diff options
Diffstat (limited to 'auth2-pubkey.c')
| -rw-r--r-- | auth2-pubkey.c | 1045 |
1 files changed, 1045 insertions, 0 deletions
diff --git a/auth2-pubkey.c b/auth2-pubkey.c new file mode 100644 index 0000000..2fb5950 --- /dev/null +++ b/auth2-pubkey.c @@ -0,0 +1,1045 @@ +/* $OpenBSD: auth2-pubkey.c,v 1.86 2018/09/20 03:28:06 djm 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 <sys/types.h> +#include <sys/stat.h> + +#include <errno.h> +#include <fcntl.h> +#ifdef HAVE_PATHS_H +# include <paths.h> +#endif +#include <pwd.h> +#include <signal.h> +#include <stdio.h> +#include <stdarg.h> +#include <string.h> +#include <time.h> +#include <unistd.h> +#include <limits.h> + +#include "xmalloc.h" +#include "ssh.h" +#include "ssh2.h" +#include "packet.h" +#include "sshbuf.h" +#include "log.h" +#include "misc.h" +#include "servconf.h" +#include "compat.h" +#include "sshkey.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" +#include "ssherr.h" +#include "channels.h" /* XXX for session.h */ +#include "session.h" /* XXX for child_set_env(); refactor? */ + +/* import */ +extern ServerOptions options; +extern u_char *session_id2; +extern u_int session_id2_len; + +static char * +format_key(const struct sshkey *key) +{ + char *ret, *fp = sshkey_fingerprint(key, + options.fingerprint_hash, SSH_FP_DEFAULT); + + xasprintf(&ret, "%s %s", sshkey_type(key), fp); + free(fp); + return ret; +} + +static int +userauth_pubkey(struct ssh *ssh) +{ + Authctxt *authctxt = ssh->authctxt; + struct passwd *pw = authctxt->pw; + struct sshbuf *b = NULL; + struct sshkey *key = NULL; + char *pkalg = NULL, *userstyle = NULL, *key_s = NULL, *ca_s = NULL; + u_char *pkblob = NULL, *sig = NULL, have_sig; + size_t blen, slen; + int r, pktype; + int authenticated = 0; + struct sshauthopt *authopts = NULL; + + if ((r = sshpkt_get_u8(ssh, &have_sig)) != 0 || + (r = sshpkt_get_cstring(ssh, &pkalg, NULL)) != 0 || + (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0) + fatal("%s: parse request failed: %s", __func__, ssh_err(r)); + pktype = sshkey_type_from_name(pkalg); + if (pktype == KEY_UNSPEC) { + /* this is perfectly legal */ + verbose("%s: unsupported public key algorithm: %s", + __func__, pkalg); + goto done; + } + if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { + error("%s: could not parse key: %s", __func__, ssh_err(r)); + goto done; + } + if (key == NULL) { + error("%s: cannot decode key: %s", __func__, pkalg); + goto done; + } + if (key->type != pktype) { + error("%s: type mismatch for decoded key " + "(received %d, expected %d)", __func__, key->type, pktype); + goto done; + } + if (sshkey_type_plain(key->type) == KEY_RSA && + (ssh->compat & SSH_BUG_RSASIGMD5) != 0) { + logit("Refusing RSA key because client uses unsafe " + "signature scheme"); + goto done; + } + if (auth2_key_already_used(authctxt, key)) { + logit("refusing previously-used %s key", sshkey_type(key)); + goto done; + } + if (match_pattern_list(pkalg, options.pubkey_key_types, 0) != 1) { + logit("%s: key type %s not in PubkeyAcceptedKeyTypes", + __func__, sshkey_ssh_name(key)); + goto done; + } + if ((r = sshkey_check_cert_sigtype(key, + options.ca_sign_algorithms)) != 0) { + logit("%s: certificate signature algorithm %s: %s", __func__, + (key->cert == NULL || key->cert->signature_type == NULL) ? + "(null)" : key->cert->signature_type, ssh_err(r)); + goto done; + } + key_s = format_key(key); + if (sshkey_is_cert(key)) + ca_s = format_key(key->cert->signature_key); + + if (have_sig) { + debug3("%s: have %s signature for %s%s%s", + __func__, pkalg, key_s, + ca_s == NULL ? "" : " CA ", + ca_s == NULL ? "" : ca_s); + if ((r = sshpkt_get_string(ssh, &sig, &slen)) != 0 || + (r = sshpkt_get_end(ssh)) != 