/* $OpenBSD: kex.c,v 1.187 2024/08/23 04:51:00 deraadt Exp $ */ /* * Copyright (c) 2000, 2001 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 #ifdef HAVE_POLL_H #include #endif #ifdef WITH_OPENSSL #include #include #endif #include "ssh.h" #include "ssh2.h" #include "atomicio.h" #include "version.h" #include "packet.h" #include "compat.h" #include "cipher.h" #include "sshkey.h" #include "kex.h" #include "log.h" #include "mac.h" #include "match.h" #include "misc.h" #include "dispatch.h" #include "monitor.h" #include "myproposal.h" #include "ssherr.h" #include "sshbuf.h" #include "digest.h" #include "xmalloc.h" /* prototype */ static int kex_choose_conf(struct ssh *, uint32_t seq); static int kex_input_newkeys(int, u_int32_t, struct ssh *); static const char * const proposal_names[PROPOSAL_MAX] = { "KEX algorithms", "host key algorithms", "ciphers ctos", "ciphers stoc", "MACs ctos", "MACs stoc", "compression ctos", "compression stoc", "languages ctos", "languages stoc", }; /* * Fill out a proposal array with dynamically allocated values, which may * be modified as required for compatibility reasons. * Any of the options may be NULL, in which case the default is used. * Array contents must be freed by calling kex_proposal_free_entries. */ void kex_proposal_populate_entries(struct ssh *ssh, char *prop[PROPOSAL_MAX], const char *kexalgos, const char *ciphers, const char *macs, const char *comp, const char *hkalgs) { const char *defpropserver[PROPOSAL_MAX] = { KEX_SERVER }; const char *defpropclient[PROPOSAL_MAX] = { KEX_CLIENT }; const char **defprop = ssh->kex->server ? defpropserver : defpropclient; u_int i; char *cp; if (prop == NULL) fatal_f("proposal missing"); /* Append EXT_INFO signalling to KexAlgorithms */ if (kexalgos == NULL) kexalgos = defprop[PROPOSAL_KEX_ALGS]; if ((cp = kex_names_cat(kexalgos, ssh->kex->server ? "ext-info-s,kex-strict-s-v00@openssh.com" : "ext-info-c,kex-strict-c-v00@openssh.com")) == NULL) fatal_f("kex_names_cat"); for (i = 0; i < PROPOSAL_MAX; i++) { switch(i) { case PROPOSAL_KEX_ALGS: prop[i] = compat_kex_proposal(ssh, cp); break; case PROPOSAL_ENC_ALGS_CTOS: case PROPOSAL_ENC_ALGS_STOC: prop[i] = xstrdup(ciphers ? ciphers : defprop[i]); break; case PROPOSAL_MAC_ALGS_CTOS: case PROPOSAL_MAC_ALGS_STOC: prop[i] = xstrdup(macs ? macs : defprop[i]); break; case PROPOSAL_COMP_ALGS_CTOS: case PROPOSAL_COMP_ALGS_STOC: prop[i] = xstrdup(comp ? comp : defprop[i]); break; case PROPOSAL_SERVER_HOST_KEY_ALGS: prop[i] = xstrdup(hkalgs ? hkalgs : defprop[i]); break; default: prop[i] = xstrdup(defprop[i]); } } free(cp); } void kex_proposal_free_entries(char *prop[PROPOSAL_MAX]) { u_int i; for (i = 0; i < PROPOSAL_MAX; i++) free(prop[i]); } /* put algorithm proposal into buffer */ int kex_prop2buf(struct sshbuf *b, char *proposal[PROPOSAL_MAX]) { u_int i; int r; sshbuf_reset(b); /* * add a dummy cookie, the cookie will be overwritten by * kex_send_kexinit(), each time a kexinit is set */ for (i = 0; i < KEX_COOKIE_LEN; i++) { if ((r = sshbuf_put_u8(b, 0)) != 0) return r; } for (i = 0; i < PROPOSAL_MAX; i++) { if ((r = sshbuf_put_cstring(b, proposal[i])) != 0) return r; } if ((r = sshbuf_put_u8(b, 0)) != 0 || /* first_kex_packet_follows */ (r = sshbuf_put_u32(b, 0)) != 0) /* uint32 reserved */ return r; return 0; } /* parse buffer and return algorithm proposal */ int kex_buf2prop(struct sshbuf *raw, int *first_kex_follows, char ***propp) { struct sshbuf *b = NULL; u_char v; u_int i; char **proposal = NULL; int r; *propp = NULL; if ((proposal = calloc(PROPOSAL_MAX, sizeof(char *))) == NULL) return SSH_ERR_ALLOC_FAIL; if ((b = sshbuf_fromb(raw)) == NULL) { r = SSH_ERR_ALLOC_FAIL; goto out; } if ((r = sshbuf_consume(b, KEX_COOKIE_LEN)) != 0) { /* skip cookie */ error_fr(r, "consume cookie"); goto out; } /* extract kex init proposal strings */ for (i = 0; i < PROPOSAL_MAX; i++) { if ((r = sshbuf_get_cstring(b, &(proposal[i]), NULL)) != 0) { error_fr(r, "parse proposal %u", i); goto out; } debug2("%s: %s", proposal_names[i], proposal[i]); } /* first kex follows / reserved */ if ((r = sshbuf_get_u8(b, &v)) != 0 || /* first_kex_follows */ (r = sshbuf_get_u32(b, &i)) != 0) { /* reserved */ error_fr(r, "parse"); goto out; } if (first_kex_follows != NULL) *first_kex_follows = v; debug2("first_kex_follows %d ", v); debug2("reserved %u ", i); r = 0; *propp = proposal; out: if (r != 0 && proposal != NULL) kex_prop_free(proposal); sshbuf_free(b); return r; } void kex_prop_free(char **proposal) { u_int i; if (proposal == NULL) return; for (i = 0; i < PROPOSAL_MAX; i++) free(proposal[i]); free(proposal); } int kex_protocol_error(int type, u_int32_t seq, struct ssh *ssh) { int r; /* If in strict mode, any unexpected message is an error */ if ((ssh->kex->flags & KEX_INITIAL) && ssh->kex->kex_strict) { ssh_packet_disconnect(ssh, "strict KEX violation: " "unexpected packet type %u (seqnr %u)", type, seq); } error_f("type %u seq %u", type, seq); if ((r = sshpkt_start(ssh, SSH2_MSG_UNIMPLEMENTED)) != 0 || (r = sshpkt_put_u32(ssh, seq)) != 0 || (r = sshpkt_send(ssh)) != 0) return r; return 0; } static void kex_reset_dispatch(struct ssh *ssh) { ssh_dispatch_range(ssh, SSH2_MSG_TRANSPORT_MIN, SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); } void kex_set_server_sig_algs(struct ssh *ssh, const char *allowed_algs) { char *alg, *oalgs, *algs, *sigalgs; const char *sigalg; /* * NB. allowed algorithms may contain certificate algorithms that * map to a specific plain signature type, e.g. * rsa-sha2-512-cert-v01@openssh.com => rsa-sha2-512 * We need to be careful here to match these, retain the mapping * and only add each signature algorithm once. */ if ((sigalgs = sshkey_alg_list(0, 1, 1, ',')) == NULL) fatal_f("sshkey_alg_list failed"); oalgs = algs = xstrdup(allowed_algs); free(ssh->kex->server_sig_algs); ssh->kex->server_sig_algs = NULL; for ((alg = strsep(&algs, ",")); alg != NULL && *alg != '\0'; (alg = strsep(&algs, ","))) { if ((sigalg = sshkey_sigalg_by_name(alg)) == NULL) continue; if (!kex_has_any_alg(sigalg, sigalgs)) continue; /* Don't add an algorithm twice. */ if (ssh->kex->server_sig_algs != NULL && kex_has_any_alg(sigalg, ssh->kex->server_sig_algs)) continue; xextendf(&ssh->kex->server_sig_algs, ",", "%s", sigalg); } free(oalgs); free(sigalgs); if (ssh->kex->server_sig_algs == NULL) ssh->kex->server_sig_algs = xstrdup(""); } static int kex_compose_ext_info_server(struct ssh *ssh, struct sshbuf *m) { int r; if (ssh->kex->server_sig_algs == NULL && (ssh->kex->server_sig_algs = sshkey_alg_list(0, 1, 1, ',')) == NULL) return SSH_ERR_ALLOC_FAIL; if ((r = sshbuf_put_u32(m, 3)) != 0 || (r = sshbuf_put_cstring(m, "server-sig-algs")) != 0 || (r = sshbuf_put_cstring(m, ssh->kex->server_sig_algs)) != 0 || (r = sshbuf_put_cstring(m, "publickey-hostbound@openssh.com")) != 0 || (r = sshbuf_put_cstring(m, "0")) != 0 || (r = sshbuf_put_cstring(m, "ping@openssh.com")) != 0 || (r = sshbuf_put_cstring(m, "0")) != 0) { error_fr(r, "compose"); return r; } return 0; } static int kex_compose_ext_info_client(struct ssh *ssh, struct sshbuf *m) { int r; if ((r = sshbuf_put_u32(m, 1)) != 0 || (r = sshbuf_put_cstring(m, "ext-info-in-auth@openssh.com")) != 0 || (r = sshbuf_put_cstring(m, "0")) != 0) { error_fr(r, "compose"); goto out; } /* success */ r = 0; out: return r; } static int kex_maybe_send_ext_info(struct ssh *ssh) { int r; struct sshbuf *m = NULL; if ((ssh->kex->flags & KEX_INITIAL) == 0) return 0; if (!ssh->kex->ext_info_c && !ssh->kex->ext_info_s) return 0; /* Compose EXT_INFO packet. */ if ((m = sshbuf_new()) == NULL) fatal_f("sshbuf_new failed"); if (ssh->kex->ext_info_c && (r = kex_compose_ext_info_server(ssh, m)) != 0) goto fail; if (ssh->kex->ext_info_s && (r = kex_compose_ext_info_client(ssh, m)) != 0) goto fail; /* Send the actual KEX_INFO packet */ debug("Sending SSH2_MSG_EXT_INFO"); if ((r = sshpkt_start(ssh, SSH2_MSG_EXT_INFO)) != 0 || (r = sshpkt_putb(ssh, m)) != 0 || (r = sshpkt_send(ssh)) != 0) { error_f("send EXT_INFO"); goto fail; } r = 0; fail: sshbuf_free(m); return r; } int kex_server_update_ext_info(struct ssh *ssh) { int r; if ((ssh->kex->flags & KEX_HAS_EXT_INFO_IN_AUTH) == 0) return 0; debug_f("Sending SSH2_MSG_EXT_INFO"); if ((r = sshpkt_start(ssh, SSH2_MSG_EXT_INFO)) != 0 || (r = sshpkt_put_u32(ssh, 1)) != 0 || (r = sshpkt_put_cstring(ssh, "server-sig-algs")) != 0 || (r = sshpkt_put_cstring(ssh, ssh->kex->server_sig_algs)) != 0 || (r = sshpkt_send(ssh)) != 0) { error_f("send EXT_INFO"); return r; } return 0; } int kex_send_newkeys(struct ssh *ssh) { int r; kex_reset_dispatch(ssh); if ((r = sshpkt_start(ssh, SSH2_MSG_NEWKEYS)) != 0 || (r = sshpkt_send(ssh)) != 0) return r; debug("SSH2_MSG_NEWKEYS