/* $OpenBSD: auth2.c,v 1.149 2018/07/11 18:53:29 markus Exp $ */ /* * Copyright (c) 2000 Markus Friedl. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ #include "includes.h" #include #include #include #include #include #include #include #include #include #include "atomicio.h" #include "xmalloc.h" #include "ssh2.h" #include "packet.h" #include "log.h" #include "sshbuf.h" #include "misc.h" #include "servconf.h" #include "compat.h" #include "sshkey.h" #include "hostfile.h" #include "auth.h" #include "dispatch.h" #include "pathnames.h" #include "sshbuf.h" #include "ssherr.h" #ifdef GSSAPI #include "ssh-gss.h" #endif #include "monitor_wrap.h" #include "ssherr.h" #include "digest.h" /* import */ extern ServerOptions options; extern u_char *session_id2; extern u_int session_id2_len; extern struct sshbuf *loginmsg; /* methods */ extern Authmethod method_none; extern Authmethod method_pubkey; extern Authmethod method_passwd; extern Authmethod method_kbdint; extern Authmethod method_hostbased; #ifdef GSSAPI extern Authmethod method_gsskeyex; extern Authmethod method_gssapi; #endif Authmethod *authmethods[] = { &method_none, &method_pubkey, #ifdef GSSAPI &method_gsskeyex, &method_gssapi, #endif &method_passwd, &method_kbdint, &method_hostbased, NULL }; /* protocol */ static int input_service_request(int, u_int32_t, struct ssh *); static int input_userauth_request(int, u_int32_t, struct ssh *); /* helper */ static Authmethod *authmethod_lookup(Authctxt *, const char *); static char *authmethods_get(Authctxt *authctxt); #define MATCH_NONE 0 /* method or submethod mismatch */ #define MATCH_METHOD 1 /* method matches (no submethod specified) */ #define MATCH_BOTH 2 /* method and submethod match */ #define MATCH_PARTIAL 3 /* method matches, submethod can't be checked */ static int list_starts_with(const char *, const char *, const char *); char * auth2_read_banner(void) { struct stat st; char *banner = NULL; size_t len, n; int fd; if ((fd = open(options.banner, O_RDONLY)) == -1) return (NULL); if (fstat(fd, &st) == -1) { close(fd); return (NULL); } if (st.st_size <= 0 || st.st_size > 1*1024*1024) { close(fd); return (NULL); } len = (size_t)st.st_size; /* truncate */ banner = xmalloc(len + 1); n = atomicio(read, fd, banner, len); close(fd); if (n != len) { free(banner); return (NULL); } banner[n] = '\0'; return (banner); } void userauth_send_banner(const char *msg) { packet_start(SSH2_MSG_USERAUTH_BANNER); packet_put_cstring(msg); packet_put_cstring(""); /* language, unused */ packet_send(); debug("%s: sent", __func__); } static void userauth_banner(void) { char *banner = NULL; if (options.banner == NULL) return; if ((banner = PRIVSEP(auth2_read_banner())) == NULL) goto done; userauth_send_banner(banner); done: free(banner); } /* * loop until authctxt->success == TRUE */ void do_authentication2(Authctxt *authctxt) { struct ssh *ssh = active_state; /* XXX */ ssh->authctxt = authctxt; /* XXX move to caller */ ssh_dispatch_init(ssh, &dispatch_protocol_error); ssh_dispatch_set(ssh, SSH2_MSG_SERVICE_REQUEST, &input_service_request); ssh_dispatch_run_fatal(ssh, DISPATCH_BLOCK, &authctxt->success); ssh->authctxt = NULL; } /*ARGSUSED*/ static int input_service_request(int type, u_int32_t seq, struct ssh *ssh) { Authctxt *authctxt = ssh->authctxt; u_int len; int acceptit = 0; char *service = packet_get_cstring(&len); packet_check_eom(); if (authctxt == NULL) fatal("input_service_request: no authctxt"); if (strcmp(service, "ssh-userauth") == 0) { if (!authctxt->success) { acceptit = 1; /* now we can handle user-auth requests */ ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request); } } /* XXX all other service requests are denied */ if (acceptit) { packet_start(SSH2_MSG_SERVICE_ACCEPT); packet_put_cstring(service); packet_send(); packet_write_wait(); } else { debug("bad service request %s", service); packet_disconnect("bad