/* $OpenBSD: auth.c,v 1.116 2016/08/13 17:47:41 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 #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "xmalloc.h" #include "match.h" #include "groupaccess.h" #include "log.h" #include "buffer.h" #include "misc.h" #include "servconf.h" #include "key.h" #include "hostfile.h" #include "auth.h" #include "auth-options.h" #include "canohost.h" #include "uidswap.h" #include "packet.h" #ifdef GSSAPI #include "ssh-gss.h" #endif #include "authfile.h" #include "monitor_wrap.h" #include "authfile.h" #include "ssherr.h" #include "compat.h" /* import */ extern ServerOptions options; extern int use_privsep; /* Debugging messages */ Buffer auth_debug; int auth_debug_init; /* * Check if the user is allowed to log in via ssh. If user is listed * in DenyUsers or one of user's groups is listed in DenyGroups, false * will be returned. If AllowUsers isn't empty and user isn't listed * there, or if AllowGroups isn't empty and one of user's groups isn't * listed there, false will be returned. * If the user's shell is not executable, false will be returned. * Otherwise true is returned. */ int allowed_user(struct passwd * pw) { struct ssh *ssh = active_state; /* XXX */ struct stat st; const char *hostname = NULL, *ipaddr = NULL; u_int i; /* Shouldn't be called if pw is NULL, but better safe than sorry... */ if (!pw || !pw->pw_name) return 0; /* * Deny if shell does not exist or is not executable unless we * are chrooting. */ if (options.chroot_directory == NULL || strcasecmp(options.chroot_directory, "none") == 0) { char *shell = xstrdup((pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell); /* empty = /bin/sh */ if (stat(shell, &st) != 0) { logit("User %.100s not allowed because shell %.100s " "does not exist", pw->pw_name, shell); free(shell); return 0; } if (S_ISREG(st.st_mode) == 0 || (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) { logit("User %.100s not allowed because shell %.100s " "is not executable", pw->pw_name, shell); free(shell); return 0; } free(shell); } if (options.num_deny_users > 0 || options.num_allow_users > 0 || options.num_deny_groups > 0 || options.num_allow_groups > 0) { hostname = auth_get_canonical_hostname(ssh, options.use_dns); ipaddr = ssh_remote_ipaddr(ssh); } /* Return false if user is listed in DenyUsers */ if (options.num_deny_users > 0) { for (i = 0; i < options.num_deny_users; i++) if (match_user(pw->pw_name, hostname, ipaddr, options.deny_users[i])) { logit("User %.100s from %.100s not allowed " "because listed in DenyUsers", pw->pw_name, hostname); return 0; } } /* Return false if AllowUsers isn't empty and user isn't listed there */ if (options.num_allow_users > 0) { for (i = 0; i < options.num_allow_users; i++) if (match_user(pw->pw_name, hostname, ipaddr, options.allow_users[i])) break; /* i < options.num_allow_users iff we break for loop */ if (i >= options.num_allow_users) { logit("User %.100s from %.100s not allowed because " "not listed in AllowUsers", pw->pw_name, hostname); return 0; } } if (options.num_deny_groups > 0 || options.num_allow_groups > 0) { /* Get the user's group access list (primary and supplementary) */ if (ga_init(pw->pw_name, pw->pw_gid) == 0) { logit("User %.100s from %.100s not allowed because " "not in any group", pw->pw_name, hostname); return 0; } /* Return false if one of user's groups is listed in DenyGroups */ if (options.num_deny_groups > 0) if (ga_match(options.deny_groups, options.num_deny_groups)) { ga_free(); logit("User %.100s from %.100s not allowed " "because a group is listed in DenyGroups", pw->pw_name, hostname); return 0; } /* * Return false if AllowGroups isn't empty and one of user's groups * isn't listed there */ if (options.num_allow_groups > 0) if (!ga_match(options.allow_groups, options.num_allow_groups)) { ga_free(); logit("User %.100s from %.100s not allowed " "because none of user's groups are listed " "in AllowGroups", pw->pw_name, hostname); return 0; } ga_free(); } /* We found no reason not to let this user try to log on... */ return 1; } void auth_info(Authctxt *authctxt, const char *fmt, ...) { va_list ap; int i; free(authctxt->info); authctxt->info = NULL; va_start(ap, fmt); i = vasprintf(&authctxt->info, fmt, ap); va_end(ap); if (i < 0 || authctxt->info == NULL) fatal("vasprintf failed"); } void auth_log(Authctxt *authctxt, int authenticated, int partial, const char *method, const