- OpenBSD CVS Sync

   - djm@cvs.openbsd.org 2010/02/26 20:29:54
     [PROTOCOL PROTOCOL.agent PROTOCOL.certkeys addrmatch.c auth-options.c]
     [auth-options.h auth.h auth2-pubkey.c authfd.c dns.c dns.h hostfile.c]
     [hostfile.h kex.h kexdhs.c kexgexs.c key.c key.h match.h monitor.c]
     [myproposal.h servconf.c servconf.h ssh-add.c ssh-agent.c ssh-dss.c]
     [ssh-keygen.1 ssh-keygen.c ssh-rsa.c ssh.1 ssh.c ssh2.h sshconnect.c]
     [sshconnect2.c sshd.8 sshd.c sshd_config.5]
     Add support for certificate key types for users and hosts.

     OpenSSH certificate key types are not X.509 certificates, but a much
     simpler format that encodes a public key, identity information and
     some validity constraints and signs it with a CA key. CA keys are
     regular SSH keys. This certificate style avoids the attack surface
     of X.509 certificates and is very easy to deploy.

     Certified host keys allow automatic acceptance of new host keys
     when a CA certificate is marked as sh/known_hosts.
     see VERIFYING HOST KEYS in ssh(1) for details.

     Certified user keys allow authentication of users when the signing
     CA key is marked as trusted in authorized_keys. See "AUTHORIZED_KEYS
     FILE FORMAT" in sshd(8) for details.

     Certificates are minted using ssh-keygen(1), documentation is in
     the "CERTIFICATES" section of that manpage.

     Documentation on the format of certificates is in the file
     PROTOCOL.certkeys

     feedback and ok markus@

1 files changed, 149 insertions, 1 deletions

diff --git a/auth-options.c b/auth-options.c
index ab085c233..396bda62f 100644
--- a/auth-options.c
+++ b/auth-options.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth-options.c,v 1.44 2009/01/22 10:09:16 djm Exp $ */
+/* $OpenBSD: auth-options.c,v 1.45 2010/02/26 20:29:54 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -44,6 +44,7 @@ int no_agent_forwarding_flag = 0;
 int no_x11_forwarding_flag = 0;
 int no_pty_flag = 0;
 int no_user_rc = 0;
+int key_is_cert_authority = 0;
 
 /* "command=" option. */
 char *forced_command = NULL;
@@ -64,6 +65,7 @@ auth_clear_options(void)
         no_pty_flag = 0;
         no_x11_forwarding_flag = 0;
         no_user_rc = 0;
+        key_is_cert_authority = 0;
         while (custom_environment) {
                 struct envstring *ce = custom_environment;
                 custom_environment = ce->next;
@@ -96,6 +98,12 @@ auth_parse_options(struct passwd *pw, char *opts, char *file, u_long linenum)
                 return 1;
 