sent"); ssh_dispatch_set(ssh, SSH2_MSG_NEWKEYS, &kex_input_newkeys); if ((r = kex_maybe_send_ext_info(ssh)) != 0) return r; debug("expecting SSH2_MSG_NEWKEYS"); return 0; } /* Check whether an ext_info value contains the expected version string */ static int kex_ext_info_check_ver(struct kex *kex, const char *name, const u_char *val, size_t len, const char *want_ver, u_int flag) { if (memchr(val, '\0', len) != NULL) { error("SSH2_MSG_EXT_INFO: %s value contains nul byte", name); return SSH_ERR_INVALID_FORMAT; } debug_f("%s=<%s>", name, val); if (strcmp(val, want_ver) == 0) kex->flags |= flag; else debug_f("unsupported version of %s extension", name); return 0; } static int kex_ext_info_client_parse(struct ssh *ssh, const char *name, const u_char *value, size_t vlen) { int r; /* NB. some messages are only accepted in the initial EXT_INFO */ if (strcmp(name, "server-sig-algs") == 0) { /* Ensure no \0 lurking in value */ if (memchr(value, '\0', vlen) != NULL) { error_f("nul byte in %s", name); return SSH_ERR_INVALID_FORMAT; } debug_f("%s=<%s>", name, value); free(ssh->kex->server_sig_algs); ssh->kex->server_sig_algs = xstrdup((const char *)value); } else if (ssh->kex->ext_info_received == 1 && strcmp(name, "publickey-hostbound@openssh.com") == 0) { if ((r = kex_ext_info_check_ver(ssh->kex, name, value, vlen, "0", KEX_HAS_PUBKEY_HOSTBOUND)) != 0) { return r; } } else if (ssh->kex->ext_info_received == 1 && strcmp(name, "ping@openssh.com") == 0) { if ((r = kex_ext_info_check_ver(ssh->kex, name, value, vlen, "0", KEX_HAS_PING)) != 0) { return r; } } else debug_f("%s (unrecognised)", name); return 0; } static int kex_ext_info_server_parse(struct ssh *ssh, const char *name, const u_char *value, size_t vlen) { int r; if (strcmp(name, "ext-info-in-auth@openssh.com") == 0) { if ((r = kex_ext_info_check_ver(ssh->kex, name, value, vlen, "0", KEX_HAS_EXT_INFO_IN_AUTH)) != 0) { return r; } } else debug_f("%s (unrecognised)", name); return 0; } int kex_input_ext_info(int type, u_int32_t seq, struct ssh *ssh) { struct kex *kex = ssh->kex; const int max_ext_info = kex->server ? 1 : 2; u_int32_t i, ninfo; char *name; u_char *val; size_t vlen; int r; debug("SSH2_MSG_EXT_INFO received"); if (++kex->ext_info_received > max_ext_info) { error("too many SSH2_MSG_EXT_INFO messages sent by peer"); return dispatch_protocol_error(type, seq, ssh); } ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, &kex_protocol_error); if ((r = sshpkt_get_u32(ssh, &ninfo)) != 0) return r; if (ninfo >= 1024) { error("SSH2_MSG_EXT_INFO with too many entries, expected " "<=1024, received %u", ninfo); return dispatch_protocol_error(type, seq, ssh); } for (i = 0; i < ninfo; i++) { if ((r = sshpkt_get_cstring(ssh, &name, NULL)) != 0) return r; if ((r = sshpkt_get_string(ssh, &val, &vlen)) != 0) { free(name); return r; } debug3_f("extension %s", name); if (kex->server) { if ((r = kex_ext_info_server_parse(ssh, name, val, vlen)) != 0) return r; } else { if ((r = kex_ext_info_client_parse(ssh, name, val, vlen)) != 0) return r; } free(name); free(val); } return sshpkt_get_end(ssh); } static int kex_input_newkeys(int type, u_int32_t seq, struct ssh *ssh) { struct kex *kex = ssh->kex; int r, initial = (kex->flags & KEX_INITIAL) != 0; char *cp, **prop; debug("SSH2_MSG_NEWKEYS received"); if (kex->ext_info_c && initial) ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, &kex_input_ext_info); ssh_dispatch_set(ssh, SSH2_MSG_NEWKEYS, &kex_protocol_error); ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, &kex_input_kexinit); if ((r = sshpkt_get_end(ssh)) != 0) return r; if ((r = ssh_set_newkeys(ssh, MODE_IN)) != 0) return r; if (initial) { /* Remove initial KEX signalling from proposal for rekeying */ if ((r = kex_buf2prop(kex->my, NULL, &prop)) != 0) return r; if ((cp = match_filter_denylist(prop[PROPOSAL_KEX_ALGS], kex->server ? "ext-info-s,kex-strict-s-v00@openssh.com" : "ext-info-c,kex-strict-c-v00@openssh.com")) == NULL) { error_f("match_filter_denylist failed"); goto fail; } free(prop[PROPOSAL_KEX_ALGS]); prop[PROPOSAL_KEX_ALGS] = cp; if ((r = kex_prop2buf(ssh->kex->my, prop)) != 0) { error_f("kex_prop2buf failed"); fail: kex_proposal_free_entries(prop); free(prop); return SSH_ERR_INTERNAL_ERROR; } kex_proposal_free_entries(prop); free(prop); } kex->done = 1; kex->flags &= ~KEX_INITIAL; sshbuf_reset(kex->peer); kex->flags &= ~KEX_INIT_SENT; free(kex->name); kex->name = NULL; return 0; } int kex_send_kexinit(struct ssh *ssh) { u_char *cookie; struct kex *kex = ssh->kex; int r; if (kex == NULL) { error_f("no kex"); return SSH_ERR_INTERNAL_ERROR; } if (kex->flags & KEX_INIT_SENT) return 0; kex->done = 0; /* generate a random cookie */ if (sshbuf_len(kex->my) < KEX_COOKIE_LEN) { error_f("bad kex length: %zu < %d", sshbuf_len(kex->my), KEX_COOKIE_LEN); return SSH_ERR_INVALID_FORMAT; } if ((cookie = sshbuf_mutable_ptr(kex->my)) == NULL) { error_f("buffer error"); return SSH_ERR_INTERNAL_ERROR; } arc4random_buf(cookie, KEX_COOKIE_LEN); if ((r = sshpkt_start(ssh, SSH2_MSG_KEXINIT)) != 0 || (r = sshpkt_putb(ssh, kex->my)) != 0 || (r = sshpkt_send(ssh)) != 0) { error_fr(r, "compose reply"); return r; } debug("SSH2_MSG_KEXINIT sent"); kex->flags |= KEX_INIT_SENT; return 0; } int kex_input_kexinit(int type, u_int32_t seq, struct ssh *ssh) { struct kex *kex = ssh->kex; const u_char *ptr; u_int i; size_t dlen; int r; debug("SSH2_MSG_KEXINIT received"); if (kex == NULL) { error_f("no kex"); return SSH_ERR_INTERNAL_ERROR; } ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, &kex_protocol_error); ptr = sshpkt_ptr(ssh, &dlen); if ((r = sshbuf_put(kex->peer, ptr, dlen)) != 0) return r; /* discard packet */ for (i = 0; i < KEX_COOKIE_LEN; i++) { if ((r = sshpkt_get_u8(ssh, NULL)) != 0) { error_fr(r, "discard cookie"); return r; } } for (i = 0; i < PROPOSAL_MAX; i++) { if ((r = sshpkt_get_string(ssh, NULL, NULL)) != 0) { error_fr(r, "discard proposal"); return r; } } /* * XXX RFC4253 sec 7: "each side MAY guess" - currently no supported * KEX method has the server move first, but a server might be using * a custom method or one that we otherwise don't support. We should * be prepared to remember first_kex_follows here so we can eat a * packet later. * XXX2 - RFC4253 is kind of ambiguous on what first_kex_follows means * for cases where the server *doesn't* go first. I guess we should * ignore it when it is set for these cases, which is what we do now. */ if ((r = sshpkt_get_u8(ssh, NULL)) != 0 || /* first_kex_follows */ (r = sshpkt_get_u32(ssh, NULL)) != 0 || /* reserved */ (r = sshpkt_get_end(ssh)) != 0) return r; if (!(kex->flags & KEX_INIT_SENT)) if ((r = kex_send_kexinit(ssh)) != 0) return r; if ((r = kex_choose_conf(ssh, seq)) != 0) return r; if (kex->kex_type < KEX_MAX && kex->kex[kex->kex_type] != NULL) return (kex->kex[kex->kex_type])(ssh); error_f("unknown kex type %u", kex->kex_type); return SSH_ERR_INTERNAL_ERROR; } struct kex * kex_new(void) { struct kex *kex; if ((kex = calloc(1, sizeof(*kex))) == NULL || (kex->peer = sshbuf_new()) == NULL || (kex->my = sshbuf_new()) == NULL || (kex->client_version = sshbuf_new()) == NULL || (kex->server_version = sshbuf_new()) == NULL || (kex->session_id = sshbuf_new()) == NULL) { kex_free(kex); return NULL; } return kex; } void kex_free_newkeys(struct newkeys *newkeys) { if (newkeys == NULL) return; if (newkeys->enc.key) { explicit_bzero(newkeys->enc.key, newkeys->enc.key_len); free(newkeys->enc.key); newkeys->enc.key = NULL; } if (newkeys->enc.iv) { explicit_bzero(newkeys->enc.iv, newkeys->enc.iv_len); free(newkeys->enc.iv); newkeys->enc.iv = NULL; } free(newkeys->enc.name); explicit_bzero(&newkeys->enc, sizeof(newkeys->enc)); free(newkeys->comp.name); explicit_bzero(&newkeys->comp, sizeof(newkeys->comp)); mac_clear(&newkeys->mac); if (newkeys->mac.key) { explicit_bzero(newkeys->mac.key, newkeys->mac.key_len); free(newkeys->mac.key); newkeys->mac.key = NULL; } free(newkeys->mac.name); explicit_bzero(&newkeys->mac, sizeof(newkeys->mac)); freezero(newkeys, sizeof(*newkeys)); } void kex_free(struct kex *kex) { u_int mode; if (kex == NULL) return; #ifdef WITH_OPENSSL DH_free(kex->dh); #ifdef OPENSSL_HAS_ECC EC_KEY_free(kex->ec_client_key); #endif /* OPENSSL_HAS_ECC */ #endif /* WITH_OPENSSL */ for (mode = 0; mode < MODE_MAX; mode++) { kex_free_newkeys(kex->newkeys[mode]); kex->newkeys[mode] = NULL; } sshbuf_free(kex->peer); sshbuf_free(kex->my); sshbuf_free(kex->client_version); sshbuf_free(kex->server_version); sshbuf_free(kex->client_pub); sshbuf_free(kex->session_id); sshbuf_free(kex->initial_sig); sshkey_free(kex->initial_hostkey); free(kex->failed_choice); free(kex->hostkey_alg); free(kex->name); free(kex); } int kex_ready(struct ssh *ssh, char *proposal[PROPOSAL_MAX]) { int r; if ((r = kex_prop2buf(ssh->kex->my, proposal)) != 0) return r; ssh->kex->flags = KEX_INITIAL; kex_reset_dispatch(ssh); ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, &kex_input_kexinit); return 0; } int kex_setup(struct ssh *ssh, char *proposal[PROPOSAL_MAX]) { int r; if ((r = kex_ready(ssh, proposal)) != 0) return r; if ((r = kex_send_kexinit(ssh)) != 0) { /* we start */ kex_free(ssh->kex); ssh->kex = NULL; return r; } return 0; } /* * Request key re-exchange, returns 0 on success or a ssherr.h error * code otherwise. Must not be called if KEX is incomplete or in-progress. */ int kex_start_rekex(struct ssh *ssh) { if (ssh->kex == NULL) { error_f("no kex"); return SSH_ERR_INTERNAL_ERROR; } if (ssh->kex->done == 0) { error_f("requested twice"); return SSH_ERR_INTERNAL_ERROR; } ssh->kex->done = 0; return kex_send_kexinit(ssh); } static int choose_enc(struct sshenc *enc, char *client, char *server) { char *name = match_list(client, server, NULL); if (name == NULL) return SSH_ERR_NO_CIPHER_ALG_MATCH; if ((enc->cipher = cipher_by_name(name)) == NULL) { error_f("unsupported cipher %s", name); free(name); return SSH_ERR_INTERNAL_ERROR; } enc->name = name; enc->enabled = 0; enc->iv = NULL; enc->iv_len = cipher_ivlen(enc->cipher); enc->key = NULL; enc->key_len = cipher_keylen(enc->cipher); enc->block_size = cipher_blocksize(enc->cipher); return 0; } static int choose_mac(struct ssh *ssh, struct sshmac *mac, char *client, char *server) { char *name = match_list(client, server, NULL); if (name == NULL) return SSH_ERR_NO_MAC_ALG_MATCH; if (mac_setup(mac, name) < 0) { error_f("unsupported MAC %s", name); free(name); return SSH_ERR_INTERNAL_ERROR; } mac->name = name; mac->key = NULL; mac->enabled = 0; return 0; } static int choose_comp(struct sshcomp *comp, char *client, char *server) { char *name = match_list(client, server, NULL); if (name == NULL) return SSH_ERR_NO_COMPRESS_ALG_MATCH; #ifdef WITH_ZLIB if (strcmp(name, "zlib@openssh.com") == 0) { comp->type = COMP_DELAYED; } else #endif /* WITH_ZLIB */ if (strcmp(name, "none") == 0) { comp->type = COMP_NONE; } else { error_f("unsupported compression scheme %s", name); free(name); return SSH_ERR_INTERNAL_ERROR; } comp->name = name; return 0; } static int choose_kex(struct kex *k, char *client, char *server) { k->name = match_list(client, server, NULL); debug("kex: algorithm: %s", k->name ? k->name : "(no match)"); if (k->name == NULL) return SSH_ERR_NO_KEX_ALG_MATCH; if (!kex_name_valid(k->name)) { error_f("unsupported KEX method %s", k->name); return SSH_ERR_INTERNAL_ERROR; } k->kex_type = kex_type_from_name(k->name); k->hash_alg = kex_hash_from_name(k->name); k->ec_nid = kex_nid_from_name(k->name); return 0; } static int choose_hostkeyalg(struct kex *k, char *client, char *server) { free(k->hostkey_alg); k->hostkey_alg = match_list(client, server, NULL); debug("kex: host key algorithm: %s", k->hostkey_alg ? k->hostkey_alg : "(no match)"); if (k->hostkey_alg == NULL) return SSH_ERR_NO_HOSTKEY_ALG_MATCH; k->hostkey_type = sshkey_type_from_name(k->hostkey_alg); if (k->hostkey_type == KEY_UNSPEC) { error_f("unsupported hostkey algorithm %s", k->hostkey_alg); return SSH_ERR_INTERNAL_ERROR; } k->hostkey_nid = sshkey_ecdsa_nid_from_name(k->hostkey_alg); return 0; } static int proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) { static int check[] = { PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 }; int *idx; char *p; for (idx = &check[0]; *idx != -1; idx++) { if ((p = strchr(my[*idx], ',')) != NULL) *p = '\0'; if ((p = strchr(peer[*idx], ',')) != NULL) *p = '\0'; if (strcmp(my[*idx], peer[*idx]) != 0) { debug2("proposal mismatch: my %s peer %s", my[*idx], peer[*idx]); return (0); } } debug2("proposals match"); return (1); } static int kexalgs_contains(char **peer, const char *ext) { return kex_has_any_alg(peer[PROPOSAL_KEX_ALGS], ext); } static int kex_choose_conf(struct ssh *ssh, uint32_t seq) { struct kex *kex = ssh->kex; struct newkeys *newkeys; char **my = NULL, **peer = NULL; char **cprop, **sprop; int nenc, nmac, ncomp; u_int mode, ctos, need, dh_need, authlen; int r, first_kex_follows; debug2("local %s KEXINIT proposal", kex->server ? "server" : "client"); if ((r = kex_buf2prop(kex->my, NULL, &my)) != 0) goto out; debug2("peer %s KEXINIT proposal", kex->server ? "client" : "server"); if ((r = kex_buf2prop(kex->peer, &first_kex_follows, &peer)) != 0) goto out; if (kex->server) { cprop=peer; sprop=my; } else { cprop=my; sprop=peer; } /* Check whether peer supports ext_info/kex_strict */ if ((kex->flags & KEX_INITIAL) != 0) { if (kex->server) { kex->ext_info_c = kexalgs_contains(peer, "ext-info-c"); kex->kex_strict = kexalgs_contains(peer, "kex-strict-c-v00@openssh.com"); } else { kex->ext_info_s = kexalgs_contains(peer, "ext-info-s"); kex->kex_strict = kexalgs_contains(peer, "kex-strict-s-v00@openssh.com"); } if (kex->kex_strict) { debug3_f("will use strict KEX ordering"); if (seq != 0) ssh_packet_disconnect(ssh, "strict KEX violation: " "KEXINIT was not the first packet"); } } /* Check whether client supports rsa-sha2 algorithms */ if (kex->server && (kex->flags & KEX_INITIAL)) { if (kex_has_any_alg(peer[PROPOSAL_SERVER_HOST_KEY_ALGS], "rsa-sha2-256,rsa-sha2-256-cert-v01@openssh.com")) kex->flags |= KEX_RSA_SHA2_256_SUPPORTED; if (kex_has_any_alg(peer[PROPOSAL_SERVER_HOST_KEY_ALGS], "rsa-sha2-512,rsa-sha2-512-cert-v01@openssh.com")) kex->flags |= KEX_RSA_SHA2_512_SUPPORTED; } /* Algorithm Negotiation */ if ((r = choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS])) != 0) { kex->failed_choice = peer[PROPOSAL_KEX_ALGS]; peer[PROPOSAL_KEX_ALGS] = NULL; goto out; } if ((r = choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], sprop[PROPOSAL_SERVER_HOST_KEY_ALGS])) != 0) { kex->failed_choice = peer[PROPOSAL_SERVER_HOST_KEY_ALGS]; peer[PROPOSAL_SERVER_HOST_KEY_ALGS] = NULL; goto out; } for (mode = 0; mode < MODE_MAX; mode++) { if ((newkeys = calloc(1, sizeof(*newkeys))) == NULL) { r = SSH_ERR_ALLOC_FAIL; goto out; } kex->newkeys[mode] = newkeys; ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; if ((r = choose_enc(&newkeys->enc, cprop[nenc], sprop[nenc])) != 0) { kex->failed_choice = peer[nenc]; peer[nenc] = NULL; goto out; } authlen = cipher_authlen(newkeys->enc.cipher); /* ignore mac for authenticated encryption */ if (authlen == 0 && (r = choose_mac(ssh, &newkeys->mac, cprop[nmac], sprop[nmac])) != 0) { kex->failed_choice = peer[nmac]; peer[nmac] = NULL; goto out; } if ((r = choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp])) != 0) { kex->failed_choice = peer[ncomp]; peer[ncomp] = NULL; goto out; } debug("kex: %s cipher: %s MAC: %s compression: %s", ctos ? "client->server" : "server->client", newkeys->enc.name, authlen == 0 ? newkeys->mac.name : "", newkeys->comp.name); } need = dh_need = 0; for (mode = 0; mode < MODE_MAX; mode++) { newkeys = kex->newkeys[mode]; need = MAXIMUM(need, newkeys->enc.key_len); need = MAXIMUM(need, newkeys->enc.block_size); need = MAXIMUM(need, newkeys->enc.iv_len); need = MAXIMUM(need, newkeys->mac.key_len); dh_need = MAXIMUM(dh_need, cipher_seclen(newkeys->enc.cipher)); dh_need = MAXIMUM(dh_need, newkeys->enc.block_size); dh_need = MAXIMUM(dh_need, newkeys->enc.iv_len); dh_need = MAXIMUM(dh_need, newkeys->mac.key_len); } /* XXX need runden? */ kex->we_need = need; kex->dh_need = dh_need; /* ignore the next message if the proposals do not match */ if (first_kex_follows && !proposals_match(my, peer)) ssh->dispatch_skip_packets = 1; r = 0; out: kex_prop_free(my); kex_prop_free(peer); return r; } static int derive_key(struct ssh *ssh, int id, u_int need, u_char *hash, u_int hashlen, const struct sshbuf *shared_secret, u_char **keyp) { struct kex *kex = ssh->kex; struct ssh_digest_ctx *hashctx = NULL; char c = id; u_int have; size_t mdsz; u_char *digest; int r; if ((mdsz = ssh_digest_bytes(kex->hash_alg)) == 0) return SSH_ERR_INVALID_ARGUMENT; if ((digest = calloc(1, ROUNDUP(need, mdsz))) == NULL) { r = SSH_ERR_ALLOC_FAIL; goto out; } /* K1 = HASH(K || H || "A" || session_id) */ if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL || ssh_digest_update_buffer(hashctx, shared_secret) != 0 || ssh_digest_update(hashctx, hash, hashlen) != 0 || ssh_digest_update(hashctx, &c, 1) != 0 || ssh_digest_update_buffer(hashctx, kex->session_id) != 0 || ssh_digest_final(hashctx, digest, mdsz) != 0) { r = SSH_ERR_LIBCRYPTO_ERROR; error_f("KEX hash failed"); goto out; } ssh_digest_free(hashctx); hashctx = NULL; /* * expand key: * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) * Key = K1 || K2 || ... || Kn */ for (have = mdsz; need > have; have += mdsz) { if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL || ssh_digest_update_buffer(hashctx, shared_secret) != 0 || ssh_digest_update(hashctx, hash, hashlen) != 0 || ssh_digest_update(hashctx, digest, have) != 0 || ssh_digest_final(hashctx, digest + have, mdsz) != 0) { error_f("KDF failed"); r = SSH_ERR_LIBCRYPTO_ERROR; goto out; } ssh_digest_free(hashctx); hashctx = NULL; } #ifdef DEBUG_KEX fprintf(stderr, "key '%c'== ", c); dump_digest("key", digest, need); #endif *keyp = digest; digest = NULL; r = 0; out: free(digest); ssh_digest_free(hashctx); return r; } #define NKEYS 6 int kex_derive_keys(struct ssh *ssh, u_char *hash, u_int hashlen, const struct sshbuf *shared_secret) { struct kex *kex = ssh->kex; u_char *keys[NKEYS]; u_int i, j, mode, ctos; int r; /* save initial hash as session id */ if ((kex->flags & KEX_INITIAL) != 0) { if (sshbuf_len(kex->session_id) != 0) { error_f("already have session ID at kex"); return SSH_ERR_INTERNAL_ERROR; } if ((r = sshbuf_put(kex->session_id, hash, hashlen)) != 0) return r; } else if (sshbuf_len(kex->session_id) == 0) { error_f("no session ID in rekex"); return SSH_ERR_INTERNAL_ERROR; } for (i = 0; i < NKEYS; i++) { if ((r = derive_key(ssh, 'A'+i, kex->we_need, hash, hashlen, shared_secret, &keys[i])) != 0) { for (j = 0; j < i; j++) free(keys[j]); return r; } } for (mode = 0; mode < MODE_MAX; mode++) { ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); kex->newkeys[mode]->enc.iv = keys[ctos ? 0 : 1]; kex->newkeys[mode]->enc.key = keys[ctos ? 2 : 3]; kex->newkeys[mode]->mac.key = keys[ctos ? 4 : 5]; } return 0; } int kex_load_hostkey(struct ssh *ssh, struct sshkey **prvp, struct sshkey **pubp) { struct kex *kex = ssh->kex; *pubp = NULL; *prvp = NULL; if (kex->load_host_public_key == NULL || kex->load_host_private_key == NULL) { error_f("missing hostkey loader"); return SSH_ERR_INVALID_ARGUMENT; } *pubp = kex->load_host_public_key(kex->hostkey_type, kex->hostkey_nid, ssh); *prvp = kex->load_host_private_key(kex->hostkey_type, kex->hostkey_nid, ssh); if (*pubp == NULL) return SSH_ERR_NO_HOSTKEY_LOADED; return 0; } int kex_verify_host_key(struct ssh *ssh, struct sshkey *server_host_key) { struct kex *kex = ssh->kex; if (kex->verify_host_key == NULL) { error_f("missing hostkey verifier"); return SSH_ERR_INVALID_ARGUMENT; } if (server_host_key->type != kex->hostkey_type || (kex->hostkey_type == KEY_ECDSA && server_host_key->ecdsa_nid != kex->hostkey_nid)) return SSH_ERR_KEY_TYPE_MISMATCH; if (kex->verify_host_key(server_host_key, ssh) == -1) return SSH_ERR_SIGNATURE_INVALID; return 0; } #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH) void dump_digest(const char *msg, const u_char *digest, int len) { fprintf(stderr, "%s\n", msg); sshbuf_dump_data(digest, len, stderr); } #endif /* * Send a plaintext error message to the peer, suffixed by \r\n. * Only used during banner exchange, and there only for the server. */ static void send_error(struct ssh *ssh, char *msg) { char *crnl = "\r\n"; if (!ssh->kex->server) return; if (atomicio(vwrite, ssh_packet_get_connection_out(ssh), msg, strlen(msg)) != strlen(msg) || atomicio(vwrite, ssh_packet_get_connection_out(ssh), crnl, strlen(crnl)) != strlen(crnl)) error_f("write: %.100s", strerror(errno)); } /* * Sends our identification string and waits for the peer's. Will block for * up to timeout_ms (or indefinitely if timeout_ms <= 0). * Returns on 0 success or a ssherr.h code on failure. */ int kex_exchange_identification(struct ssh *ssh, int timeout_ms, const char *version_addendum) { int remote_major, remote_minor, mismatch, oerrno = 0; size_t len, n; int r, expect_nl; u_char c; struct sshbuf *our_version = ssh->kex->server ? ssh->kex->server_version : ssh->kex->client_version; struct sshbuf *peer_version = ssh->kex->server ? ssh->kex->client_version : ssh->kex->server_version; char *our_version_string = NULL, *peer_version_string = NULL; char *cp, *remote_version = NULL; /* Prepare and send our banner */ sshbuf_reset(our_version); if (version_addendum != NULL && *version_addendum == '\0') version_addendum = NULL; if ((r = sshbuf_putf(our_version, "SSH-%d.