0) + fatal("%s: %s", __func__, ssh_err(r)); + if ((b = sshbuf_new()) == NULL) + fatal("%s: sshbuf_new failed", __func__); + if (ssh->compat & SSH_OLD_SESSIONID) { + if ((r = sshbuf_put(b, session_id2, + session_id2_len)) != 0) + fatal("%s: sshbuf_put session id: %s", + __func__, ssh_err(r)); + } else { + if ((r = sshbuf_put_string(b, session_id2, + session_id2_len)) != 0) + fatal("%s: sshbuf_put_string session id: %s", + __func__, ssh_err(r)); + } + if (!authctxt->valid || authctxt->user == NULL) { + debug2("%s: disabled because of invalid user", + __func__); + goto done; + } + /* reconstruct packet */ + xasprintf(&userstyle, "%s%s%s", authctxt->user, + authctxt->style ? ":" : "", + authctxt->style ? authctxt->style : ""); + if ((r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || + (r = sshbuf_put_cstring(b, userstyle)) != 0 || + (r = sshbuf_put_cstring(b, authctxt->service)) != 0 || + (r = sshbuf_put_cstring(b, "publickey")) != 0 || + (r = sshbuf_put_u8(b, have_sig)) != 0 || + (r = sshbuf_put_cstring(b, pkalg)) != 0 || + (r = sshbuf_put_string(b, pkblob, blen)) != 0) + fatal("%s: build packet failed: %s", + __func__, ssh_err(r)); +#ifdef DEBUG_PK + sshbuf_dump(b, stderr); +#endif + /* test for correct signature */ + authenticated = 0; + if (PRIVSEP(user_key_allowed(ssh, pw, key, 1, &authopts)) && + PRIVSEP(sshkey_verify(key, sig, slen, + sshbuf_ptr(b), sshbuf_len(b), + (ssh->compat & SSH_BUG_SIGTYPE) == 0 ? pkalg : NULL, + ssh->compat)) == 0) { + authenticated = 1; + } + auth2_record_key(authctxt, authenticated, key); + } else { + debug("%s: test pkalg %s pkblob %s%s%s", + __func__, pkalg, key_s, + ca_s == NULL ? "" : " CA ", + ca_s == NULL ? "" : ca_s); + + if ((r = sshpkt_get_end(ssh)) != 0) + fatal("%s: %s", __func__, ssh_err(r)); + + if (!authctxt->valid || authctxt->user == NULL) { + debug2("%s: disabled because of invalid user", + __func__); + goto done; + } + /* 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(ssh, pw, key, 0, NULL))) { + if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_PK_OK)) + != 0 || + (r = sshpkt_put_cstring(ssh, pkalg)) != 0 || + (r = sshpkt_put_string(ssh, pkblob, blen)) != 0 || + (r = sshpkt_send(ssh)) != 0 || + (r = ssh_packet_write_wait(ssh)) != 0) + fatal("%s: %s", __func__, ssh_err(r)); + authctxt->postponed = 1; + } + } +done: + if (authenticated == 1 && auth_activate_options(ssh, authopts) != 0) { + debug("%s: key options inconsistent with existing", __func__); + authenticated = 0; + } + debug2("%s: authenticated %d pkalg %s", __func__, authenticated, pkalg); + + sshbuf_free(b); + sshauthopt_free(authopts); + sshkey_free(key); + free(userstyle); + free(pkalg); + free(pkblob); + free(key_s); + free(ca_s); + free(sig); + return authenticated; +} + +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; +} + +/* + * Process a single authorized_principals format line. Returns 0 and sets + * authoptsp is principal is authorised, -1 otherwise. "loc" is used as a + * log preamble for file/line information. + */ +static int +check_principals_line(struct ssh *ssh, char *cp, const struct sshkey_cert *cert, + const char *loc, struct sshauthopt **authoptsp) +{ + u_int i, found = 0; + char *ep, *line_opts; + const char *reason = NULL; + struct sshauthopt *opts = NULL; + + if (authoptsp != NULL) + *authoptsp = NULL; + + /* 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; + } + if ((opts = sshauthopt_parse(line_opts, &reason)) == NULL) { + debug("%s: bad principals options: %s", loc, reason); + auth_debug_add("%s: bad principals options: %s", loc, reason); + return -1; + } + /* Check principals in cert against those on line */ + for (i = 0; i < cert->nprincipals; i++) { + if (strcmp(cp, cert->principals[i]) != 0) + continue; + debug3("%s: matched principal \"%.100s\"", + loc, cert->principals[i]); + found = 1; + } + if (found && authoptsp != NULL) { + *authoptsp = opts; + opts = NULL; + } + sshauthopt_free(opts); + return found ? 