/* $OpenBSD: kex.c,v 1.182 2023/10/11 04:46:29 djm 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 *); 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", }; struct kexalg { char *name; u_int type; int ec_nid; int hash_alg; }; static const struct kexalg kexalgs[] = { #ifdef WITH_OPENSSL { KEX_DH1, KEX_DH_GRP1_SHA1, 0, SSH_DIGEST_SHA1 }, { KEX_DH14_SHA1, KEX_DH_GRP14_SHA1, 0, SSH_DIGEST_SHA1 }, { KEX_DH14_SHA256, KEX_DH_GRP14_SHA256, 0, SSH_DIGEST_SHA256 }, { KEX_DH16_SHA512, KEX_DH_GRP16_SHA512, 0, SSH_DIGEST_SHA512 }, { KEX_DH18_SHA512, KEX_DH_GRP18_SHA512, 0, SSH_DIGEST_SHA512 }, { KEX_DHGEX_SHA1, KEX_DH_GEX_SHA1, 0, SSH_DIGEST_SHA1 }, #ifdef HAVE_EVP_SHA256 { KEX_DHGEX_SHA256, KEX_DH_GEX_SHA256, 0, SSH_DIGEST_SHA256 }, #endif /* HAVE_EVP_SHA256 */ #ifdef OPENSSL_HAS_ECC { KEX_ECDH_SHA2_NISTP256, KEX_ECDH_SHA2, NID_X9_62_prime256v1, SSH_DIGEST_SHA256 }, { KEX_ECDH_SHA2_NISTP384, KEX_ECDH_SHA2, NID_secp384r1, SSH_DIGEST_SHA384 }, # ifdef OPENSSL_HAS_NISTP521 { KEX_ECDH_SHA2_NISTP521, KEX_ECDH_SHA2, NID_secp521r1, SSH_DIGEST_SHA512 }, # endif /* OPENSSL_HAS_NISTP521 */ #endif /* OPENSSL_HAS_ECC */ #endif /* WITH_OPENSSL */ #if defined(HAVE_EVP_SHA256) || !defined(WITH_OPENSSL) { KEX_CURVE25519_SHA256, KEX_C25519_SHA256, 0, SSH_DIGEST_SHA256 }, { KEX_CURVE25519_SHA256_OLD, KEX_C25519_SHA256, 0, SSH_DIGEST_SHA256 }, #ifdef USE_SNTRUP761X25519 { KEX_SNTRUP761X25519_SHA512, KEX_KEM_SNTRUP761X25519_SHA512, 0, SSH_DIGEST_SHA512 }, #endif #endif /* HAVE_EVP_SHA256 || !WITH_OPENSSL */ { NULL, 0, -1, -1}, }; char * kex_alg_list(char sep) { char *ret = NULL, *tmp; size_t nlen, rlen = 0; const struct kexalg *k; for (k = kexalgs; k->name != NULL; k++) { if (ret != NULL) ret[rlen++] = sep; nlen = strlen(k->name); if ((tmp = realloc(ret, rlen + nlen + 2)) == NULL) { free(ret); return NULL; } ret = tmp; memcpy(ret + rlen, k->name, nlen + 1); rlen += nlen; } return ret; } static const struct kexalg * kex_alg_by_name(const char *name) { const struct kexalg *k; for (k = kexalgs; k->name != NULL; k++) { if (strcmp(k->name, name) == 0) return k; } return NULL; } /* Validate KEX method name list */ int kex_names_valid(const char *names) { char *s, *cp, *p; if (names == NULL || strcmp(names, "") == 0) return 0; if ((s = cp = strdup(names)) == NULL) return 0; for ((p = strsep(&cp, ",")); p && *p != '\0'; (p = strsep(&cp, ","))) { if (kex_alg_by_name(p) == NULL) { error("Unsupported KEX algorithm \"%.100s\"", p); free(s); return 0; } } debug3("kex names ok: [%s]", names); free(s); return 1; } /* * Concatenate algorithm names, avoiding duplicates in the process. * Caller must free returned string. */ char * kex_names_cat(const char *a, const char *b) { char *ret = NULL, *tmp = NULL, *cp, *p, *m; size_t len; if (a == NULL || *a == '\0') return strdup(b); if (b == NULL || *b == '\0') return strdup(a); if (strlen(b) > 1024*1024) return NULL; len = strlen(a) + strlen(b) + 2; if ((tmp = cp = strdup(b)) == NULL || (ret = calloc(1, len)) == NULL) { free(tmp); return NULL; } strlcpy(ret, a, len); for ((p = strsep(&cp, ",")); p && *p != '\0'; (p = strsep(&cp, ","))) { if ((m = match_list(ret, p, NULL)) != NULL) { free(m); continue; /* Algorithm already present */ } if (strlcat(ret, ",", len) >= len || strlcat(ret, p, len) >= len) { free(tmp); free(ret); return NULL; /* Shouldn't happen */ } } free(tmp); return ret; } /* * Assemble a list of algorithms from a default list and a string from a * configuration file. The user-provided string may begin with '+' to * indicate that it should be appended to the default, '-' that the * specified names should be removed, or '^' that they should be placed * at the head. */ int kex_assemble_names(char **listp, const char *def, const char *all) { char *cp, *tmp, *patterns; char *list = NULL, *ret = NULL, *matching = NULL, *opatterns = NULL; int r = SSH_ERR_INTERNAL_ERROR; if (listp == NULL || def == NULL || all == NULL) return SSH_ERR_INVALID_ARGUMENT; if (*listp == NULL || **listp == '\0') { if ((*listp = strdup(def)) == NULL) return SSH_ERR_ALLOC_FAIL; return 0; } list = *listp; *listp = NULL; if (*list == '+') { /* Append names to default list */ if ((tmp = kex_names_cat(def, list + 1)) == NULL) { r = SSH_ERR_ALLOC_FAIL; goto fail; } free(list); list = tmp; } else if (*list == '-') { /* Remove names from default list */ if ((*listp = match_filter_denylist(def, list + 1)) == NULL) { r = SSH_ERR_ALLOC_FAIL; goto fail; } free(list); /* filtering has already been done */ return 0; } else if (*list == '^') { /* Place names at head of default list */ if ((tmp = kex_names_cat(list + 1, def)) == NULL) { r = SSH_ERR_ALLOC_FAIL; goto fail; } free(list); list = tmp; } else { /* Explicit list, overrides default - just use "list" as is */ } /* * The supplied names may be a pattern-list. For the -list case, * the patterns are applied above. For the +list and explicit list * cases we need to do it now. */ ret = NULL; if ((patterns = opatterns = strdup(list)) == NULL) { r = SSH_ERR_ALLOC_FAIL; goto fail; } /* Apply positive (i.e. non-negated) patterns from the list */ while ((cp = strsep(&patterns, ",")) != NULL) { if (*cp == '!') { /* negated matches are not supported here */ r = SSH_ERR_INVALID_ARGUMENT; goto fail; } free(matching); if ((matching = match_filter_allowlist(all, cp)) == NULL) { r = SSH_ERR_ALLOC_FAIL; goto fail; } if ((tmp = kex_names_cat(ret, matching)) == NULL) { r = SSH_ERR_ALLOC_FAIL; goto fail; } free(ret); ret = tmp; } if (ret == NULL || *ret == '\0') { /* An empty name-list is an error */ /* XXX better error code? */ r = SSH_ERR_INVALID_ARGUMENT; goto fail; } /* success */ *listp = ret; ret = NULL; r = 0; fail: free(matching); free(opatterns); free(list); free(ret); return r; } /* * 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; if (prop == NULL) fatal_f("proposal missing"); for (i = 0; i < PROPOSAL_MAX; i++) { switch(i) { case PROPOSAL_KEX_ALGS: prop[i] = compat_kex_proposal(ssh, kexalgos ? kexalgos : defprop[i]); 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]); } } } 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; error("kex protocol error: type %d 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); } static int kex_send_ext_info(struct ssh *ssh) { int r; char *algs; debug("Sending SSH2_MSG_EXT_INFO"); if ((algs = sshkey_alg_list(0, 1, 1, ',')) == NULL) return SSH_ERR_ALLOC_FAIL; /* XXX filter algs list by allowed pubkey/hostbased types */ if ((r = sshpkt_start(ssh, SSH2_MSG_EXT_INFO)) != 0 || (r = sshpkt_put_u32(ssh, 3)) != 0 || (r = sshpkt_put_cstring(ssh, "server-sig-algs")) != 0 || (r = sshpkt_put_cstring(ssh, algs)) != 0 || (r = sshpkt_put_cstring(ssh, "publickey-hostbound@openssh.com")) != 0 || (r = sshpkt_put_cstring(ssh, "0")) != 0 || (r = sshpkt_put_cstring(ssh, "ping@openssh.com")) != 0 || (r = sshpkt_put_cstring(ssh, "0")) != 0 || (r = sshpkt_send(ssh)) != 0) { error_fr(r, "compose"); goto out; } /* success */ r = 0; out: free(algs); return r; } 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 (ssh->kex->ext_info_c && (ssh->kex->flags & KEX_INITIAL) != 0) if ((r = kex_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; } int kex_input_ext_info(int type, u_int32_t seq, struct ssh *ssh) { struct kex *kex = ssh->kex; u_int32_t i, ninfo; char *name; u_char *val; size_t vlen; int r; debug("SSH2_MSG_EXT_INFO received"); 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 SSH_ERR_INVALID_FORMAT; } 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; } if (strcmp(name, "server-sig-algs") == 0) { /* Ensure no \0 lurking in value */ if (memchr(val, '\0', vlen) != NULL) { error_f("nul byte in %s", name); free(name); free(val); return SSH_ERR_INVALID_FORMAT; } debug_f("%s=<%s>", name, val); kex->server_sig_algs = val; val = NULL; } else if (strcmp(name, "publickey-hostbound@openssh.com") == 0) { if ((r = kex_ext_info_check_ver(kex, name, val, vlen, "0", KEX_HAS_PUBKEY_HOSTBOUND)) != 0) { free(name); free(val); return r; } } else if (strcmp(name, "ping@openssh.com") == 0) { if ((r = kex_ext_info_check_ver(kex, name, val, vlen, "0", KEX_HAS_PING)) != 0) { free(name); free(val); return r; } } else debug_f("%s (unrecognised)", name); 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; debug("SSH2_MSG_NEWKEYS received"); 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; kex->done = 1; kex->flags &= ~KEX_INITIAL; sshbuf_reset(kex->peer); /* sshbuf_reset(kex->my); */ 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, NULL); 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)) != 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 if (strcmp(name, "zlib") == 0) { comp->type = COMP_ZLIB; } 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) { const struct kexalg *kexalg; 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 ((kexalg = kex_alg_by_name(k->name)) == NULL) { error_f("unsupported KEX method %s", k->name); return SSH_ERR_INTERNAL_ERROR; } k->kex_type = kexalg->type; k->hash_alg = kexalg->hash_alg; k->ec_nid = kexalg->ec_nid; 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); } /* returns non-zero if proposal contains any algorithm from algs */ static int has_any_alg(const char *proposal, const char *algs) { char *cp; if ((cp = match_list(proposal, algs, NULL)) == NULL) return 0; free(cp); return 1; } static int kex_choose_conf(struct ssh *ssh) { 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 client supports ext_info_c */ if (kex->server && (kex->flags & KEX_INITIAL)) { char *ext; ext = match_list("ext-info-c", peer[PROPOSAL_KEX_ALGS], NULL); kex->ext_info_c = (ext != NULL); free(ext); } /* Check whether client supports rsa-sha2 algorithms */ if (kex->server && (kex->flags & KEX_INITIAL)) { if (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 (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; }