service request %s", service); } free(service); return 0; } #define MIN_FAIL_DELAY_SECONDS 0.005 static double user_specific_delay(const char *user) { char b[512]; size_t len = ssh_digest_bytes(SSH_DIGEST_SHA512); u_char *hash = xmalloc(len); double delay; (void)snprintf(b, sizeof b, "%llu%s", (unsigned long long)options.timing_secret, user); if (ssh_digest_memory(SSH_DIGEST_SHA512, b, strlen(b), hash, len) != 0) fatal("%s: ssh_digest_memory", __func__); /* 0-4.2 ms of delay */ delay = (double)PEEK_U32(hash) / 1000 / 1000 / 1000 / 1000; freezero(hash, len); debug3("%s: user specific delay %0.3lfms", __func__, delay/1000); return MIN_FAIL_DELAY_SECONDS + delay; } static void ensure_minimum_time_since(double start, double seconds) { struct timespec ts; double elapsed = monotime_double() - start, req = seconds, remain; /* if we've already passed the requested time, scale up */ while ((remain = seconds - elapsed) < 0.0) seconds *= 2; ts.tv_sec = remain; ts.tv_nsec = (remain - ts.tv_sec) * 1000000000; debug3("%s: elapsed %0.3lfms, delaying %0.3lfms (requested %0.3lfms)", __func__, elapsed*1000, remain*1000, req*1000); nanosleep(&ts, NULL); } /*ARGSUSED*/ static int input_userauth_request(int type, u_int32_t seq, struct ssh *ssh) { Authctxt *authctxt = ssh->authctxt; Authmethod *m = NULL; char *user, *service, *method, *style = NULL; int authenticated = 0; double tstart = monotime_double(); if (authctxt == NULL) fatal("input_userauth_request: no authctxt"); user = packet_get_cstring(NULL); service = packet_get_cstring(NULL); method = packet_get_cstring(NULL); debug("userauth-request for user %s service %s method %s", user, service, method); debug("attempt %d failures %d", authctxt->attempt, authctxt->failures); if ((style = strchr(user, ':')) != NULL) *style++ = 0; if (authctxt->attempt++ == 0) { /* setup auth context */ authctxt->pw = PRIVSEP(getpwnamallow(user)); authctxt->user = xstrdup(user); if (authctxt->pw && strcmp(service, "ssh-connection")==0) { authctxt->valid = 1; debug2("%s: setting up authctxt for %s", __func__, user); } else { /* Invalid user, fake password information */ authctxt->pw = fakepw(); #ifdef SSH_AUDIT_EVENTS PRIVSEP(audit_event(SSH_INVALID_USER)); #endif } #ifdef USE_PAM if (options.use_pam) PRIVSEP(start_pam(authctxt)); #endif ssh_packet_set_log_preamble(ssh, "%suser %s", authctxt->valid ? "authenticating " : "invalid ", user); setproctitle("%s%s", authctxt->valid ? user : "unknown", use_privsep ? " [net]" : ""); authctxt->service = xstrdup(service); authctxt->style = style ? xstrdup(style) : NULL; if (use_privsep) mm_inform_authserv(service, style); userauth_banner(); if (auth2_setup_methods_lists(authctxt) != 0) packet_disconnect("no authentication methods enabled"); } else if (strcmp(user, authctxt->user) != 0 || strcmp(service, authctxt->service) != 0) { packet_disconnect("Change of username or service not allowed: " "(%s,%s) -> (%s,%s)", authctxt->user, authctxt->service, user, service); } /* reset state */ auth2_challenge_stop(ssh); #ifdef GSSAPI /* XXX move to auth2_gssapi_stop() */ ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL); ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL); #endif auth2_authctxt_reset_info(authctxt); authctxt->postponed = 0; authctxt->server_caused_failure = 0; /* try to authenticate user */ m = authmethod_lookup(authctxt, method); if (m != NULL && authctxt->failures < options.max_authtries) { debug2("input_userauth_request: try method %s", method); authenticated = m->userauth(ssh); } if (!authctxt->authenticated) ensure_minimum_time_since(tstart, user_specific_delay(authctxt->user)); userauth_finish(ssh, authenticated, method, NULL); free(service); free(user); free(method); return 0; } void userauth_finish(struct ssh *ssh, int authenticated, const char *method, const char *submethod) { Authctxt *authctxt = ssh->authctxt; char *methods; int partial = 