0 : -1; +} + +static int +process_principals(struct ssh *ssh, FILE *f, const char *file, + const struct sshkey_cert *cert, struct sshauthopt **authoptsp) +{ + char loc[256], *line = NULL, *cp, *ep; + size_t linesize = 0; + u_long linenum = 0; + u_int found_principal = 0; + + if (authoptsp != NULL) + *authoptsp = NULL; + + while (getline(&line, &linesize, f) != -1) { + linenum++; + /* Always consume entire input */ + if (found_principal) + continue; + + /* 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; + + snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum); + if (check_principals_line(ssh, cp, cert, loc, authoptsp) == 0) + found_principal = 1; + } + free(line); + return found_principal; +} + +/* XXX remove pw args here and elsewhere once ssh->authctxt is guaranteed */ + +static int +match_principals_file(struct ssh *ssh, struct passwd *pw, char *file, + struct sshkey_cert *cert, struct sshauthopt **authoptsp) +{ + FILE *f; + int success; + + if (authoptsp != NULL) + *authoptsp = NULL; + + 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; + } + success = process_principals(ssh, f, file, cert, authoptsp); + fclose(f); + restore_uid(); + return success; +} + +/* + * Checks whether principal is allowed in output of command. + * returns 1 if the principal is allowed or 0 otherwise. + */ +static int +match_principals_command(struct ssh *ssh, struct passwd *user_pw, + const struct sshkey *key, struct sshauthopt **authoptsp) +{ + struct passwd *runas_pw = NULL; + const struct sshkey_cert *cert = key->cert; + FILE *f = NULL; + int r, ok, found_principal = 0; + int i, ac = 0, uid_swapped = 0; + pid_t pid; + char *tmp, *username = NULL, *command = NULL, **av = NULL; + char *ca_fp = NULL, *key_fp = NULL, *catext = NULL, *keytext = NULL; + char serial_s[16], uidstr[32]; + void (*osigchld)(int); + + if (authoptsp != NULL) + *authoptsp = NULL; + if (options.authorized_principals_command == NULL) + return 0; + if (options.authorized_principals_command_user == NULL) { + error("No user for AuthorizedPrincipalsCommand specified, " + "skipping"); + return 0; + } + + /* + * NB. all returns later this function should go via "out" to + * ensure the original SIGCHLD handler is restored properly. + */ + osigchld = signal(SIGCHLD, SIG_DFL); + + /* Prepare and verify the user for the command */ + username = percent_expand(options.authorized_principals_command_user, + "u", user_pw->pw_name, (char *)NULL); + runas_pw = getpwnam(username); + if (runas_pw == NULL) { + error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s", + username, strerror(errno)); + goto out; + } + + /* Turn the command into an argument vector */ + if (argv_split(options.authorized_principals_command, &ac, &av) != 0) { + error("AuthorizedPrincipalsCommand \"%s\" contains " + "invalid quotes", command); + goto out; + } + if (ac == 0) { + error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments", + command); + goto out; + } + if ((ca_fp = sshkey_fingerprint(cert->signature_key, + options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { + error("%s: sshkey_fingerprint failed", __func__); + goto out; + } + if ((key_fp = sshkey_fingerprint(key, + options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { + error("%s: sshkey_fingerprint failed", __func__); + goto out; + } + if ((r = sshkey_to_base64(cert->signature_key, &catext)) != 0) { + error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r)); + goto out; + } + if ((r = sshkey_to_base64(key, &keytext)) != 0) { + error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r)); + goto out; + } + snprintf(serial_s, sizeof(serial_s), "%llu", + (unsigned long long)cert->serial); + snprintf(uidstr, sizeof(uidstr), "%llu", + (unsigned long long)user_pw->pw_uid); + for (i = 1; i < ac; i++) { + tmp = percent_expand(av[i], + "U", uidstr, + "u", user_pw->pw_name, + "h", user_pw->pw_dir, + "t", sshkey_ssh_name(key), + "T", sshkey_ssh_name(cert->signature_key), + "f", key_fp, + "F", ca_fp, + "k", keytext, + "K", catext, + "i", cert->key_id, + "s", serial_s, + (char *)NULL); + if (tmp == NULL) + fatal("%s: percent_expand failed", __func__); + free(av[i]); + av[i] = tmp; + } + /* Prepare a printable command for logs, etc. */ + command = argv_assemble(ac, av); + + if ((pid = subprocess("AuthorizedPrincipalsCommand", runas_pw, command, + ac, av, &f, + SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD)) == 0) + goto out; + + uid_swapped = 1; + temporarily_use_uid(runas_pw); + + ok = process_principals(ssh, f, "(command)", cert, authoptsp); + + fclose(f); + f = NULL; + + if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command, 0) != 0) + goto out; + + /* Read completed successfully */ + found_principal = ok; + out: + if (f != NULL) + fclose(f); + signal(SIGCHLD, osigchld); + for (i = 0; i < ac; i++) + free(av[i]); + free(av); + if (uid_swapped) + restore_uid(); + free(command); + free(username); + free(ca_fp); + free(key_fp); + free(catext); + free(keytext); + return found_principal; +} + +static void +skip_space(char **cpp) +{ + char *cp; + + for (cp = *cpp; *cp == ' ' || *cp == '\t'; cp++) + ; + *cpp = cp; +} + +/* + * Advanced *cpp past the end of key options, defined as the first unquoted + * whitespace character. Returns 0 on success or -1 on failure (e.g. + * unterminated quotes). + */ +static int +advance_past_options(char **cpp) +{ + char *cp = *cpp; + int quoted = 0; + + for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { + if (*cp == '\\' && cp[1] == '"') + cp++; /* Skip both */ + else if (*cp == '"') + quoted = !quoted; + } + *cpp = cp; + /* return failure for unterminated quotes */ + return (*cp == '\0' && quoted) ? -1 : 0; +} + +/* + * Check a single line of an authorized_keys-format file. Returns 0 if key + * matches, -1 otherwise. Will return key/cert options via *authoptsp + * on success. "loc" is used as file/line location in log messages. + */ +static int +check_authkey_line(struct ssh *ssh, struct passwd *pw, struct sshkey *key, + char *cp, const char *loc, struct sshauthopt **authoptsp) +{ + int want_keytype = sshkey_is_cert(key) ? KEY_UNSPEC : key->type; + struct sshkey *found = NULL; + struct sshauthopt *keyopts = NULL, *certopts = NULL, *finalopts = NULL; + char *key_options = NULL, *fp = NULL; + const char *reason = NULL; + int ret = -1; + + if (authoptsp != NULL) + *authoptsp = NULL; + + if ((found = sshkey_new(want_keytype)) == NULL) { + debug3("%s: keytype %d failed", __func__, want_keytype); + goto out; + } + + /* XXX djm: peek at key type in line and skip if unwanted */ + + if (sshkey_read(found, &cp) != 0) { + /* no key? check for options */ + debug2("%s: check options: '%s'", loc, cp); + key_options = cp; + if (advance_past_options(&cp) != 0) { + reason = "invalid key option string"; + goto fail_reason; + } + skip_space(&cp); + if (sshkey_read(found, &cp) != 0) { + /* still no key? advance to next line*/ + debug2("%s: advance: '%s'", loc, cp); + goto out; + } + } + /* Parse key options now; we need to know if this is a CA key */ + if ((keyopts = sshauthopt_parse(key_options, &reason)) == NULL) { + debug("%s: bad key options: %s", loc, reason); + auth_debug_add("%s: bad key options: %s", loc, reason); + goto