diff options
Diffstat (limited to 'auth.c')
| -rw-r--r-- | auth.c | 351 |
1 files changed, 346 insertions, 5 deletions
@@ -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; @@ -399,7 +400,7 @@ 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; } @@ -840,3 +841,343 @@ 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; +} |