/* $NetBSD: ssh-keysign.c,v 1.17.2.1 2023/12/25 12:31:08 martin Exp $ */ /* $OpenBSD: ssh-keysign.c,v 1.71 2022/08/01 11:09:26 djm Exp $ */ /* * Copyright (c) 2002 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: ssh-keysign.c,v 1.17.2.1 2023/12/25 12:31:08 martin Exp $"); #include #ifdef WITH_OPENSSL #include #endif #include #include #include #include #include #include #include #include #include #include "xmalloc.h" #include "log.h" #include "sshkey.h" #include "ssh.h" #include "ssh2.h" #include "misc.h" #include "sshbuf.h" #include "authfile.h" #include "msg.h" #include "canohost.h" #include "pathnames.h" #include "readconf.h" #include "uidswap.h" #include "ssherr.h" extern char *__progname; static int valid_request(struct passwd *pw, char *host, struct sshkey **ret, char **pkalgp, u_char *data, size_t datalen) { struct sshbuf *b; struct sshkey *key = NULL; u_char type, *pkblob; char *p; size_t blen, len; char *pkalg, *luser; int r, pktype, fail; if (ret != NULL) *ret = NULL; if (pkalgp != NULL) *pkalgp = NULL; fail = 0; if ((b = sshbuf_from(data, datalen)) == NULL) fatal_f("sshbuf_from failed"); /* session id */ if ((r = sshbuf_get_string(b, NULL, &len)) != 0) fatal_fr(r, "parse session ID"); if (len != 20 && /* SHA1 */ len != 32 && /* SHA256 */ len != 48 && /* SHA384 */ len != 64) /* SHA512 */ fail++; if ((r = sshbuf_get_u8(b, &type)) != 0) fatal_fr(r, "parse type"); if (type != SSH2_MSG_USERAUTH_REQUEST) fail++; /* server user */ if ((r = sshbuf_skip_string(b)) != 0) fatal_fr(r, "parse user"); /* service */ if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) fatal_fr(r, "parse service"); if (strcmp("ssh-connection", p) != 0) fail++; free(p); /* method */ if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) fatal_fr(r, "parse method"); if (strcmp("hostbased", p) != 0) fail++; free(p); /* pubkey */ if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 || (r = sshbuf_get_string(b, &pkblob, &blen)) != 0) fatal_fr(r, "parse pk"); pktype = sshkey_type_from_name(pkalg); if (pktype == KEY_UNSPEC) fail++; else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { error_fr(r, "decode key"); fail++; } else if (key->type != pktype) fail++; /* client host name, handle trailing dot */ if ((r = sshbuf_get_cstring(b, &p, &len)) != 0) fatal_fr(r, "parse hostname"); debug2_f("check expect chost %s got %s", host, p); if (strlen(host) != len - 1) fail++; else if (p[len - 1] != '.') fail++; else if (strncasecmp(host, p, len - 1) != 0) fail++; free(p); /* local user */ if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0) fatal_fr(r, "parse luser"); if (strcmp(pw->pw_name, luser) != 0) fail++; free(luser); /* end of message */ if (sshbuf_len(b) != 0) fail++; sshbuf_free(b); debug3_f("fail %d", fail); if (!fail) { if (ret != NULL) { *ret = key; key = NULL; } if (pkalgp != NULL) { *pkalgp = pkalg; pkalg = NULL; } } sshkey_free(key); free(pkalg); free(pkblob); return (fail ? -1 : 0); } int main(int argc, char **argv) { struct sshbuf *b; Options options; #define NUM_KEYTYPES 5 struct sshkey *keys[NUM_KEYTYPES], *key = NULL; struct passwd *pw; int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd; u_char *signature, *data, rver; char *host, *fp, *pkalg; size_t slen, dlen; #ifdef __OpenBSD__ if (pledge("stdio rpath getpw dns id", NULL) != 0) fatal("%s: pledge: %s", __progname, strerror(errno)); #endif /* Ensure that stdin and stdout are connected */ if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2) exit(1); /* Leave /dev/null fd iff it is attached to stderr */ if (fd > 2) close(fd); i = 0; /* XXX This really needs to read sshd_config for the paths */ key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY); key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY); key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY); key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY); key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY); if ((pw = getpwuid(getuid())) == NULL) fatal("getpwuid failed"); pw = pwcopy(pw); permanently_set_uid(pw); #ifdef DEBUG_SSH_KEYSIGN log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0); #endif /* verify that ssh-keysign is enabled by the admin */ initialize_options(&options); (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", &options, 0, NULL); (void)fill_default_options(&options); if (options.enable_ssh_keysign != 1) fatal("ssh-keysign not enabled in %s", _PATH_HOST_CONFIG_FILE); #ifdef __OpenBSD__ if (pledge("stdio dns", NULL) != 0) fatal("%s: pledge: %s", __progname, strerror(errno)); #endif for (i = found = 0; i < NUM_KEYTYPES; i++) { if (key_fd[i] != -1) found = 1; } if (found == 0) fatal("could not open any host key"); #ifdef WITH_OPENSSL OpenSSL_add_all_algorithms(); #endif found = 0; for (i = 0; i < NUM_KEYTYPES; i++) { keys[i] = NULL; if (key_fd[i] == -1) continue; r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC, NULL, &key, NULL); close(key_fd[i]); if (r != 0) debug_r(r, "parse key %d", i); else if (key != NULL) { keys[i] = key; found = 1; } } if (!found) fatal("no hostkey found"); if ((b = sshbuf_new()) == NULL) fatal("%s: sshbuf_new failed", __progname); if (ssh_msg_recv(STDIN_FILENO, b) < 0) fatal("%s: ssh_msg_recv failed", __progname); if ((r = sshbuf_get_u8(b, &rver)) != 0) fatal_r(r, "%s: buffer error", __progname); if (rver != version) fatal("%s: bad version: received %d, expected %d", __progname, rver, version); if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0) fatal_r(r, "%s: buffer error", __progname); if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO) fatal("%s: bad fd = %d", __progname, fd); if ((host = get_local_name(fd)) == NULL) fatal("%s: cannot get local name for fd", __progname); if ((r = sshbuf_get_string(b, &data, &dlen)) != 0) fatal_r(r, "%s: buffer error", __progname); if (valid_request(pw, host, &key, &pkalg, data, dlen) < 0) fatal("%s: not a valid request", __progname); free(host); found = 0; for (i = 0; i < NUM_KEYTYPES; i++) { if (keys[i] != NULL && sshkey_equal_public(key, keys[i])) { found = 1; break; } } if (!found) { if ((fp = sshkey_fingerprint(key, options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) fatal("%s: sshkey_fingerprint failed", __progname); fatal("%s: no matching hostkey found for key %s %s", __progname, sshkey_type(key), fp ? fp : ""); } if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, pkalg, NULL, NULL, 0)) != 0) fatal_r(r, "%s: sshkey_sign failed", __progname); free(data); /* send reply */ sshbuf_reset(b); if ((r = sshbuf_put_string(b, signature, slen)) != 0) fatal_r(r, "%s: buffer error", __progname); if (ssh_msg_send(STDOUT_FILENO, version, b) == -1) fatal("%s: ssh_msg_send failed", __progname); return (0); }