out; + } + /* Ignore keys that don't match or incorrectly marked as CAs */ + if (sshkey_is_cert(key)) { + /* Certificate; check signature key against CA */ + if (!sshkey_equal(found, key->cert->signature_key) || + !keyopts->cert_authority) + goto out; + } else { + /* Plain key: check it against key found in file */ + if (!sshkey_equal(found, key) || keyopts->cert_authority) + goto out; + } + + /* We have a candidate key, perform authorisation checks */ + if ((fp = sshkey_fingerprint(found, + options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) + fatal("%s: fingerprint failed", __func__); + + debug("%s: matching %s found: %s %s", loc, + sshkey_is_cert(key) ? "CA" : "key", sshkey_type(found), fp); + + if (auth_authorise_keyopts(ssh, pw, keyopts, + sshkey_is_cert(key), loc) != 0) { + reason = "Refused by key options"; + goto fail_reason; + } + /* That's all we need for plain keys. */ + if (!sshkey_is_cert(key)) { + verbose("Accepted key %s %s found at %s", + sshkey_type(found), fp, loc); + finalopts = keyopts; + keyopts = NULL; + goto success; + } + + /* + * Additional authorisation for certificates. + */ + + /* Parse and check options present in certificate */ + if ((certopts = sshauthopt_from_cert(key)) == NULL) { + reason = "Invalid certificate options"; + goto fail_reason; + } + if (auth_authorise_keyopts(ssh, pw, certopts, 0, loc) != 0) { + reason = "Refused by certificate options"; + goto fail_reason; + } + if ((finalopts = sshauthopt_merge(keyopts, certopts, &reason)) == NULL) + goto fail_reason; + + /* + * 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 (keyopts->cert_principals != NULL && + !match_principals_option(keyopts->cert_principals, key->cert)) { + reason = "Certificate does not contain an authorized principal"; + goto fail_reason; + } + if (sshkey_cert_check_authority(key, 0, 0, + keyopts->cert_principals == NULL ? pw->pw_name : NULL, &reason) != 0) + goto fail_reason; + + verbose("Accepted certificate ID \"%s\" (serial %llu) " + "signed by CA %s %s found at %s", + key->cert->key_id, + (unsigned long long)key->cert->serial, + sshkey_type(found), fp, loc); + + success: + if (finalopts == NULL) + fatal("%s: internal error: missing options", __func__); + if (authoptsp != NULL) { + *authoptsp = finalopts; + finalopts = NULL; + } + /* success */ + ret = 0; + goto out; + + fail_reason: + error("%s", reason); + auth_debug_add("%s", reason); + out: + free(fp); + sshauthopt_free(keyopts); + sshauthopt_free(certopts); + sshauthopt_free(finalopts); + sshkey_free(found); + return ret; +} + +/* + * 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(struct ssh *ssh, struct passwd *pw, FILE *f, + char *file, struct sshkey *key, struct sshauthopt **authoptsp) +{ + char *cp, *line = NULL, loc[256]; + size_t linesize = 0; + int found_key = 0; + u_long linenum = 0; + + if (authoptsp != NULL) + *authoptsp = NULL; + + while (getline(&line, &linesize, f) != -1) { + linenum++; + /* Always consume entire file */ + if (found_key) + continue; + + /* Skip leading whitespace, empty and comment lines. */ + cp = line; + skip_space(&cp); + if (!*cp || *cp == '\n' || *cp == '#') + continue; + snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum); + if (check_authkey_line(ssh, pw, key, cp, loc, authoptsp) == 0) + found_key = 1; + } + free(line); + return found_key; +} + +/* Authenticate a certificate key against TrustedUserCAKeys */ +static int +user_cert_trusted_ca(struct ssh *ssh, struct passwd *pw, struct sshkey *key, + struct sshauthopt **authoptsp) +{ + char *ca_fp, *principals_file = NULL; + const char *reason; + struct sshauthopt *principals_opts = NULL, *cert_opts = NULL; + struct sshauthopt *final_opts = NULL; + int r, ret = 