0; if (!authctxt->valid && authenticated) fatal("INTERNAL ERROR: authenticated invalid user %s", authctxt->user); if (authenticated && authctxt->postponed) fatal("INTERNAL ERROR: authenticated and postponed"); /* Special handling for root */ if (authenticated && authctxt->pw->pw_uid == 0 && !auth_root_allowed(ssh, method)) { authenticated = 0; #ifdef SSH_AUDIT_EVENTS PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED)); #endif } if (authenticated && options.num_auth_methods != 0) { if (!auth2_update_methods_lists(authctxt, method, submethod)) { authenticated = 0; partial = 1; } } /* Log before sending the reply */ auth_log(authctxt, authenticated, partial, method, submethod); /* Update information exposed to session */ if (authenticated || partial) auth2_update_session_info(authctxt, method, submethod); if (authctxt->postponed) return; #ifdef USE_PAM if (options.use_pam && authenticated) { int r; if (!PRIVSEP(do_pam_account())) { /* if PAM returned a message, send it to the user */ if (sshbuf_len(loginmsg) > 0) { if ((r = sshbuf_put(loginmsg, "\0", 1)) != 0) fatal("%s: buffer error: %s", __func__, ssh_err(r)); userauth_send_banner(sshbuf_ptr(loginmsg)); packet_write_wait(); } fatal("Access denied for user %s by PAM account " "configuration", authctxt->user); } } #endif if (authenticated == 1) { /* turn off userauth */ ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore); packet_start(SSH2_MSG_USERAUTH_SUCCESS); packet_send(); packet_write_wait(); /* now we can break out */ authctxt->success = 1; ssh_packet_set_log_preamble(ssh, "user %s", authctxt->user); } else { /* Allow initial try of "none" auth without failure penalty */ if (!partial && !authctxt->server_caused_failure && (authctxt->attempt > 1 || strcmp(method, "none") != 0)) authctxt->failures++; if (authctxt->failures >= options.max_authtries) { #ifdef SSH_AUDIT_EVENTS PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES)); #endif auth_maxtries_exceeded(authctxt); } methods = authmethods_get(authctxt); debug3("%s: failure partial=%d next methods=\"%s\"", __func__, partial, methods); packet_start(SSH2_MSG_USERAUTH_FAILURE); packet_put_cstring(methods); packet_put_char(partial); packet_send(); packet_write_wait(); free(methods); } } /* * Checks whether method is allowed by at least one AuthenticationMethods * methods list. Returns 1 if allowed, or no methods lists configured. * 0 otherwise. */ int auth2_method_allowed(Authctxt *authctxt, const char *method, const char *submethod) { u_int i; /* * NB. authctxt->num_auth_methods might be zero as a result of * auth2_setup_methods_lists(), so check the configuration. */ if (options.num_auth_methods == 0) return 1; for (i = 0; i < authctxt->num_auth_methods; i++) { if (list_starts_with(authctxt->auth_methods[i], method, submethod) != MATCH_NONE) return 1; } return 0; } static char * authmethods_get(Authctxt *authctxt) { struct sshbuf *b; char *list; int i, r; if ((b = sshbuf_new()) == NULL) fatal("%s: sshbuf_new failed", __func__); for (i = 0; authmethods[i] != NULL; i++) { if (strcmp(authmethods[i]->name, "none") == 0) continue; if (authmethods[i]->enabled == NULL || *(authmethods[i]->enabled) == 0) continue; if (!auth2_method_allowed(authctxt, authmethods[i]->name, NULL)) continue; if ((r = sshbuf_putf(b, "%s%s", sshbuf_len(b) ? "," : "", authmethods[i]->name)) != 0) fatal("%s: buffer error: %s", __func__, ssh_err(r)); } if ((list = sshbuf_dup_string(b)) == NULL) fatal("%s: sshbuf_dup_string failed", __func__); sshbuf_free(b); return list; } static Authmethod * authmethod_lookup(Authctxt *authctxt, const char *name) { int i; if (name != NULL) for (i = 0; authmethods[i] != NULL; i++) if (authmethods[i]->enabled != NULL && *(authmethods[i]->enabled) != 0 && strcmp(name, authmethods[i]->name) == 0 && auth2_method_allowed(authctxt, authmethods[i]->name, NULL)) return authmethods[i]; debug2("Unrecognized