char *submethod) { struct ssh *ssh = active_state; /* XXX */ void (*authlog) (const char *fmt,...) = verbose; char *authmsg; if (use_privsep && !mm_is_monitor() && !authctxt->postponed) return; /* Raise logging level */ if (authenticated == 1 || !authctxt->valid || authctxt->failures >= options.max_authtries / 2 || strcmp(method, "password") == 0) authlog = logit; if (authctxt->postponed) authmsg = "Postponed"; else if (partial) authmsg = "Partial"; else authmsg = authenticated ? "Accepted" : "Failed"; authlog("%s %s%s%s for %s%.100s from %.200s port %d ssh2%s%s", authmsg, method, submethod != NULL ? "/" : "", submethod == NULL ? "" : submethod, authctxt->valid ? "" : "invalid user ", authctxt->user, ssh_remote_ipaddr(ssh), ssh_remote_port(ssh), authctxt->info != NULL ? ": " : "", authctxt->info != NULL ? authctxt->info : ""); free(authctxt->info); authctxt->info = NULL; } void auth_maxtries_exceeded(Authctxt *authctxt) { struct ssh *ssh = active_state; /* XXX */ error("maximum authentication attempts exceeded for " "%s%.100s from %.200s port %d ssh2", authctxt->valid ? "" : "invalid user ", authctxt->user, ssh_remote_ipaddr(ssh), ssh_remote_port(ssh)); packet_disconnect("Too many authentication failures"); /* NOTREACHED */ } /* * Check whether root logins are disallowed. */ int auth_root_allowed(const char *method) { struct ssh *ssh = active_state; /* XXX */ switch (options.permit_root_login) { case PERMIT_YES: return 1; case PERMIT_NO_PASSWD: if (strcmp(method, "publickey") == 0 || strcmp(method, "hostbased") == 0 || strcmp(method, "gssapi-with-mic") == 0) return 1; break; case PERMIT_FORCED_ONLY: if (forced_command) { logit("Root login accepted for forced command."); return 1; } break; } logit("ROOT LOGIN REFUSED FROM %.200s port %d", ssh_remote_ipaddr(ssh), ssh_remote_port(ssh)); return 0; } /* * Given a template and a passwd structure, build a filename * by substituting % tokenised options. Currently, %% becomes '%', * %h becomes the home directory and %u the username. * * This returns a buffer allocated by xmalloc. */ char * expand_authorized_keys(const char *filename, struct passwd *pw) { char *file, ret[PATH_MAX]; int i; file = percent_expand(filename, "h", pw->pw_dir, "u", pw->pw_name, (char *)NULL); /* * Ensure that filename starts anchored. If not, be backward * compatible and prepend the '%h/' */ if (*file == '/') return (file); i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file); if (i < 0 || (size_t)i >= sizeof(ret)) fatal("expand_authorized_keys: path too long"); free(file); return (xstrdup(ret)); } char * authorized_principals_file(struct passwd *pw) { if (options.authorized_principals_file == NULL) return NULL; return expand_authorized_keys(options.authorized_principals_file, pw); } /* return ok if key exists in sysfile or userfile */ HostStatus check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host, const char *sysfile, const char *userfile) { char *user_hostfile; struct stat st; HostStatus host_status; struct hostkeys *hostkeys; const struct hostkey_entry *found; hostkeys = init_hostkeys(); load_hostkeys(hostkeys, host, sysfile); if (userfile != NULL) { user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); if (options.strict_modes && (stat(user_hostfile, &st) == 0) && ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || (st.st_mode & 022) != 0)) { logit("Authentication refused for %.100s: " "bad owner or modes for %.200s", pw->pw_name, user_hostfile); auth_debug_add("Ignored %.200s: bad ownership or modes", user_hostfile); } else { temporarily_use_uid(pw); load_hostkeys(hostkeys, host, user_hostfile); restore_uid(); } free(user_hostfile); } host_status = check_key_in_hostkeys(hostkeys, key, &found); if (host_status == HOST_REVOKED) error("WARNING: revoked key for %s attempted authentication", found->host); else if (host_status == HOST_OK) debug("%s: key for %s found at %s:%ld", __func__, found->host, found->file, found->line); else debug("%s: key for host %s not found", __func__, host); free_hostkeys(hostkeys); return host_status; } /* * Check a given path for security. This is defined as all components * of the path to the file must be owned by either the owner of * of the file or root and no directories must be group or world writable. * * XXX Should any specific check be done for sym links ? * * Takes a file name, its stat information (preferably from fstat() to * avoid races), the