1 files changed, 346 insertions, 5 deletions

diff --git a/auth.c b/auth.c
index 68a1e4a76..68b9fe795 100644
--- a/auth.c
+++ b/auth.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth.c,v 1.124 2017/09/12 06:32:07 djm Exp $ */
+/* $OpenBSD: auth.c,v 1.127 2018/03/12 00:52:01 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -28,6 +28,7 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/socket.h>
+#include <sys/wait.h>
 
 #include <netinet/in.h>
 
@@ -73,12 +74,14 @@
 #include "authfile.h"
 #include "ssherr.h"
 #include "compat.h"
+#include "channels.h"
 
 /* import */
 extern ServerOptions options;
 extern int use_privsep;
 extern Buffer loginmsg;
 extern struct passwd *privsep_pw;
+extern struct sshauthopt *auth_opts;
 
 /* Debugging messages */
 Buffer auth_debug;
@@ -385,10 +388,8 @@ auth_maxtries_exceeded(Authctxt *authctxt)
  * Check whether root logins are disallowed.
  */
 int
-auth_root_allowed(const char *method)
+auth_root_allowed(struct ssh *ssh, const char *method)
 {
-        struct ssh *ssh = active_state; /* XXX */
-
         switch (options.permit_root_login) {
         case PERMIT_YES:
                 return 1;
@@ -400,7 +401,7 @@ auth_root_allowed(const char *method)
                         return 1;
                 break;
         case PERMIT_FORCED_ONLY:
-                if (forced_command) {
+                if (auth_opts->force_command != NULL) {
                         logit("Root login accepted for forced command.");
                         return 1;
                 }
@@ -747,3 +748,343 @@ auth_get_canonical_hostname(struct ssh *ssh, int use_dns)
                 return dnsname;
         }
 }
+
+/*
+ * Runs command in a subprocess wuth a minimal environment.
+ * Returns pid on success, 0 on failure.
+ * The child stdout and stderr maybe captured, left attached or sent to
+ * /dev/null depending on the contents of flags.
+ * "tag" is prepended to log messages.
+ * NB. "command" is only used for logging; the actual command executed is
+ * av[0].
+ */
+pid_t
+subprocess(const char *tag, struct passwd *pw, const char *command,
+    int ac, char **av, FILE **child, u_int flags)
+{
+        FILE *f = NULL;
+        struct stat st;
+        int fd, devnull, p[2], i;
+        pid_t pid;
+        char *cp, errmsg[512];
+        u_int envsize;
+        char **child_env;
+
+        if (child != NULL)
+                *child = NULL;
+
+        debug3("%s: %s command \"%s\" running as %s (flags 0x%x)", __func__,
+            tag, command, pw->pw_name, flags);
+
+        /* Check consistency */
+        if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0 &&
+            (flags & SSH_SUBPROCESS_STDOUT_CAPTURE) != 0) {
+                error("%s: inconsistent flags", __func__);
+                return 0;
+        }
+        if (((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) == 0) != (child == NULL)) {
+                error("%s: inconsistent flags/output", __func__);
+                return 0;
+        }
+
+        /*
+         * If executing an explicit binary, then verify the it exists
+         * and appears safe-ish to execute
+         */
+        if (*av[0] != '/') {
+                error("%s path is not absolute", tag);
+                return 0;
+        }
+        temporarily_use_uid(pw);
+        if (stat(av[0], &st) < 0) {
+                error("Could not stat %s \"%s\": %s", tag,
+                    av[0], strerror(errno));
+                restore_uid();
+                return 0;
+        }
+        if (safe_path(av[0], &st, NULL, 0, errmsg, sizeof(errmsg)) != 0) {
+                error("Unsafe %s \"%s\": %s", tag, av[0], errmsg);
+                restore_uid();
+                return 0;
+        }
+        /* Prepare to keep the child's stdout if requested */
+        if (pipe(p) != 0) {
+                error("%s: pipe: %s", tag, strerror(errno));
+                restore_uid();
+                return 0;
+        }
+        restore_uid();
+
+        switch ((pid = fork())) {
+        case -1: /* error */
+                error("%s: fork: %s", tag, strerror(errno));
+                close(p[0]);
+                close(p[1]);
+                return 0;
+        case 0: /* child */
+                /* Prepare a minimal environment for the child. */
+                envsize = 5;
+                child_env = xcalloc(sizeof(*child_env), envsize);
+                child_set_env(&child_env, &envsize, "PATH", _PATH_STDPATH);
+                child_set_env(&child_env, &envsize, "USER", pw->pw_name);
+                child_set_env(&child_env, &envsize, "LOGNAME", pw->pw_name);
+                child_set_env(&child_env, &envsize, "HOME", pw->pw_dir);
+                if ((cp = getenv("LANG")) != NULL)
+                        child_set_env(&child_env, &envsize, "LANG", cp);
+
+                for (i = 0; i < NSIG; i++)
+                        signal(i, SIG_DFL);
+
+                if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
+                        error("%s: open %s: %s", tag, _PATH_DEVNULL,
+                            strerror(errno));
+                        _exit(1);
+                }
+                if (dup2(devnull, STDIN_FILENO) == -1) {
