/* $NetBSD: auth2-pubkey.c,v 1.10 2014/10/19 16:30:58 christos Exp $ */ /* $OpenBSD: auth2-pubkey.c,v 1.41 2014/07/15 15:54:14 millert 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" __RCSID("$NetBSD: auth2-pubkey.c,v 1.10 2014/10/19 16:30:58 christos Exp $"); #include #include #include #include #include #include #include #include #include #include #include #include #include #include "xmalloc.h" #include "ssh.h" #include "ssh2.h" #include "packet.h" #include "buffer.h" #include "log.h" #include "misc.h" #include "servconf.h" #include "compat.h" #include "key.h" #include "hostfile.h" #include "auth.h" #include "pathnames.h" #include "uidswap.h" #include "auth-options.h" #include "canohost.h" #ifdef GSSAPI #include "ssh-gss.h" #endif #include "monitor_wrap.h" #include "authfile.h" #include "match.h" #ifdef WITH_LDAP_PUBKEY #include "ldapauth.h" #endif /* import */ extern ServerOptions options; extern u_char *session_id2; extern u_int session_id2_len; static int userauth_pubkey(Authctxt *authctxt) { Buffer b; Key *key = NULL; char *pkalg, *userstyle; u_char *pkblob, *sig; u_int alen, blen, slen; int have_sig, pktype; int authenticated = 0; if (!authctxt->valid) { debug2("userauth_pubkey: disabled because of invalid user"); return 0; } have_sig = packet_get_char(); if (datafellows & SSH_BUG_PKAUTH) { debug2("userauth_pubkey: SSH_BUG_PKAUTH"); /* no explicit pkalg given */ pkblob = packet_get_string(&blen); buffer_init(&b); buffer_append(&b, pkblob, blen); /* so we have to extract the pkalg from the pkblob */ pkalg = buffer_get_string(&b, &alen); buffer_free(&b); } else { pkalg = packet_get_string(&alen); pkblob = packet_get_string(&blen); } pktype = key_type_from_name(pkalg); if (pktype == KEY_UNSPEC) { /* this is perfectly legal */ logit("userauth_pubkey: unsupported public key algorithm: %s", pkalg); goto done; } key = key_from_blob(pkblob, blen); if (key == NULL) { error("userauth_pubkey: cannot decode key: %s", pkalg); goto done; } if (key->type != pktype) { error("userauth_pubkey: type mismatch for decoded key " "(received %d, expected %d)", key->type, pktype); goto done; } if (key_type_plain(key->type) == KEY_RSA && (datafellows & SSH_BUG_RSASIGMD5) != 0) { logit("Refusing RSA key because client uses unsafe " "signature scheme"); goto done; } if (have_sig) { sig = packet_get_string(&slen); packet_check_eom(); buffer_init(&b); if (datafellows & SSH_OLD_SESSIONID) { buffer_append(&b, session_id2, session_id2_len); } else { buffer_put_string(&b, session_id2, session_id2_len); } /* reconstruct packet */ buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); xasprintf(&userstyle, "%s%s%s", authctxt->user, authctxt->style ? ":" : "", authctxt->style ? authctxt->style : ""); buffer_put_cstring(&b, userstyle); free(userstyle); buffer_put_cstring(&b, datafellows & SSH_BUG_PKSERVICE ? "ssh-userauth" : authctxt->service); if (datafellows & SSH_BUG_PKAUTH) { buffer_put_char(&b, have_sig); } else { buffer_put_cstring(&b, "publickey"); buffer_put_char(&b, have_sig); buffer_put_cstring(&b, pkalg); } buffer_put_string(&b, pkblob, blen); #ifdef DEBUG_PK buffer_dump(&b); #endif pubkey_auth_info(authctxt, key, NULL); /* test for correct signature */ authenticated = 0; if (PRIVSEP(user_key_allowed(authctxt->pw, key)) && PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), buffer_len(&b))) == 1) authenticated = 1; buffer_free(&b); free(sig); } else { debug("test whether pkalg/pkblob are acceptable"); packet_check_eom(); /* XXX fake reply and always send PK_OK ? */ /* * XXX this allows testing whether a user is allowed * to login: if you happen to have a valid pubkey this * message is sent. the message is NEVER sent at all * if a user is not allowed to login. is this an * issue? -markus */ if (PRIVSEP(user_key_allowed(authctxt->pw, key))) { packet_start(SSH2_MSG_USERAUTH_PK_OK); packet_put_string(pkalg, alen); packet_put_string(pkblob, blen); packet_send(); packet_write_wait(); authctxt->postponed = 1; } } if (authenticated != 1) auth_clear_options(); done: debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg); if (key != NULL) key_free(key); free(pkalg); free(pkblob); return authenticated; } void pubkey_auth_info(Authctxt *authctxt, const Key *key, const char *fmt, ...) { char *fp, *extra; va_list ap; int i; extra = NULL; if (fmt != NULL) { va_start(ap, fmt); i = vasprintf(&extra, fmt, ap); va_end(ap); if (i < 0 || extra == NULL) fatal("%s: vasprintf failed", __func__); } if (key_is_cert(key)) { fp = key_fingerprint(key->cert->signature_key, SSH_FP_MD5, SSH_FP_HEX); auth_info(authctxt, "%s ID %s (serial %llu) CA %s %s%s%s", key_type(key), key->cert->key_id, (unsigned long long)key->cert->serial, key_type(key->cert->signature_key), fp, extra == NULL ? "" : ", ", extra == NULL ? "" : extra); free(fp); } else { fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); auth_info(authctxt, "%s %s%s%s", key_type(key), fp, extra == NULL ? "" : ", ", extra == NULL ? "" : extra); free(fp); } free(extra); } static int match_principals_option(const char *principal_list, struct sshkey_cert *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); free(result); return 1; } } return 0; } static int match_principals_file(char *file, struct passwd *pw, struct sshkey_cert *cert) { FILE *f; char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts; 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. */ for (cp = line; *cp == ' ' || *cp == '\t'; cp++) ; /* Skip blank and comment lines. */ if ((ep = strchr(cp, '#')) != NULL) *ep = '\0'; if (!*cp || *cp == '\n') continue; /* Trim trailing whitespace. */ ep = cp + strlen(cp) - 1; while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t')) *ep-- = '\0'; /* * If the line has internal whitespace then assume it has * key options. */ line_opts = NULL; if ((ep = strrchr(cp, ' ')) != NULL || (ep = strrchr(cp, '\t')) != NULL) { for (; *ep == ' ' || *ep == '\t'; ep++) ; line_opts = cp; cp = ep; } for (i = 0; i < cert->nprincipals; i++) { if (strcmp(cp, cert->principals[i]) == 0) { debug3("matched principal \"%.100s\" " "from file \"%s\" on line %lu", cert->principals[i], file, linenum); if (auth_parse_options(pw, line_opts, file, linenum) != 1) continue; fclose(f); restore_uid(); return 1; } } } fclose(f); restore_uid(); return 0; } /* * Checks whether key is allowed in authorized_keys-format file, * returns 1 if the key is allowed or 0 otherwise. */ static int check_authkeys_file(FILE *f, char *file, Key* key, struct passwd *pw) { char line[SSH_MAX_PUBKEY_BYTES]; const char *reason; int found_key = 0; u_long linenum = 0; Key *found; char *fp; #ifdef WITH_LDAP_PUBKEY ldap_key_t * k; unsigned int i = 0; #endif #ifdef WITH_LDAP_PUBKEY found_key = 0; /* allocate a new key type */ found = key_new(key->type); /* first check if the options is enabled, then try.. */ if (options.lpk.on) { debug("[LDAP] trying LDAP first uid=%s",pw->pw_name); if (ldap_ismember(&options.lpk, pw->pw_name) > 0) { if ((k = ldap_getuserkey(&options.lpk, pw->pw_name)) != NULL) { /* Skip leading whitespace, empty and comment lines. */ for (i = 0 ; i < k->num ; i++) { /* dont forget if multiple keys to reset options */ char *cp, *xoptions = NULL; for (cp = (char *)k->keys[i]->bv_val; *cp == ' ' || *cp == '\t'; cp++) ; if (!*cp || *cp == '\n' || *cp == '#') continue; if (key_read(found, &cp) != 1) { /* no key? check if there are options for this key */ int quoted = 0; debug2("[LDAP] user_key_allowed: check options: '%s'", cp); xoptions = cp; for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { if (*cp == '\\' && cp[1] == '"') cp++; /* Skip both */ else if (*cp == '"') quoted = !quoted; } /* Skip remaining whitespace. */ for (; *cp == ' ' || *cp == '\t'; cp++) ; if (key_read(found, &cp) != 1) { debug2("[LDAP] user_key_allowed: advance: '%s'", cp); /* still no key? advance to next line*/ continue; } } if (key_equal(found, key) && auth_parse_options(pw, xoptions, file, linenum) == 1) { found_key = 1; debug("[LDAP] matching key found"); fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX); verbose("[LDAP] Found matching %s key: %s", key_type(found), fp); /* restoring memory */ ldap_keys_free(k); free(fp); restore_uid(); key_free(found); return found_key; break; } }/* end of LDAP for() */ } else { logit("[LDAP] no keys found for '%s'!", pw->pw_name); } } else { logit("[LDAP] '%s' is not in '%s'", pw->pw_name, options.lpk.sgroup); } } #endif debug("trying public key file %s", file); f = auth_openkeyfile(file, pw, options.strict_modes); if (!f) { restore_uid(); return 0; } found_key = 0; found = NULL; while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { char *cp, *key_options = NULL; if (found != NULL) key_free(found); found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type); auth_clear_options(); /* Skip leading whitespace, empty and comment lines. */ for (cp = line; *cp == ' ' || *cp == '\t'; cp++) ; if (!*cp || *cp == '\n' || *cp == '#') continue; if (key_read(found, &cp) != 1) { /* no key? check if there are options for this key */ int quoted = 0; debug2("user_key_allowed: check options: '%s'", cp); key_options = cp; for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { if (*cp == '\\' && cp[1] == '"') cp++; /* Skip both */ else if (*cp == '"') quoted = !quoted; } /* Skip remaining whitespace. */ for (; *cp == ' ' || *cp == '\t'; cp++) ; if (key_read(found, &cp) != 1) { debug2("user_key_allowed: advance: '%s'", cp); /* still no key? advance to next line*/ continue; } } if (key_is_cert(key)) { if (!key_equal(found, key->cert->signature_key)) continue; if (auth_parse_options(pw, key_options, file, linenum) != 1) continue; if (!key_is_cert_authority) continue; fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX); debug("matching CA found: file %s, line %lu, %s %s", file, linenum, key_type(found), fp); /* * 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: free(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) { free(fp); continue; } verbose("Accepted certificate ID \"%s\" " "signed by %s CA %s via %s", key->cert->key_id, key_type(found), fp, file); free(fp); found_key = 1; break; } else if (key_equal(found, key)) { if (auth_parse_options(pw, key_options, file, linenum) != 1) continue; if (key_is_cert_authority) continue; found_key = 1; fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX); debug("matching key found: file %s, line %lu %s %s", file, linenum, key_type(found), fp); free(fp); break; } } if (found != NULL) key_free(found); if (!found_key) debug2("key not found"); return found_key; } /* Authenticate a certificate key against TrustedUserCAKeys */ static int user_cert_trusted_ca(struct passwd *pw, Key *key) { char *ca_fp, *principals_file = NULL; const char *reason; int ret = 0; if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL) return 0; ca_fp = key_fingerprint(key->cert->signature_key, SSH_FP_MD5, SSH_FP_HEX); if (key_in_file(key->cert->signature_key, options.trusted_user_ca_keys, 1) != 1) { debug2("%s: CA %s %s is not listed in %s", __func__, key_type(key->cert->signature_key), ca_fp, options.trusted_user_ca_keys); 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; verbose("Accepted certificate ID \"%s\" signed by %s CA %s via %s", key->cert->key_id, key_type(key->cert->signature_key), ca_fp, options.trusted_user_ca_keys); ret = 1; out: free(principals_file); free(ca_fp); return ret; } /* * Checks whether key is allowed in file. * returns 1 if the key is allowed or 0 otherwise. */ static int user_key_allowed2(struct passwd *pw, Key *key, char *file) { FILE *f; int found_key = 0; /* Temporarily use the user's uid. */ temporarily_use_uid(pw); debug("trying public key file %s", file); if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) { found_key = check_authkeys_file(f, file, key, pw); fclose(f); } restore_uid(); return found_key; } /* * Checks whether key is allowed in output of command. * returns 1 if the key is allowed or 0 otherwise. */ static int user_key_command_allowed2(struct passwd *user_pw, Key *key) { FILE *f; int ok, found_key = 0; struct passwd *pw; struct stat st; int status, devnull, p[2], i; pid_t pid; char *username, errmsg[512]; if (options.authorized_keys_command == NULL || options.authorized_keys_command[0] != '/') return 0; if (options.authorized_keys_command_user == NULL) { error("No user for AuthorizedKeysCommand specified, skipping"); return 0; } username = percent_expand(options.authorized_keys_command_user, "u", user_pw->pw_name, (char *)NULL); pw = getpwnam(username); if (pw == NULL) { error("AuthorizedKeysCommandUser \"%s\" not found: %s", username, strerror(errno)); free(username); return 0; } free(username); temporarily_use_uid(pw); if (stat(options.authorized_keys_command, &st) < 0) { error("Could not stat AuthorizedKeysCommand \"%s\": %s", options.authorized_keys_command, strerror(errno)); goto out; } if (auth_secure_path(options.authorized_keys_command, &st, NULL, 0, errmsg, sizeof(errmsg)) != 0) { error("Unsafe AuthorizedKeysCommand: %s", errmsg); goto out; } if (pipe(p) != 0) { error("%s: pipe: %s", __func__, strerror(errno)); goto out; } debug3("Running AuthorizedKeysCommand: \"%s %s\" as \"%s\"", options.authorized_keys_command, user_pw->pw_name, pw->pw_name); /* * Don't want to call this in the child, where it can fatal() and * run cleanup_exit() code. */ restore_uid(); switch ((pid = fork())) { case -1: /* error */ error("%s: fork: %s", __func__, strerror(errno)); close(p[0]); close(p[1]); return 0; case 0: /* child */ for (i = 0; i < NSIG; i++) signal(i, SIG_DFL); if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) { error("%s: open %s: %s", __func__, _PATH_DEVNULL, strerror(errno)); _exit(1); } /* Keep stderr around a while longer to catch errors */ if (dup2(devnull, STDIN_FILENO) == -1 || dup2(p[1], STDOUT_FILENO) == -1) { error("%s: dup2: %s", __func__, strerror(errno)); _exit(1); } closefrom(STDERR_FILENO + 1); /* Don't use permanently_set_uid() here to avoid fatal() */ if (setgid(pw->pw_gid) != 0) { error("setgid %u: %s", (u_int)pw->pw_gid, strerror(errno)); _exit(1); } if (setuid(pw->pw_uid) != 0) { error("setuid %u: %s", (u_int)pw->pw_uid, strerror(errno)); _exit(1); } /* stdin is pointed to /dev/null at this point */ if (dup2(STDIN_FILENO, STDERR_FILENO) == -1) { error("%s: dup2: %s", __func__, strerror(errno)); _exit(1); } execl(options.authorized_keys_command, options.authorized_keys_command, user_pw->pw_name, NULL); error("AuthorizedKeysCommand %s exec failed: %s", options.authorized_keys_command, strerror(errno)); _exit(127); default: /* parent */ break; } temporarily_use_uid(pw); close(p[1]); if ((f = fdopen(p[0], "r")) == NULL) { error("%s: fdopen: %s", __func__, strerror(errno)); close(p[0]); /* Don't leave zombie child */ kill(pid, SIGTERM); while (waitpid(pid, NULL, 0) == -1 && errno == EINTR) ; goto out; } ok = check_authkeys_file(f, options.authorized_keys_command, key, pw); fclose(f); while (waitpid(pid, &status, 0) == -1) { if (errno != EINTR) { error("%s: waitpid: %s", __func__, strerror(errno)); goto out; } } if (WIFSIGNALED(status)) { error("AuthorizedKeysCommand %s exited on signal %d", options.authorized_keys_command, WTERMSIG(status)); goto out; } else if (WEXITSTATUS(status) != 0) { error("AuthorizedKeysCommand %s returned status %d", options.authorized_keys_command, WEXITSTATUS(status)); goto out; } found_key = ok; out: restore_uid(); return found_key; } /* * Check whether key authenticates and authorises the user. */ int user_key_allowed(struct passwd *pw, Key *key) { u_int success, i; char *file; if (auth_key_is_revoked(key)) return 0; if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key)) return 0; success = user_cert_trusted_ca(pw, key); if (success) return success; success = user_key_command_allowed2(pw, key); if (success > 0) return success; for (i = 0; !success && i < options.num_authkeys_files; i++) { if (strcasecmp(options.authorized_keys_files[i], "none") == 0) continue; file = expand_authorized_keys( options.authorized_keys_files[i], pw); success = user_key_allowed2(pw, key, file); free(file); } return success; } Authmethod method_pubkey = { "publickey", userauth_pubkey, &options.pubkey_authentication };