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.

Origin: other, https://github.com/openssh-gsskex/openssh-gsskex/commits/debian/master
Bug: https://bugzilla.mindrot.org/show_bug.cgi?id=1242
Last-Updated: 2020-02-21

Patch-Name: gssapi.patch

1 files changed, 78 insertions, 7 deletions

diff --git a/gss-serv-krb5.c b/gss-serv-krb5.c
index a151bc1e4..ef9beb67c 100644
--- a/gss-serv-krb5.c
+++ b/gss-serv-krb5.c
@@ -1,7 +1,7 @@
 /* $OpenBSD: gss-serv-krb5.c,v 1.9 2018/07/09 21:37:55 markus Exp $ */
 
 /*
- * Copyright (c) 2001-2003 Simon Wilkinson. All rights reserved.
+ * Copyright (c) 2001-2007 Simon Wilkinson. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -120,8 +120,8 @@ ssh_gssapi_krb5_storecreds(ssh_gssapi_client *client)
         krb5_error_code problem;
         krb5_principal princ;
         OM_uint32 maj_status, min_status;
-        int len;
         const char *errmsg;
+        const char *new_ccname;
 
         if (client->creds == NULL) {
                 debug("No credentials stored");
@@ -180,11 +180,16 @@ ssh_gssapi_krb5_storecreds(ssh_gssapi_client *client)
                 return;
         }
 
-        client->store.filename = xstrdup(krb5_cc_get_name(krb_context, ccache));
+        new_ccname = krb5_cc_get_name(krb_context, ccache);
+
         client->store.envvar = "KRB5CCNAME";
-        len = strlen(client->store.filename) + 6;
-        client->store.envval = xmalloc(len);
-        snprintf(client->store.envval, len, "FILE:%s", client->store.filename);
+#ifdef USE_CCAPI
+        xasprintf(&client->store.envval, "API:%s", new_ccname);
+        client->store.filename = NULL;
+#else
+        xasprintf(&client->store.envval, "FILE:%s", new_ccname);
+        client->store.filename = xstrdup(new_ccname);
+#endif
 
 #ifdef USE_PAM
         if (options.use_pam)
@@ -196,6 +201,71 @@ ssh_gssapi_krb5_storecreds(ssh_gssapi_client *client)
         return;
 }
 
+int
+ssh_gssapi_krb5_updatecreds(ssh_gssapi_ccache *store,
+    ssh_gssapi_client *client)
+{
+        krb5_ccache ccache = NULL;
+        krb5_principal principal = NULL;
+        char *name = NULL;
+        krb5_error_code problem;
+        OM_uint32 maj_status, min_status;
+
+        if ((problem = krb5_cc_resolve(krb_context, store->envval, &ccache))) {
+                logit("krb5_cc_resolve(): %.100s",
+                    krb5_get_err_text(krb_context, problem));
+                return 0;
+        }
+
+        /* Find out who the principal in this cache is */
+        if ((problem = krb5_cc_get_principal(krb_context, ccache,
+            &principal))) {
+                logit("krb5_cc_get_principal(): %.100s",
+                    krb5_get_err_text(krb_context, problem));
+                krb5_cc_close(krb_context, ccache);
+                return 0;
+        }
+
+        if ((problem = krb5_unparse_name(krb_context, principal, &name))) {
+                logit("krb5_unparse_name(): %.100s",
+                    krb5_get_err_text(krb_context, problem));
+                krb5_free_principal(krb_context, principal);
+                krb5_cc_close(krb_context, ccache);
+                return 0;
+        }
+
+
+        if (strcmp(name,client->exportedname.value)!=0) {
+                debug("Name in local credentials cache differs. Not storing");
+                krb5_free_principal(krb_context, principal);
+                krb5_cc_close(krb_context, ccache);
+                krb5_free_unparsed_name(krb_context, name);
+                return 0;
+        }
+        krb5_free_unparsed_name(krb_context, name);
+
+        /* Name matches, so lets get on with it! */
+
+        if ((problem = krb5_cc_initialize(krb_context, ccache, principal))) {
+                logit("krb5_cc_initialize(): %.100s",
+                    krb5_get_err_text(krb_context, problem));
+                krb5_free_principal(krb_context, principal);
+                krb5_cc_close(krb_context, ccache);
+                return 0;
+        }
+
+        krb5_free_principal(krb_context, principal);
+
+        if ((maj_status = gss_krb5_copy_ccache(&min_status, client->creds,
+            ccache))) {
+                logit("gss_krb5_copy_ccache() failed. Sorry!");
+                krb5_cc_close(krb_context, ccache);
+                return 0;
+        }
+
+        return 1;
+}
+
 ssh_gssapi_mech gssapi_kerberos_mech = {
         "toWM5Slw5Ew8Mqkay+al2g==",
         "Kerberos",
@@ -203,7 +273,8 @@ ssh_gssapi_mech gssapi_kerberos_mech = {
         NULL,
         &ssh_gssapi_krb5_userok,
         NULL,
-        &ssh_gssapi_krb5_storecreds
+        &ssh_gssapi_krb5_storecreds,
+        &ssh_gssapi_krb5_updatecreds
 };
 
 #endif /* KRB5 */