uid of the expected owner, their home directory and an * error buffer plus max size as arguments. * * Returns 0 on success and -1 on failure */ int auth_secure_path(const char *name, struct stat *stp, const char *pw_dir, uid_t uid, char *err, size_t errlen) { char buf[PATH_MAX], homedir[PATH_MAX]; char *cp; int comparehome = 0; struct stat st; if (realpath(name, buf) == NULL) { snprintf(err, errlen, "realpath %s failed: %s", name, strerror(errno)); return -1; } if (pw_dir != NULL && realpath(pw_dir, homedir) != NULL) comparehome = 1; if (!S_ISREG(stp->st_mode)) { snprintf(err, errlen, "%s is not a regular file", buf); return -1; } if ((stp->st_uid != 0 && stp->st_uid != uid) || (stp->st_mode & 022) != 0) { snprintf(err, errlen, "bad ownership or modes for file %s", buf); return -1; } /* for each component of the canonical path, walking upwards */ for (;;) { if ((cp = dirname(buf)) == NULL) { snprintf(err, errlen, "dirname() failed"); return -1; } strlcpy(buf, cp, sizeof(buf)); if (stat(buf, &st) < 0 || (st.st_uid != 0 && st.st_uid != uid) || (st.st_mode & 022) != 0) { snprintf(err, errlen, "bad ownership or modes for directory %s", buf); return -1; } /* If are past the homedir then we can stop */ if (comparehome && strcmp(homedir, buf) == 0) break; /* * dirname should always complete with a "/" path, * but we can be paranoid and check for "." too */ if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) break; } return 0; } /* * Version of secure_path() that accepts an open file descriptor to * avoid races. * * Returns 0 on success and -1 on failure */ static int secure_filename(FILE *f, const char *file, struct passwd *pw, char *err, size_t errlen) { struct stat st; /* check the open file to avoid races */ if (fstat(fileno(f), &st) < 0) { snprintf(err, errlen, "cannot stat file %s: %s", file, strerror(errno)); return -1; } return auth_secure_path(file, &st, pw->pw_dir, pw->pw_uid, err, errlen); } static FILE * auth_openfile(const char *file, struct passwd *pw, int strict_modes, int log_missing, char *file_type) { char line[1024]; struct stat st; int fd; FILE *f; if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1) { if (log_missing || errno != ENOENT) debug("Could not open %s '%s': %s", file_type, file, strerror(errno)); return NULL; } if (fstat(fd, &st) < 0) { close(fd); return NULL; } if (!S_ISREG(st.st_mode)) { logit("User %s %s %s is not a regular file", pw->pw_name, file_type, file); close(fd); return NULL; } unset_nonblock(fd); if ((f = fdopen(fd, "r")) == NULL) { close(fd); return NULL; } if (strict_modes && secure_filename(f, file, pw, line, sizeof(line)) != 0) { fclose(f); logit("Authentication refused: %s", line); auth_debug_add("Ignored %s: %s", file_type, line); return NULL; } return f; } FILE * auth_openkeyfile(const char *file, struct passwd *pw, int strict_modes) { return auth_openfile(file, pw, strict_modes, 1, "authorized keys"); } FILE * auth_openprincipals(const char *file, struct passwd *pw, int strict_modes) { return auth_openfile(file, pw, strict_modes, 0, "authorized principals"); } struct passwd * getpwnamallow(const char *user) { struct ssh *ssh = active_state; /* XXX */ extern login_cap_t *lc; auth_session_t *as; struct passwd *pw; struct connection_info *ci = get_connection_info(1, options.use_dns); ci->user = user; parse_server_match_config(&options, ci); pw = getpwnam(user); if (pw == NULL) { logit("Invalid user %.100s from %.100s port %d", user, ssh_remote_ipaddr(ssh), ssh_remote_port(ssh)); return (NULL); } if (!allowed_user(pw)) return (NULL); if ((lc = login_getclass(pw->pw_class)) == NULL) { debug("unable to get login class: %s", user); return (NULL); } if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { debug("Approval failure for %s", user); pw = NULL; } if (as != NULL) auth_close(as); if (pw != NULL) return (pwcopy(pw)); return (NULL); } /* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */ int auth_key_is_revoked(Key *key) { char *fp = NULL; int r; if (options.revoked_keys_file == NULL) return 0; if ((fp = sshkey_fingerprint(key, options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { r = SSH_ERR_ALLOC_FAIL; error("%s: fingerprint key: %s", __func__, ssh_err(r)); goto out; } r = sshkey_check_revoked(key, options.revoked_keys_file); switch (r) { case 0: break; /* not revoked */ case SSH_ERR_KEY_REVOKED: error("Authentication key %s %s revoked by file %s", sshkey_type(key), fp, options.revoked_keys_file); goto out; default: error("Error checking authentication key %s %s in " "revoked keys file %s: %s", sshkey_type(key), fp, options.revoked_keys_file, ssh_err(r)); goto out; } /* Success */ r = 0; out: free(fp); return r == 0 ? 