authentication method name: %s", name ? name : "NULL"); return NULL; } /* * Check a comma-separated list of methods for validity. Is need_enable is * non-zero, then also require that the methods are enabled. * Returns 0 on success or -1 if the methods list is invalid. */ int auth2_methods_valid(const char *_methods, int need_enable) { char *methods, *omethods, *method, *p; u_int i, found; int ret = -1; if (*_methods == '\0') { error("empty authentication method list"); return -1; } omethods = methods = xstrdup(_methods); while ((method = strsep(&methods, ",")) != NULL) { for (found = i = 0; !found && authmethods[i] != NULL; i++) { if ((p = strchr(method, ':')) != NULL) *p = '\0'; if (strcmp(method, authmethods[i]->name) != 0) continue; if (need_enable) { if (authmethods[i]->enabled == NULL || *(authmethods[i]->enabled) == 0) { error("Disabled method \"%s\" in " "AuthenticationMethods list \"%s\"", method, _methods); goto out; } } found = 1; break; } if (!found) { error("Unknown authentication method \"%s\" in list", method); goto out; } } ret = 0; out: free(omethods); return ret; } /* * Prune the AuthenticationMethods supplied in the configuration, removing * any methods lists that include disabled methods. Note that this might * leave authctxt->num_auth_methods == 0, even when multiple required auth * has been requested. For this reason, all tests for whether multiple is * enabled should consult options.num_auth_methods directly. */ int auth2_setup_methods_lists(Authctxt *authctxt) { u_int i; if (options.num_auth_methods == 0) return 0; debug3("%s: checking methods", __func__); authctxt->auth_methods = xcalloc(options.num_auth_methods, sizeof(*authctxt->auth_methods)); authctxt->num_auth_methods = 0; for (i = 0; i < options.num_auth_methods; i++) { if (auth2_methods_valid(options.auth_methods[i], 1) != 0) { logit("Authentication methods list \"%s\" contains " "disabled method, skipping", options.auth_methods[i]); continue; } debug("authentication methods list %d: %s", authctxt->num_auth_methods, options.auth_methods[i]); authctxt->auth_methods[authctxt->num_auth_methods++] = xstrdup(options.auth_methods[i]); } if (authctxt->num_auth_methods == 0) { error("No AuthenticationMethods left after eliminating " "disabled methods"); return -1; } return 0; } static int list_starts_with(const char *methods, const char *method, const char *submethod) { size_t l = strlen(method); int match; const char *p; if (strncmp(methods, method, l) != 0) return MATCH_NONE; p = methods + l; match = MATCH_METHOD; if (*p == ':') { if (!submethod) return MATCH_PARTIAL; l = strlen(submethod); p += 1; if (strncmp(submethod, p, l)) return MATCH_NONE; p += l; match = MATCH_BOTH; } if (*p != ',' && *p != '\0') return MATCH_NONE; return match; } /* * Remove method from the start of a comma-separated list of methods. * Returns 0 if the list of methods did not start with that method or 1 * if it did. */ static int remove_method(char **methods, const char *method, const char *submethod) { char *omethods = *methods, *p; size_t l = strlen(method); int match; match = list_starts_with(omethods, method, submethod); if (match != MATCH_METHOD && match != MATCH_BOTH) return 0; p = omethods + l; if (submethod && match == MATCH_BOTH) p += 1 + strlen(submethod); /* include colon */ if (*p == ',') p++; *methods = xstrdup(p); free(omethods); return 1; } /* * Called after successful authentication. Will remove the successful method * from the start of each list in which it occurs. If it was the last method * in any list, then authentication is deemed successful. * Returns 1 if the method completed any authentication list or 0 otherwise. */ int auth2_update_methods_lists(Authctxt *authctxt, const char *method, const char *submethod) { u_int i, found = 0; debug3("%s: updating methods list after \"%s\"", __func__, method); for (i = 0; i < authctxt->num_auth_methods; i++) { if (!remove_method(&(authctxt->auth_methods[i]), method, submethod)) continue; found = 1; if (*authctxt->auth_methods[i] == '\0') { debug2("authentication methods list %d complete", i); return 1; } debug3("authentication methods list %d remaining: \"%s\"", i, authctxt->auth_methods[i]); } /* This should not happen, but would be bad if it did */ if (!found) fatal("%s: method not in AuthenticationMethods", __func__); return 0; } /* Reset method-specific information */ void auth2_authctxt_reset_info(Authctxt *authctxt) { sshkey_free(authctxt->auth_method_key); free(authctxt->auth_method_info); authctxt->auth_method_key = NULL; authctxt->auth_method_info = NULL; } /* Record auth method-specific information for logs */ void auth2_record_info(Authctxt *authctxt, const char *fmt, ...) { va_list ap; int i; free(authctxt->auth_method_info); authctxt->auth_method_info = NULL; va_start(ap, fmt); i = vasprintf(&authctxt->auth_method_info, fmt, ap); va_end(ap); if (i < 0 || authctxt->auth_method_info == NULL) fatal("%s: vasprintf failed", __func__); } /* * Records a public key used in authentication. This is used for logging * and to ensure that the same key is not subsequently accepted again for * multiple authentication. */ void auth2_record_key(Authctxt *authctxt, int authenticated, const struct sshkey *key) { struct sshkey **tmp, *dup; int r; if ((r = sshkey_demote(key, &dup)) != 0) fatal("%s: copy key: %s", __func__, ssh_err(r)); sshkey_free(authctxt->auth_method_key); authctxt->auth_method_key = dup; if (!authenticated) return; /* If authenticated, make sure we don't accept this key again */ if ((r = sshkey_demote(key, &dup)) != 0) fatal("%s: copy key: %s", __func__, ssh_err(r)); if (authctxt->nprev_keys >= INT_MAX || (tmp = recallocarray(authctxt->prev_keys, authctxt->nprev_keys, authctxt->nprev_keys + 1, sizeof(*authctxt->prev_keys))) == NULL) fatal("%s: reallocarray failed", __func__); authctxt->prev_keys = tmp; authctxt->prev_keys[authctxt->nprev_keys] = dup; authctxt->nprev_keys++; } /* Checks whether a key has already been previously used for authentication */ int auth2_key_already_used(Authctxt *authctxt, const struct sshkey *key) { u_int i; char *fp; for (i = 0; i < authctxt->nprev_keys; i++) { if (sshkey_equal_public(key, authctxt->prev_keys[i])) { fp = sshkey_fingerprint(authctxt->prev_keys[i], options.fingerprint_hash, SSH_FP_DEFAULT); debug3("%s: key already used: %s %s", __func__, sshkey_type(authctxt->prev_keys[i]), fp == NULL ? "UNKNOWN" : fp); free(fp); return 1; } } return 0; } /* * Updates authctxt->session_info with details of authentication. Should be * whenever an authentication method succeeds. */ void auth2_update_session_info(Authctxt *authctxt, const char *method, const char *submethod) { int r; if (authctxt->session_info == NULL) { if ((authctxt->session_info = sshbuf_new()) == NULL) fatal("%s: sshbuf_new", __func__); } /* Append method[/submethod] */ if ((r = sshbuf_putf(authctxt->session_info, "%s%s%s", method, submethod == NULL ? "" : "/", submethod == NULL ? "" : submethod)) != 0) fatal("%s: append method: %s", __func__, ssh_err(r)); /* Append key if present */ if (authctxt->auth_method_key != NULL) { if ((r = sshbuf_put_u8(authctxt->session_info, ' ')) != 0 || (r = sshkey_format_text(authctxt->auth_method_key, authctxt->session_info)) != 0) fatal("%s: append key: %s", __func__, ssh_err(r)); } if (authctxt->auth_method_info != NULL) { /* Ensure no ambiguity here */ if (strchr(authctxt->auth_method_info, '\n') != NULL) fatal("%s: auth_method_info contains \\n", __func__); if ((r = sshbuf_put_u8(authctxt->session_info, ' ')) != 0 || (r = sshbuf_putf(authctxt->session_info, "%s", authctxt->auth_method_info)) != 0) { fatal("%s: append method info: %s", __func__, ssh_err(r)); } } if ((r = sshbuf_put_u8(authctxt->session_info, '\n')) != 0) fatal("%s: append: %s", __func__, ssh_err(r)); }