- djm@cvs.openbsd.org 2010/05/07 11:30:30

     [auth-options.c auth-options.h auth.c auth.h auth2-pubkey.c]
     [key.c servconf.c servconf.h sshd.8 sshd_config.5]
     add some optional indirection to matching of principal names listed
     in certificates. Currently, a certificate must include the a user's name
     to be accepted for authentication. This change adds the ability to
     specify a list of certificate principal names that are acceptable.

     When authenticating using a CA trusted through ~/.ssh/authorized_keys,
     this adds a new principals="name1[,name2,...]" key option.

     For CAs listed through sshd_config's TrustedCAKeys option, a new config
     option "AuthorizedPrincipalsFile" specifies a per-user file containing
     the list of acceptable names.

     If either option is absent, the current behaviour of requiring the
     username to appear in principals continues to apply.

     These options are useful for role accounts, disjoint account namespaces
     and "user@realm"-style naming policies in certificates.

     feedback and ok markus@

1 files changed, 94 insertions, 8 deletions

diff --git a/auth2-pubkey.c b/auth2-pubkey.c
index 83ecd6590..6b4a99725 100644
--- a/auth2-pubkey.c
+++ b/auth2-pubkey.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-pubkey.c,v 1.23 2010/04/16 01:47:26 djm Exp $ */
+/* $OpenBSD: auth2-pubkey.c,v 1.24 2010/05/07 11:30:29 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -57,6 +57,7 @@
 #include "monitor_wrap.h"
 #include "misc.h"
 #include "authfile.h"
+#include "match.h"
 
 /* import */
 extern ServerOptions options;
@@ -176,6 +177,63 @@ done:
         return authenticated;
 }
 
+static int
+match_principals_option(const char *principal_list, struct KeyCert *cert)
+{
+        char *result;
+        u_int i;
+
+        /* XXX percent_expand() sequences for authorized_principals? */
+
+        for (i = 0; i < cert->nprincipals; i++) {
+                if ((result = match_list(cert->principals[i],
+                    principal_list, NULL)) != NULL) {
+                        debug3("matched principal from key options \"%.100s\"",
+                            result);
+                        xfree(result);
+                        return 1;
+                }
+        }
+        return 0;
+}
+
+static int
+match_principals_file(const char *file, struct passwd *pw, struct KeyCert *cert)
+{
+        FILE *f;
+        char line[SSH_MAX_PUBKEY_BYTES], *cp;
+        u_long linenum = 0;
+        u_int i;
+
+        temporarily_use_uid(pw);
+        debug("trying authorized principals file %s", file);
+        if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
+                restore_uid();
+                return 0;
+        }
+        while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
+                /* Skip leading whitespace, empty and comment lines. */
+                for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
+                        ;
+                if (!*cp || *cp == '\n' || *cp == '#')
+                        continue;
+                line[strcspn(line, "\n")] = '\0';
+
+                for (i = 0; i < cert->nprincipals; i++) {
+                        if (strcmp(cp, cert->principals[i]) == 0) {
+                                debug3("matched principal from file \"%.100s\"",
+                                    cert->principals[i]);
+                                fclose(f);
+                                restore_uid();
+                                return 1;
+                        }
+                }
+        }
+        fclose(f);
+        restore_uid();
+        return 0;
+}       
+
 /* return 1 if user allows given key */
 static int
 user_key_allowed2(struct passwd *pw, Key *key, char *file)
@@ -244,13 +302,26 @@ user_key_allowed2(struct passwd *pw, Key *key, char *file)
                             SSH_FP_HEX);
                         debug("matching CA found: file %s, line %lu, %s %s",
                             file, linenum, key_type(found), fp);
-                        if (key_cert_check_authority(key, 0, 0, pw->pw_name,
-                            &reason) != 0) {
+                        /*
+                         * If the user has specified a list of principals as
+                         * a key option, then prefer that list to matching
+                         * their username in the certificate principals list.
+                         */
+                        if (authorized_principals != NULL &&
+                            !match_principals_option(authorized_principals,
+                            key->cert)) {
+                                reason = "Certificate does not contain an "
+                                    "authorized principal";
+ fail_reason:
                                 xfree(fp);
                                 error("%s", reason);
                                 auth_debug_add("%s", reason);
                                 continue;
                         }
+                        if (key_cert_check_authority(key, 0, 0,
+                            authorized_principals == NULL ? pw->pw_name : NULL,
+                            &reason) != 0)
+                                goto fail_reason;
                         if (auth_cert_options(key, pw) != 0) {
                                 xfree(fp);
                                 continue;
@@ -284,7 +355,7 @@ user_key_allowed2(struct passwd *pw, Key *key, char *file)
 static int
 user_cert_trusted_ca(struct passwd *pw, Key *key)
 {
-        char *ca_fp;
+        char *ca_fp, *principals_file = NULL;
         const char *reason;
         int ret = 0;
 
@@ -301,11 +372,24 @@ user_cert_trusted_ca(struct passwd *pw, Key *key)
                     options.trusted_user_ca_keys);
                 goto out;
         }
-        if (key_cert_check_authority(key, 0, 1, pw->pw_name, &reason) != 0) {
-                error("%s", reason);
-                auth_debug_add("%s", reason);
-                goto out;
+        /*
+         * If AuthorizedPrincipals is in use, then compare the certificate
+         * principals against the names in that file rather than matching
+         * against the username.
+         */
+        if ((principals_file = authorized_principals_file(pw)) != NULL) {
+                if (!match_principals_file(principals_file, pw, key->cert)) {
+                        reason = "Certificate does not contain an "
+                            "authorized principal";
+ fail_reason:
+                        error("%s", reason);
+                        auth_debug_add("%s", reason);
+                        goto out;
+                }
         }
+        if (key_cert_check_authority(key, 0, 1,
+            principals_file == NULL ? pw->pw_name : NULL, &reason) != 0)
+                goto fail_reason;
         if (auth_cert_options(key, pw) != 0)
                 goto out;
 
@@ -315,6 +399,8 @@ user_cert_trusted_ca(struct passwd *pw, Key *key)
         ret = 1;
 
  out:
+        if (principals_file != NULL)
+                xfree(principals_file);
         if (ca_fp != NULL)
                 xfree(ca_fp);
         return ret;