0 : 1; } void auth_debug_add(const char *fmt,...) { char buf[1024]; va_list args; if (!auth_debug_init) return; va_start(args, fmt); vsnprintf(buf, sizeof(buf), fmt, args); va_end(args); buffer_put_cstring(&auth_debug, buf); } void auth_debug_send(void) { char *msg; if (!auth_debug_init) return; while (buffer_len(&auth_debug)) { msg = buffer_get_string(&auth_debug, NULL); packet_send_debug("%s", msg); free(msg); } } void auth_debug_reset(void) { if (auth_debug_init) buffer_clear(&auth_debug); else { buffer_init(&auth_debug); auth_debug_init = 1; } } struct passwd * fakepw(void) { static struct passwd fake; memset(&fake, 0, sizeof(fake)); fake.pw_name = "NOUSER"; fake.pw_passwd = "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; fake.pw_gecos = "NOUSER"; fake.pw_uid = (uid_t)-1; fake.pw_gid = (gid_t)-1; fake.pw_class = ""; fake.pw_dir = "/nonexist"; fake.pw_shell = "/nonexist"; return (&fake); } /* * Returns the remote DNS hostname as a string. The returned string must not * be freed. NB. this will usually trigger a DNS query the first time it is * called. * This function does additional checks on the hostname to mitigate some * attacks on legacy rhosts-style authentication. * XXX is RhostsRSAAuthentication vulnerable to these? * XXX Can we remove these checks? (or if not, remove RhostsRSAAuthentication?) */ static char * remote_hostname(struct ssh *ssh) { struct sockaddr_storage from; socklen_t fromlen; struct addrinfo hints, *ai, *aitop; char name[NI_MAXHOST], ntop2[NI_MAXHOST]; const char *ntop = ssh_remote_ipaddr(ssh); /* Get IP address of client. */ fromlen = sizeof(from); memset(&from, 0, sizeof(from)); if (getpeername(ssh_packet_get_connection_in(ssh), (struct sockaddr *)&from, &fromlen) < 0) { debug("getpeername failed: %.100s", strerror(errno)); return strdup(ntop); } debug3("Trying to reverse map address %.100s.", ntop); /* Map the IP address to a host name. */ if (getnameinfo((struct sockaddr *)&from, fromlen, name, sizeof(name), NULL, 0, NI_NAMEREQD) != 0) { /* Host name not found. Use ip address. */ return strdup(ntop); } /* * if reverse lookup result looks like a numeric hostname, * someone is trying to trick us by PTR record like following: * 1.1.1.10.in-addr.arpa. IN PTR 2.3.4.5 */ memset(&hints, 0, sizeof(hints)); hints.ai_socktype = SOCK_DGRAM; /*dummy*/ hints.ai_flags = AI_NUMERICHOST; if (getaddrinfo(name, NULL, &hints, &ai) == 0) { logit("Nasty PTR record \"%s\" is set up for %s, ignoring", name, ntop); freeaddrinfo(ai); return strdup(ntop); } /* Names are stored in lowercase. */ lowercase(name); /* * Map it back to an IP address and check that the given * address actually is an address of this host. This is * necessary because anyone with access to a name server can * define arbitrary names for an IP address. Mapping from * name to IP address can be trusted better (but can still be * fooled if the intruder has access to the name server of * the domain). */ memset(&hints, 0, sizeof(hints)); hints.ai_family = from.ss_family; hints.ai_socktype = SOCK_STREAM; if (getaddrinfo(name, NULL, &hints, &aitop) != 0) { logit("reverse mapping checking getaddrinfo for %.700s " "[%s] failed.", name, ntop); return strdup(ntop); } /* Look for the address from the list of addresses. */ for (ai = aitop; ai; ai = ai->ai_next) { if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop2, sizeof(ntop2), NULL, 0, NI_NUMERICHOST) == 0 && (strcmp(ntop, ntop2) == 0)) break; } freeaddrinfo(aitop); /* If we reached the end of the list, the address was not there. */ if (ai == NULL) { /* Address not found for the host name. */ logit("Address %.100s maps to %.600s, but this does not " "map back to the address.", ntop, name); return strdup(ntop); } return strdup(name); } /* * Return the canonical name of the host in the other side of the current * connection. The host name is cached, so it is efficient to call this * several times. */ const char * auth_get_canonical_hostname(struct ssh *ssh, int use_dns) { static char *dnsname; if (!use_dns) return ssh_remote_ipaddr(ssh); else if (dnsname != NULL) return dnsname; else { dnsname = remote_hostname(ssh); return dnsname; } }