         while (*opts && *opts != ' ' && *opts != '\t') {
+                cp = "cert-authority";
+                if (strncasecmp(opts, cp, strlen(cp)) == 0) {
+                        key_is_cert_authority = 1;
+                        opts += strlen(cp);
+                        goto next_option;
+                }
                 cp = "no-port-forwarding";
                 if (strncasecmp(opts, cp, strlen(cp)) == 0) {
                         auth_debug_add("Port forwarding disabled.");
@@ -374,3 +382,143 @@ bad_option:
         /* deny access */
         return 0;
 }
+
+/*
+ * Set options from certificate constraints. These supersede user key options
+ * so this must be called after auth_parse_options().
+ */
+int
+auth_cert_constraints(Buffer *c_orig, struct passwd *pw)
+{
+        u_char *name = NULL, *data_blob = NULL;
+        u_int len;
+        Buffer c, data;
+        int ret = -1;
+
+        int cert_no_port_forwarding_flag = 1;
+        int cert_no_agent_forwarding_flag = 1;
+        int cert_no_x11_forwarding_flag = 1;
+        int cert_no_pty_flag = 1;
+        int cert_no_user_rc = 1;
+        char *cert_forced_command = NULL;
+        int cert_source_address_done = 0;
+
+        buffer_init(&data);
+
+        /* Make copy to avoid altering original */
+        buffer_init(&c);
+        buffer_append(&c, buffer_ptr(c_orig), buffer_len(c_orig));
+
+        while (buffer_len(&c) > 0) {
+                if ((name = buffer_get_string_ret(&c, NULL)) == NULL ||
+                    (data_blob = buffer_get_string_ret(&c, &len)) == NULL) {
+                        error("Certificate constraints corrupt");
+                        goto out;
+                }
+                buffer_append(&data, data_blob, len);
+                debug3("found certificate constraint \"%.100s\" len %u",
+                    name, len);
+                if (strcmp(name, "permit-X11-forwarding") == 0)
+                        cert_no_x11_forwarding_flag = 0;
+                else if (strcmp(name, "permit-agent-forwarding") == 0)
+                        cert_no_agent_forwarding_flag = 0;
+                else if (strcmp(name, "permit-port-forwarding") == 0)
+                        cert_no_port_forwarding_flag = 0;
+                else if (strcmp(name, "permit-pty") == 0)
+                        cert_no_pty_flag = 0;
+                else if (strcmp(name, "permit-user-rc") == 0)
+                        cert_no_user_rc = 0;
+                else if (strcmp(name, "force-command") == 0) {
+                        char *command = buffer_get_string_ret(&data, NULL);
+
+                        if (command == NULL) {
+                                error("Certificate constraint \"%s\" corrupt",
+                                    name);
+                                goto out;
+                        }
+                        if (cert_forced_command != NULL) {
+                                error("Certificate has multiple "
+                                    "forced-command constraints");
+                                xfree(command);
+                                goto out;
+                        }
+                        cert_forced_command = command;
+                } else if (strcmp(name, "source-address") == 0) {
+                        char *allowed = buffer_get_string_ret(&data, NULL);
+                        const char *remote_ip = get_remote_ipaddr();
+                        
+                        if (allowed == NULL) {
+                                error("Certificate constraint \"%s\" corrupt",
+                                    name);
+                                goto out;
+                        }
+                        if (cert_source_address_done++) {
+                                error("Certificate has multiple "
+                                    "source-address constraints");
+                                xfree(allowed);
+                                goto out;
+                        }
+                        switch (addr_match_cidr_list(remote_ip, allowed)) {
+                        case 1:
+                                /* accepted */
+                                xfree(allowed);
+                                break;
+                        case 0:
+                                /* no match */
+                                logit("Authentication tried for %.100s with "
+                                    "valid certificate but not from a "
+                                    "permitted host (ip=%.200s).",
+                                    pw->pw_name, remote_ip);
+                                auth_debug_add("Your address '%.200s' is not "
+                                    "permitted to use this certificate for "
+                                    "login.", remote_ip);
+                                xfree(allowed);
+                                goto out;
+                        case -1:
+                                error("Certificate source-address contents "
+                                    "invalid");
+                                xfree(allowed);
+                                goto out;
+                        }
+                } else {
+                        error("Certificate constraint \"%s\" is not supported",
+                            name);
+                        goto out;
+                }
+
+                if (buffer_len(&data) != 0) {
+                        error("Certificate constraint \"%s\" corrupt "
+                            "(extra data)", name);
+                        goto out;
+                }
+                buffer_clear(&data);
+                xfree(name);
+                xfree(data_blob);
+                name = data_blob = NULL;
+        }
+
+        /* successfully parsed all constraints */
+        ret = 0;
+
+        no_port_forwarding_flag |= cert_no_port_forwarding_flag;
+        no_agent_forwarding_flag |= cert_no_agent_forwarding_flag;
+        no_x11_forwarding_flag |= cert_no_x11_forwarding_flag;
+        no_pty_flag |= cert_no_pty_flag;
+        no_user_rc |= cert_no_user_rc;
+        /* CA-specified forced command supersedes key option */
+        if (cert_forced_command != NULL) {
+                if (forced_command != NULL)
+                        xfree(forced_command);
+                forced_command = cert_forced_command;
+        }
+        
+ out:
+        if (name != NULL)
+                xfree(name);
+        if (data_blob != NULL)
+                xfree(data_blob);
+        buffer_free(&data);
+        buffer_free(&c);
+        return ret;
+}
+