GSSAPI key exchange support

This patch has been rejected upstream: "None of the OpenSSH developers are
in favour of adding this, and this situation has not changed for several
years.  This is not a slight on Simon's patch, which is of fine quality, but
just that a) we don't trust GSSAPI implementations that much and b) we don't
like adding new KEX since they are pre-auth attack surface.  This one is
particularly scary, since it requires hooks out to typically root-owned
system resources."

However, quite a lot of people rely on this in Debian, and it's better to
have it merged into the main openssh package rather than having separate
-krb5 packages (as we used to have).  It seems to have a generally good
security history.

Bug: https://bugzilla.mindrot.org/show_bug.cgi?id=1242
Last-Updated: 2016-08-07

Patch-Name: gssapi.patch

1 files changed, 107 insertions, 1 deletions

diff --git a/monitor.c b/monitor.c
index cb57bd066..05bb48a8e 100644
--- a/monitor.c
+++ b/monitor.c
@@ -158,6 +158,8 @@ int mm_answer_gss_setup_ctx(int, Buffer *);
 int mm_answer_gss_accept_ctx(int, Buffer *);
 int mm_answer_gss_userok(int, Buffer *);
 int mm_answer_gss_checkmic(int, Buffer *);
+int mm_answer_gss_sign(int, Buffer *);
+int mm_answer_gss_updatecreds(int, Buffer *);
 #endif
 
 #ifdef SSH_AUDIT_EVENTS
@@ -235,11 +237,18 @@ struct mon_table mon_dispatch_proto20[] = {
     {MONITOR_REQ_GSSSTEP, MON_ISAUTH, mm_answer_gss_accept_ctx},
     {MONITOR_REQ_GSSUSEROK, MON_AUTH, mm_answer_gss_userok},
     {MONITOR_REQ_GSSCHECKMIC, MON_ISAUTH, mm_answer_gss_checkmic},
+    {MONITOR_REQ_GSSSIGN, MON_ONCE, mm_answer_gss_sign},
 #endif
     {0, 0, NULL}
 };
 
 struct mon_table mon_dispatch_postauth20[] = {
+#ifdef GSSAPI
+    {MONITOR_REQ_GSSSETUP, 0, mm_answer_gss_setup_ctx},
+    {MONITOR_REQ_GSSSTEP, 0, mm_answer_gss_accept_ctx},
+    {MONITOR_REQ_GSSSIGN, 0, mm_answer_gss_sign},
+    {MONITOR_REQ_GSSUPCREDS, 0, mm_answer_gss_updatecreds},
+#endif
 #ifdef WITH_OPENSSL
     {MONITOR_REQ_MODULI, 0, mm_answer_moduli},
 #endif
@@ -354,6 +363,10 @@ monitor_child_preauth(Authctxt *_authctxt, struct monitor *pmonitor)
                 /* Permit requests for moduli and signatures */
                 monitor_permit(mon_dispatch, MONITOR_REQ_MODULI, 1);
                 monitor_permit(mon_dispatch, MONITOR_REQ_SIGN, 1);
+#ifdef GSSAPI
+                /* and for the GSSAPI key exchange */
+                monitor_permit(mon_dispatch, MONITOR_REQ_GSSSETUP, 1);
+#endif
         } else {
                 mon_dispatch = mon_dispatch_proto15;
 
@@ -462,6 +475,10 @@ monitor_child_postauth(struct monitor *pmonitor)
                 monitor_permit(mon_dispatch, MONITOR_REQ_MODULI, 1);
                 monitor_permit(mon_dispatch, MONITOR_REQ_SIGN, 1);
                 monitor_permit(mon_dispatch, MONITOR_REQ_TERM, 1);
+#ifdef GSSAPI
+                /* and for the GSSAPI key exchange */
+                monitor_permit(mon_dispatch, MONITOR_REQ_GSSSETUP, 1);
+#endif          
         } else {
                 mon_dispatch = mon_dispatch_postauth15;
                 monitor_permit(mon_dispatch, MONITOR_REQ_TERM, 1);
@@ -1876,6 +1893,13 @@ monitor_apply_keystate(struct monitor *pmonitor)
 # endif
 #endif /* WITH_OPENSSL */
                 kex->kex[KEX_C25519_SHA256] = kexc25519_server;
+#ifdef GSSAPI
+                if (options.gss_keyex) {
+                        kex->kex[KEX_GSS_GRP1_SHA1] = kexgss_server;
+                        kex->kex[KEX_GSS_GRP14_SHA1] = kexgss_server;
+                        kex->kex[KEX_GSS_GEX_SHA1] = kexgss_server;
+                }
+#endif
                 kex->load_host_public_key=&get_hostkey_public_by_type;
                 kex->load_host_private_key=&get_hostkey_private_by_type;
                 kex->host_key_index=&get_hostkey_index;
@@ -1975,6 +1999,9 @@ mm_answer_gss_setup_ctx(int sock, Buffer *m)
         OM_uint32 major;
         u_int len;
 