%d-%s%s%s\r\n", PROTOCOL_MAJOR_2, PROTOCOL_MINOR_2, SSH_VERSION, version_addendum == NULL ? "" : " ", version_addendum == NULL ? "" : version_addendum)) != 0) { oerrno = errno; error_fr(r, "sshbuf_putf"); goto out; } if (atomicio(vwrite, ssh_packet_get_connection_out(ssh), sshbuf_mutable_ptr(our_version), sshbuf_len(our_version)) != sshbuf_len(our_version)) { oerrno = errno; debug_f("write: %.100s", strerror(errno)); r = SSH_ERR_SYSTEM_ERROR; goto out; } if ((r = sshbuf_consume_end(our_version, 2)) != 0) { /* trim \r\n */ oerrno = errno; error_fr(r, "sshbuf_consume_end"); goto out; } our_version_string = sshbuf_dup_string(our_version); if (our_version_string == NULL) { error_f("sshbuf_dup_string failed"); r = SSH_ERR_ALLOC_FAIL; goto out; } debug("Local version string %.100s", our_version_string); /* Read other side's version identification. */ for (n = 0; ; n++) { if (n >= SSH_MAX_PRE_BANNER_LINES) { send_error(ssh, "No SSH identification string " "received."); error_f("No SSH version received in first %u lines " "from server", SSH_MAX_PRE_BANNER_LINES); r = SSH_ERR_INVALID_FORMAT; goto out; } sshbuf_reset(peer_version); expect_nl = 0; for (;;) { if (timeout_ms > 0) { r = waitrfd(ssh_packet_get_connection_in(ssh), &timeout_ms, NULL); if (r == -1 && errno == ETIMEDOUT) { send_error(ssh, "Timed out waiting " "for SSH identification string."); error("Connection timed out during " "banner exchange"); r = SSH_ERR_CONN_TIMEOUT; goto out; } else if (r == -1) { oerrno = errno; error_f("%s", strerror(errno)); r = SSH_ERR_SYSTEM_ERROR; goto out; } } len = atomicio(read, ssh_packet_get_connection_in(ssh), &c, 1); if (len != 1 && errno == EPIPE) { verbose_f("Connection closed by remote host"); r = SSH_ERR_CONN_CLOSED; goto out; } else if (len != 1) { oerrno = errno; error_f("read: %.100s", strerror(errno)); r = SSH_ERR_SYSTEM_ERROR; goto out; } if (c == '\r') { expect_nl = 1; continue; } if (c == '\n') break; if (c == '\0' || expect_nl) { verbose_f("banner line contains invalid " "characters"); goto invalid; } if ((r = sshbuf_put_u8(peer_version, c)) != 0) { oerrno = errno; error_fr(r, "sshbuf_put"); goto out; } if (sshbuf_len(peer_version) > SSH_MAX_BANNER_LEN) { verbose_f("banner line too long"); goto invalid; } } /* Is this an actual protocol banner? */ if (sshbuf_len(peer_version) > 4 && memcmp(sshbuf_ptr(peer_version), "SSH-", 4) == 0) break; /* If not, then just log the line and continue */ if ((cp = sshbuf_dup_string(peer_version)) == NULL) { error_f("sshbuf_dup_string failed"); r = SSH_ERR_ALLOC_FAIL; goto out; } /* Do not accept lines before the SSH ident from a client */ if (ssh->kex->server) { verbose_f("client sent invalid protocol identifier " "\"%.256s\"", cp); free(cp); goto invalid; } debug_f("banner line %zu: %s", n, cp); free(cp); } peer_version_string = sshbuf_dup_string(peer_version); if (peer_version_string == NULL) fatal_f("sshbuf_dup_string failed"); /* XXX must be same size for sscanf */ if ((remote_version = calloc(1, sshbuf_len(peer_version))) == NULL) { error_f("calloc failed"); r = SSH_ERR_ALLOC_FAIL; goto out; } /* * Check that the versions match. In future this might accept * several versions and set appropriate flags to handle them. */ if (sscanf(peer_version_string, "SSH-%d.%d-%[^\n]\n", &remote_major, &remote_minor, remote_version) != 3) { error("Bad remote protocol version identification: '%.100s'", peer_version_string); invalid: send_error(ssh, "Invalid SSH identification string."); r = SSH_ERR_INVALID_FORMAT; goto out; } debug("Remote protocol version %d.%d, remote software version %.100s", remote_major, remote_minor, remote_version); compat_banner(ssh, remote_version); mismatch = 0; switch (remote_major) { case 2: break; case 1: if (remote_minor != 99) mismatch = 1; break; default: mismatch = 1; break; } if (mismatch) { error("Protocol major versions differ: %d vs. %d", PROTOCOL_MAJOR_2, remote_major); send_error(ssh, "Protocol major versions differ."); r = SSH_ERR_NO_PROTOCOL_VERSION; goto out; } if (ssh->kex->server && (ssh->compat & SSH_BUG_PROBE) != 0) { logit("probed from %s port %d with %s. Don't panic.", ssh_remote_ipaddr(ssh), ssh_remote_port(ssh), peer_version_string); r = SSH_ERR_CONN_CLOSED; /* XXX */ goto out; } if (ssh->kex->server && (ssh->compat & SSH_BUG_SCANNER) != 0) { logit("scanned from %s port %d with %s. Don't panic.", ssh_remote_ipaddr(ssh), ssh_remote_port(ssh), peer_version_string); r = SSH_ERR_CONN_CLOSED; /* XXX */ goto out; } /* success */ r = 0; out: free(our_version_string); free(peer_version_string); free(remote_version); if (r == SSH_ERR_SYSTEM_ERROR) errno = oerrno; return r; }