+                        error("%s: dup2: %s", tag, strerror(errno));
+                        _exit(1);
+                }
+
+                /* Set up stdout as requested; leave stderr in place for now. */
+                fd = -1;
+                if ((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) != 0)
+                        fd = p[1];
+                else if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0)
+                        fd = devnull;
+                if (fd != -1 && dup2(fd, STDOUT_FILENO) == -1) {
+                        error("%s: dup2: %s", tag, strerror(errno));
+                        _exit(1);
+                }
+                closefrom(STDERR_FILENO + 1);
+
+                /* Don't use permanently_set_uid() here to avoid fatal() */
+                if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) {
+                        error("%s: setresgid %u: %s", tag, (u_int)pw->pw_gid,
+                            strerror(errno));
+                        _exit(1);
+                }
+                if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) {
+                        error("%s: setresuid %u: %s", tag, (u_int)pw->pw_uid,
+                            strerror(errno));
+                        _exit(1);
+                }
+                /* stdin is pointed to /dev/null at this point */
+                if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0 &&
+                    dup2(STDIN_FILENO, STDERR_FILENO) == -1) {
+                        error("%s: dup2: %s", tag, strerror(errno));
+                        _exit(1);
+                }
+
+                execve(av[0], av, child_env);
+                error("%s exec \"%s\": %s", tag, command, strerror(errno));
+                _exit(127);
+        default: /* parent */
+                break;
+        }
+
+        close(p[1]);
+        if ((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) == 0)
+                close(p[0]);
+        else if ((f = fdopen(p[0], "r")) == NULL) {
+                error("%s: fdopen: %s", tag, strerror(errno));
+                close(p[0]);
+                /* Don't leave zombie child */
+                kill(pid, SIGTERM);
+                while (waitpid(pid, NULL, 0) == -1 && errno == EINTR)
+                        ;
+                return 0;
+        }
+        /* Success */
+        debug3("%s: %s pid %ld", __func__, tag, (long)pid);
+        if (child != NULL)
+                *child = f;
+        return pid;
+}
+
+/* These functions link key/cert options to the auth framework */
+
+/* Log sshauthopt options locally and (optionally) for remote transmission */
+void
+auth_log_authopts(const char *loc, const struct sshauthopt *opts, int do_remote)
+{
+        int do_env = options.permit_user_env && opts->nenv > 0;
+        int do_permitopen = opts->npermitopen > 0 &&
+            (options.allow_tcp_forwarding & FORWARD_LOCAL) != 0;
+        size_t i;
+        char msg[1024], buf[64];
+
+        snprintf(buf, sizeof(buf), "%d", opts->force_tun_device);
+        /* Try to keep this alphabetically sorted */
+        snprintf(msg, sizeof(msg), "key options:%s%s%s%s%s%s%s%s%s%s%s%s",
+            opts->permit_agent_forwarding_flag ? " agent-forwarding" : "",
+            opts->force_command == NULL ? "" : " command",
+            do_env ?  " environment" : "",
+            opts->valid_before == 0 ? "" : "expires",
+            do_permitopen ?  " permitopen" : "",
+            opts->permit_port_forwarding_flag ? " port-forwarding" : "",
+            opts->cert_principals == NULL ? "" : " principals",
+            opts->permit_pty_flag ? " pty" : "",
+            opts->force_tun_device == -1 ? "" : " tun=",
+            opts->force_tun_device == -1 ? "" : buf,
+            opts->permit_user_rc ? " user-rc" : "",
+            opts->permit_x11_forwarding_flag ? " x11-forwarding" : "");
+
+        debug("%s: %s", loc, msg);
+        if (do_remote)
+                auth_debug_add("%s: %s", loc, msg);
+
+        if (options.permit_user_env) {
+                for (i = 0; i < opts->nenv; i++) {
+                        debug("%s: environment: %s", loc, opts->env[i]);
+                        if (do_remote) {
+                                auth_debug_add("%s: environment: %s",
+                                    loc, opts->env[i]);
+                        }
+                }
+        }
+
+        /* Go into a little more details for the local logs. */
+        if (opts->valid_before != 0) {
+                format_absolute_time(opts->valid_before, buf, sizeof(buf));
+                debug("%s: expires at %s", loc, buf);
+        }
+        if (opts->cert_principals != NULL) {
+                debug("%s: authorized principals: \"%s\"",
+                    loc, opts->cert_principals);
+        }
+        if (opts->force_command != NULL)
+                debug("%s: forced command: \"%s\"", loc, opts->force_command);
+        if ((options.allow_tcp_forwarding & FORWARD_LOCAL) != 0) {
+                for (i = 0; i < opts->npermitopen; i++) {
+                        debug("%s: permitted open: %s",
+                            loc, opts->permitopen[i]);