0, found_principal = 0, use_authorized_principals; + + if (authoptsp != NULL) + *authoptsp = NULL; + + if (!sshkey_is_cert(key) || options.trusted_user_ca_keys == NULL) + return 0; + + if ((ca_fp = sshkey_fingerprint(key->cert->signature_key, + options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) + return 0; + + if ((r = sshkey_in_file(key->cert->signature_key, + options.trusted_user_ca_keys, 1, 0)) != 0) { + debug2("%s: CA %s %s is not listed in %s: %s", __func__, + sshkey_type(key->cert->signature_key), ca_fp, + options.trusted_user_ca_keys, ssh_err(r)); + 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(ssh, pw, principals_file, + key->cert, &principals_opts)) + found_principal = 1; + } + /* Try querying command if specified */ + if (!found_principal && match_principals_command(ssh, pw, key, + &principals_opts)) + found_principal = 1; + /* If principals file or command is specified, then require a match */ + use_authorized_principals = principals_file != NULL || + options.authorized_principals_command != NULL; + if (!found_principal && use_authorized_principals) { + reason = "Certificate does not contain an authorized principal"; + goto fail_reason; + } + if (use_authorized_principals && principals_opts == NULL) + fatal("%s: internal error: missing principals_opts", __func__); + if (sshkey_cert_check_authority(key, 0, 1, + use_authorized_principals ? NULL : pw->pw_name, &reason) != 0) + goto fail_reason; + + /* Check authority from options in key and from principals file/cmd */ + if ((cert_opts = sshauthopt_from_cert(key)) == NULL) { + reason = "Invalid certificate options"; + goto fail_reason; + } + if (auth_authorise_keyopts(ssh, pw, cert_opts, 0, "cert") != 0) { + reason = "Refused by certificate options"; + goto fail_reason; + } + if (principals_opts == NULL) { + final_opts = cert_opts; + cert_opts = NULL; + } else { + if (auth_authorise_keyopts(ssh, pw, principals_opts, 0, + "principals") != 0) { + reason = "Refused by certificate principals options"; + goto fail_reason; + } + if ((final_opts = sshauthopt_merge(principals_opts, + cert_opts, &reason)) == NULL) { + fail_reason: + error("%s", reason); + auth_debug_add("%s", reason); + goto out; + } + } + + /* Success */ + verbose("Accepted certificate ID \"%s\" (serial %llu) signed by " + "%s CA %s via %s", key->cert->key_id, + (unsigned long long)key->cert->serial, + sshkey_type(key->cert->signature_key), ca_fp, + options.trusted_user_ca_keys); + if (authoptsp != NULL) { + *authoptsp = final_opts; + final_opts = NULL; + } + ret = 1; + out: + sshauthopt_free(principals_opts); + sshauthopt_free(cert_opts); + sshauthopt_free(final_opts); + 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 ssh *ssh, struct passwd *pw, struct sshkey *key, + char *file, struct sshauthopt **authoptsp) +{ + FILE *f; + int found_key = 0; + + if (authoptsp != NULL) + *authoptsp = NULL; + + /* 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(ssh, pw, f, file, + key, authoptsp); + 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 ssh *ssh, struct passwd *user_pw, + struct sshkey *key, struct sshauthopt **authoptsp) +{ + struct passwd *runas_pw = NULL; + FILE *f = NULL; + int r, ok, found_key = 0; + int i, uid_swapped = 0, ac = 0; + pid_t pid; + char *username = NULL, *key_fp = NULL, *keytext = NULL; + char uidstr[32], *tmp, *command = NULL, **av = NULL; + void (*osigchld)(int); + + if (authoptsp != NULL) + *authoptsp = NULL; + if (options.authorized_keys_command == NULL) + return 0; + if (options.authorized_keys_command_user == NULL) { + error("No user for AuthorizedKeysCommand specified, skipping"); + return 0; + } + + /* + * NB. all returns later this function should go via "out" to + * ensure