc46bb79
--- /dev/null
+++ b/meta-oe/recipes-connectivity/krb5/krb5/krb5-CVE-2016-3120.patch
@@ -0,0 +1,63 @@
+From 5b9b82d0696f1ffd4e693c1f8eafc0915b15e85b Mon Sep 17 00:00:00 2001
+From: Greg Hudson <ghudson@mit.edu>
+Date: Tue, 19 Jul 2016 11:00:28 -0400
+Subject: [PATCH] Fix S4U2Self KDC crash when anon is restricted
+
+cherry-picked from 93b4a6306a0026cf1cc31ac4bd8a49ba5d034ba7 upstream
+
+In validate_as_request(), when enforcing restrict_anonymous_to_tgt,
+use client.princ instead of request->client; the latter is NULL when
+validating S4U2Self requests.
+
+CVE-2016-3120:
+
+In MIT krb5 1.9 and later, an authenticated attacker can cause krb5kdc
+to dereference a null pointer if the restrict_anonymous_to_tgt option
+is set to true, by making an S4U2Self request.
+
+  CVSSv2 Vector: AV:N/AC:H/Au:S/C:N/I:N/A:C/E:H/RL:OF/RC:C
+
+ticket: 8458 (new)
+target_version: 1.14-next
+target_version: 1.13-next
+
+Upstream-Status: Backport
+
+Signed-off-by: Alexandru Moise <alexandru.moise@windriver.com>
+---
+ src/kdc/kdc_util.c    | 2 +-
+ src/tests/t_pkinit.py | 5 +++++
+ 2 files changed, 6 insertions(+), 1 deletion(-)
+
+diff --git a/src/kdc/kdc_util.c b/src/kdc/kdc_util.c
+index 48be1ae..10daec4 100644
+--- a/src/kdc/kdc_util.c
++++ b/src/kdc/kdc_util.c
+@@ -700,7 +700,7 @@ validate_as_request(kdc_realm_t *kdc_active_realm,
+         return(KDC_ERR_MUST_USE_USER2USER);
+     }
+ 
+-    if (check_anon(kdc_active_realm, request->client, request->server) != 0) {
++    if (check_anon(kdc_active_realm, client.princ, request->server) != 0) {
+         *status = "ANONYMOUS NOT ALLOWED";
+         return(KDC_ERR_POLICY);
+     }
+diff --git a/src/tests/t_pkinit.py b/src/tests/t_pkinit.py
+index 762e322..d27d05b 100644
+--- a/src/tests/t_pkinit.py
++++ b/src/tests/t_pkinit.py
+@@ -94,6 +94,11 @@ out = realm.run([kvno, realm.host_princ], expected_code=1)
+ if 'KDC policy rejects request' not in out:
+     fail('Wrong error for restricted anonymous PKINIT')
+ 
++# Regression test for #8458: S4U2Self requests crash the KDC if
++# anonymous is restricted.
++realm.kinit(realm.host_princ, flags=['-k'])
++realm.run([kvno, '-U', 'user', realm.host_princ])
++
+ # Go back to a normal KDC and disable anonymous PKINIT.
+ realm.stop_kdc()
+ realm.start_kdc()
+-- 
+2.5.0
+
diff --git a/meta-oe/recipes-connectivity/krb5/krb5_1.13.2.bb b/meta-oe/recipes-connectivity/krb5/krb5_1.13.2.bb
index 3a3886bce..12d35319c 100644
--- a/meta-oe/recipes-connectivity/krb5/krb5_1.13.2.bb
+++ b/meta-oe/recipes-connectivity/krb5/krb5_1.13.2.bb
@@ -36,6 +36,7 @@ SRC_URI = "http://web.mit.edu/kerberos/dist/${BPN}/${SHRT_VER}/${BP}-signed.tar
            file://krb5-admin-server.service \
            file://krb5-CVE-2016-3119.patch;striplevel=2 \
            file://0001-Work-around-uninitialized-warning-in-cc_kcm.c.patch;striplevel=2 \
+           file://krb5-CVE-2016-3120.patch;striplevel=2 \
 "
 SRC_URI[md5sum] = "f7ebfa6c99c10b16979ebf9a98343189"
 SRC_URI[sha256sum] = "e528c30b0209c741f6f320cb83122ded92f291802b6a1a1dc1a01dcdb3ff6de1"