+                }
+        }
+}
+
+/* Activate a new set of key/cert options; merging with what is there. */
+int
+auth_activate_options(struct ssh *ssh, struct sshauthopt *opts)
+{
+        struct sshauthopt *old = auth_opts;
+        const char *emsg = NULL;
+
+        debug("%s: setting new authentication options", __func__);
+        if ((auth_opts = sshauthopt_merge(old, opts, &emsg)) == NULL) {
+                error("Inconsistent authentication options: %s", emsg);
+                return -1;
+        }
+        return 0;
+}
+
+/* Disable forwarding, etc for the session */
+void
+auth_restrict_session(struct ssh *ssh)
+{
+        struct sshauthopt *restricted;
+
+        debug("%s: restricting session", __func__);
+
+        /* A blank sshauthopt defaults to permitting nothing */
+        restricted = sshauthopt_new();
+        restricted->restricted = 1;
+
+        if (auth_activate_options(ssh, restricted) != 0)
+                fatal("%s: failed to restrict session", __func__);
+        sshauthopt_free(restricted);
+}
+
+int
+auth_authorise_keyopts(struct ssh *ssh, struct passwd *pw,
+    struct sshauthopt *opts, int allow_cert_authority, const char *loc)
+{
+        const char *remote_ip = ssh_remote_ipaddr(ssh);
+        const char *remote_host = auth_get_canonical_hostname(ssh,
+            options.use_dns);
+        time_t now = time(NULL);
+        char buf[64];
+
+        /*
+         * Check keys/principals file expiry time.
+         * NB. validity interval in certificate is handled elsewhere.
+         */
+        if (opts->valid_before && now > 0 &&
+            opts->valid_before < (uint64_t)now) {
+                format_absolute_time(opts->valid_before, buf, sizeof(buf));
+                debug("%s: entry expired at %s", loc, buf);
+                auth_debug_add("%s: entry expired at %s", loc, buf);
+                return -1;
+        }
+        /* Consistency checks */
+        if (opts->cert_principals != NULL && !opts->cert_authority) {
+                debug("%s: principals on non-CA key", loc);
+                auth_debug_add("%s: principals on non-CA key", loc);
+                /* deny access */
+                return -1;
+        }
+        /* cert-authority flag isn't valid in authorized_principals files */
+        if (!allow_cert_authority && opts->cert_authority) {
+                debug("%s: cert-authority flag invalid here", loc);
+                auth_debug_add("%s: cert-authority flag invalid here", loc);
+                /* deny access */
+                return -1;
+        }
+
+        /* Perform from= checks */
+        if (opts->required_from_host_keys != NULL) {
+                switch (match_host_and_ip(remote_host, remote_ip,
+                    opts->required_from_host_keys )) {
+                case 1:
+                        /* Host name matches. */
+                        break;
+                case -1:
+                default:
+                        debug("%s: invalid from criteria", loc);
+                        auth_debug_add("%s: invalid from criteria", loc);
+                        /* FALLTHROUGH */
+                case 0:
+                        logit("%s: Authentication tried for %.100s with "
+                            "correct key but not from a permitted "
+                            "host (host=%.200s, ip=%.200s, required=%.200s).",
+                            loc, pw->pw_name, remote_host, remote_ip,
+                            opts->required_from_host_keys);
+                        auth_debug_add("%s: Your host '%.200s' is not "
+                            "permitted to use this key for login.",
+                            loc, remote_host);
+                        /* deny access */
+                        return -1;
+                }
+        }
+        /* Check source-address restriction from certificate */
+        if (opts->required_from_host_cert != NULL) {
+                switch (addr_match_cidr_list(remote_ip,
+                    opts->required_from_host_cert)) {
+                case 1:
+                        /* accepted */
+                        break;
+                case -1:
+                default:
+                        /* invalid */
+                        error("%s: Certificate source-address invalid",
+                            loc);
+                        /* FALLTHROUGH */
+                case 0:
+                        logit("%s: Authentication tried for %.100s with valid "
+                            "certificate but not from a permitted source "
+                            "address (%.200s).", loc, pw->pw_name, remote_ip);
+                        auth_debug_add("%s: Your address '%.200s' is not "
+                            "permitted to use this certificate for login.",
+                            loc, remote_ip);
+                        return -1;
+                }
+        }
+        /*
+         *
+         * XXX this is spammy. We should report remotely only for keys
+         *     that are successful in actual auth attempts, and not PK_OK
+         *     tests.
+         */
+        auth_log_authopts(loc, opts, 1);
+
+        return 0;
+}