+        if (!options.gss_authentication && !options.gss_keyex)
+                fatal("In GSSAPI monitor when GSSAPI is disabled");
+
         goid.elements = buffer_get_string(m, &len);
         goid.length = len;
 
@@ -2002,6 +2029,9 @@ mm_answer_gss_accept_ctx(int sock, Buffer *m)
         OM_uint32 flags = 0; /* GSI needs this */
         u_int len;
 
+        if (!options.gss_authentication && !options.gss_keyex)
+                fatal("In GSSAPI monitor when GSSAPI is disabled");
+
         in.value = buffer_get_string(m, &len);
         in.length = len;
         major = ssh_gssapi_accept_ctx(gsscontext, &in, &out, &flags);
@@ -2019,6 +2049,7 @@ mm_answer_gss_accept_ctx(int sock, Buffer *m)
                 monitor_permit(mon_dispatch, MONITOR_REQ_GSSSTEP, 0);
                 monitor_permit(mon_dispatch, MONITOR_REQ_GSSUSEROK, 1);
                 monitor_permit(mon_dispatch, MONITOR_REQ_GSSCHECKMIC, 1);
+                monitor_permit(mon_dispatch, MONITOR_REQ_GSSSIGN, 1);
         }
         return (0);
 }
@@ -2030,6 +2061,9 @@ mm_answer_gss_checkmic(int sock, Buffer *m)
         OM_uint32 ret;
         u_int len;
 
+        if (!options.gss_authentication && !options.gss_keyex)
+                fatal("In GSSAPI monitor when GSSAPI is disabled");
+
         gssbuf.value = buffer_get_string(m, &len);
         gssbuf.length = len;
         mic.value = buffer_get_string(m, &len);
@@ -2056,7 +2090,11 @@ mm_answer_gss_userok(int sock, Buffer *m)
 {
         int authenticated;
 
-        authenticated = authctxt->valid && ssh_gssapi_userok(authctxt->user);
+        if (!options.gss_authentication && !options.gss_keyex)
+                fatal("In GSSAPI monitor when GSSAPI is disabled");
+
+        authenticated = authctxt->valid && 
+            ssh_gssapi_userok(authctxt->user, authctxt->pw);
 
         buffer_clear(m);
         buffer_put_int(m, authenticated);
@@ -2069,5 +2107,73 @@ mm_answer_gss_userok(int sock, Buffer *m)
         /* Monitor loop will terminate if authenticated */
         return (authenticated);
 }
+
+int 
+mm_answer_gss_sign(int socket, Buffer *m)
+{
+        gss_buffer_desc data;
+        gss_buffer_desc hash = GSS_C_EMPTY_BUFFER;
+        OM_uint32 major, minor;
+        u_int len;
+
+        if (!options.gss_authentication && !options.gss_keyex)
+                fatal("In GSSAPI monitor when GSSAPI is disabled");
+
+        data.value = buffer_get_string(m, &len);
+        data.length = len;
+        if (data.length != 20) 
+                fatal("%s: data length incorrect: %d", __func__, 
+                    (int) data.length);
+
+        /* Save the session ID on the first time around */
+        if (session_id2_len == 0) {
+                session_id2_len = data.length;
+                session_id2 = xmalloc(session_id2_len);
+                memcpy(session_id2, data.value, session_id2_len);
+        }
+        major = ssh_gssapi_sign(gsscontext, &data, &hash);
+
+        free(data.value);
+
+        buffer_clear(m);
+        buffer_put_int(m, major);
+        buffer_put_string(m, hash.value, hash.length);
+
+        mm_request_send(socket, MONITOR_ANS_GSSSIGN, m);
+
+        gss_release_buffer(&minor, &hash);
+
+        /* Turn on getpwnam permissions */
+        monitor_permit(mon_dispatch, MONITOR_REQ_PWNAM, 1);
+        
+        /* And credential updating, for when rekeying */
+        monitor_permit(mon_dispatch, MONITOR_REQ_GSSUPCREDS, 1);
+
+        return (0);
+}
+
+int
+mm_answer_gss_updatecreds(int socket, Buffer *m) {
+        ssh_gssapi_ccache store;
+        int ok;
+
+        store.filename = buffer_get_string(m, NULL);
+        store.envvar   = buffer_get_string(m, NULL);
+        store.envval   = buffer_get_string(m, NULL);
+
+        ok = ssh_gssapi_update_creds(&store);
+
+        free(store.filename);
+        free(store.envvar);
+        free(store.envval);
+
+        buffer_clear(m);
+        buffer_put_int(m, ok);
+
+        mm_request_send(socket, MONITOR_ANS_GSSUPCREDS, m);
+
+        return(0);
+}
+
 #endif /* GSSAPI */