the original SIGCHLD handler is restored properly. + */ + osigchld = signal(SIGCHLD, SIG_DFL); + + /* Prepare and verify the user for the command */ + username = percent_expand(options.authorized_keys_command_user, + "u", user_pw->pw_name, (char *)NULL); + runas_pw = getpwnam(username); + if (runas_pw == NULL) { + error("AuthorizedKeysCommandUser \"%s\" not found: %s", + username, strerror(errno)); + goto out; + } + + /* Prepare AuthorizedKeysCommand */ + if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash, + SSH_FP_DEFAULT)) == NULL) { + error("%s: sshkey_fingerprint failed", __func__); + goto out; + } + if ((r = sshkey_to_base64(key, &keytext)) != 0) { + error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r)); + goto out; + } + + /* Turn the command into an argument vector */ + if (argv_split(options.authorized_keys_command, &ac, &av) != 0) { + error("AuthorizedKeysCommand \"%s\" contains invalid quotes", + command); + goto out; + } + if (ac == 0) { + error("AuthorizedKeysCommand \"%s\" yielded no arguments", + command); + goto out; + } + snprintf(uidstr, sizeof(uidstr), "%llu", + (unsigned long long)user_pw->pw_uid); + for (i = 1; i < ac; i++) { + tmp = percent_expand(av[i], + "U", uidstr, + "u", user_pw->pw_name, + "h", user_pw->pw_dir, + "t", sshkey_ssh_name(key), + "f", key_fp, + "k", keytext, + (char *)NULL); + if (tmp == NULL) + fatal("%s: percent_expand failed", __func__); + free(av[i]); + av[i] = tmp; + } + /* Prepare a printable command for logs, etc. */ + command = argv_assemble(ac, av); + + /* + * If AuthorizedKeysCommand was run without arguments + * then fall back to the old behaviour of passing the + * target username as a single argument. + */ + if (ac == 1) { + av = xreallocarray(av, ac + 2, sizeof(*av)); + av[1] = xstrdup(user_pw->pw_name); + av[2] = NULL; + /* Fix up command too, since it is used in log messages */ + free(command); + xasprintf(&command, "%s %s", av[0], av[1]); + } + + if ((pid = subprocess("AuthorizedKeysCommand", runas_pw, command, + ac, av, &f, + SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD)) == 0) + goto out; + + uid_swapped = 1; + temporarily_use_uid(runas_pw); + + ok = check_authkeys_file(ssh, user_pw, f, + options.authorized_keys_command, key, authoptsp); + + fclose(f); + f = NULL; + + if (exited_cleanly(pid, "AuthorizedKeysCommand", command, 0) != 0) + goto out; + + /* Read completed successfully */ + found_key = ok; + out: + if (f != NULL) + fclose(f); + signal(SIGCHLD, osigchld); + for (i = 0; i < ac; i++) + free(av[i]); + free(av); + if (uid_swapped) + restore_uid(); + free(command); + free(username); + free(key_fp); + free(keytext); + return found_key; +} + +/* + * Check whether key authenticates and authorises the user. + */ +int +user_key_allowed(struct ssh *ssh, struct passwd *pw, struct sshkey *key, + int auth_attempt, struct sshauthopt **authoptsp) +{ + u_int success, i; + char *file; + struct sshauthopt *opts = NULL; + if (authoptsp != NULL) + *authoptsp = NULL; + + if (auth_key_is_revoked(key)) + return 0; + if (sshkey_is_cert(key) && + auth_key_is_revoked(key->cert->signature_key)) + return 0; + + if ((success = user_cert_trusted_ca(ssh, pw, key, &opts)) != 0) + goto out; + sshauthopt_free(opts); + opts = NULL; + + if ((success = user_key_command_allowed2(ssh, pw, key, &opts)) != 0) + goto out; + sshauthopt_free(opts); + opts = NULL; + + 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(ssh, pw, key, file, &opts); + free(file); + } + + out: + if (success && authoptsp != NULL) { + *authoptsp = opts; + opts = NULL; + } + sshauthopt_free(opts); + return success; +} + +Authmethod method_pubkey = { + "publickey", + userauth_pubkey, + &options.pubkey_authentication +}; |