upstream commit
Revise hostkeys@openssh.com hostkey learning extension.
The client will not ask the server to prove ownership of the private
halves of any hitherto-unseen hostkeys it offers to the client.
Allow UpdateHostKeys option to take an 'ask' argument to let the
user manually review keys offered.
ok markus@
diff --git a/clientloop.c b/clientloop.c
index c6f8e9d..a19d9d0 100644
--- a/clientloop.c
+++ b/clientloop.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: clientloop.c,v 1.268 2015/02/16 22:08:57 djm Exp $ */
+/* $OpenBSD: clientloop.c,v 1.269 2015/02/16 22:13:32 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -2089,6 +2089,216 @@
return 0;
}
+struct hostkeys_update_ctx {
+ /* The hostname and (optionally) IP address string for the server */
+ char *host_str, *ip_str;
+
+ /*
+ * Keys received from the server and a flag for each indicating
+ * whether they already exist in known_hosts.
+ * keys_seen is filled in by hostkeys_find() and later (for new
+ * keys) by client_global_hostkeys_private_confirm().
+ */
+ struct sshkey **keys;
+ int *keys_seen;
+ size_t nkeys;
+
+ size_t nnew;
+
+ /*
+ * Keys that are in known_hosts, but were not present in the update
+ * from the server (i.e. scheduled to be deleted).
+ * Filled in by hostkeys_find().
+ */
+ struct sshkey **old_keys;
+ size_t nold;
+};
+
+static void
+hostkeys_update_ctx_free(struct hostkeys_update_ctx *ctx)
+{
+ size_t i;
+
+ if (ctx == NULL)
+ return;
+ for (i = 0; i < ctx->nkeys; i++)
+ sshkey_free(ctx->keys[i]);
+ free(ctx->keys);
+ free(ctx->keys_seen);
+ for (i = 0; i < ctx->nold; i++)
+ sshkey_free(ctx->old_keys[i]);
+ free(ctx->old_keys);
+ free(ctx->host_str);
+ free(ctx->ip_str);
+ free(ctx);
+}
+
+static int
+hostkeys_find(struct hostkey_foreach_line *l, void *_ctx)
+{
+ struct hostkeys_update_ctx *ctx = (struct hostkeys_update_ctx *)_ctx;
+ size_t i;
+ struct sshkey **tmp;
+
+ if (l->status != HKF_STATUS_MATCHED || l->key == NULL ||
+ l->key->type == KEY_RSA1)
+ return 0;
+
+ /* Mark off keys we've already seen for this host */
+ for (i = 0; i < ctx->nkeys; i++) {
+ if (sshkey_equal(l->key, ctx->keys[i])) {
+ debug3("%s: found %s key at %s:%ld", __func__,
+ sshkey_ssh_name(ctx->keys[i]), l->path, l->linenum);
+ ctx->keys_seen[i] = 1;
+ return 0;
+ }
+ }
+ /* This line contained a key that not offered by the server */
+ debug3("%s: deprecated %s key at %s:%ld", __func__,
+ sshkey_ssh_name(l->key), l->path, l->linenum);
+ if ((tmp = reallocarray(ctx->old_keys, ctx->nold + 1,
+ sizeof(*ctx->old_keys))) == NULL)
+ fatal("%s: reallocarray failed nold = %zu",
+ __func__, ctx->nold);
+ ctx->old_keys = tmp;
+ ctx->old_keys[ctx->nold++] = l->key;
+ l->key = NULL;
+
+ return 0;
+}
+
+static void
+update_known_hosts(struct hostkeys_update_ctx *ctx)
+{
+ int r, loglevel = options.update_hostkeys == SSH_UPDATE_HOSTKEYS_ASK ?
+ SYSLOG_LEVEL_INFO : SYSLOG_LEVEL_VERBOSE;
+ char *fp, *response;
+ size_t i;
+
+ for (i = 0; i < ctx->nkeys; i++) {
+ if (ctx->keys_seen[i] != 2)
+ continue;
+ if ((fp = sshkey_fingerprint(ctx->keys[i],
+ options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
+ fatal("%s: sshkey_fingerprint failed", __func__);
+ do_log2(loglevel, "Learned new hostkey: %s %s",
+ sshkey_type(ctx->keys[i]), fp);
+ free(fp);
+ }
+ for (i = 0; i < ctx->nold; i++) {
+ if ((fp = sshkey_fingerprint(ctx->old_keys[i],
+ options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
+ fatal("%s: sshkey_fingerprint failed", __func__);
+ do_log2(loglevel, "Deprecating obsolete hostkey: %s %s",
+ sshkey_type(ctx->old_keys[i]), fp);
+ free(fp);
+ }
+ if (options.update_hostkeys == SSH_UPDATE_HOSTKEYS_ASK) {
+ leave_raw_mode(options.request_tty == REQUEST_TTY_FORCE);
+ response = NULL;
+ for (i = 0; !quit_pending && i < 3; i++) {
+ free(response);
+ response = read_passphrase("Accept updated hostkeys? "
+ "(yes/no): ", RP_ECHO);
+ if (strcasecmp(response, "yes") == 0)
+ break;
+ else if (quit_pending || response == NULL ||
+ strcasecmp(response, "no") == 0) {
+ options.update_hostkeys = 0;
+ break;
+ } else {
+ do_log2(loglevel, "Please enter "
+ "\"yes\" or \"no\"");
+ }
+ }
+ if (quit_pending || i >= 3 || response == NULL)
+ options.update_hostkeys = 0;
+ free(response);
+ enter_raw_mode(options.request_tty == REQUEST_TTY_FORCE);
+ }
+
+ /*
+ * Now that all the keys are verified, we can go ahead and replace
+ * them in known_hosts (assuming SSH_UPDATE_HOSTKEYS_ASK didn't
+ * cancel the operation).
+ */
+ if (options.update_hostkeys != 0 &&
+ (r = hostfile_replace_entries(options.user_hostfiles[0],
+ ctx->host_str, ctx->ip_str, ctx->keys, ctx->nkeys,
+ options.hash_known_hosts, 0,
+ options.fingerprint_hash)) != 0)
+ error("%s: hostfile_replace_entries failed: %s",
+ __func__, ssh_err(r));
+}
+
+static void
+client_global_hostkeys_private_confirm(int type, u_int32_t seq, void *_ctx)
+{
+ struct ssh *ssh = active_state; /* XXX */
+ struct hostkeys_update_ctx *ctx = (struct hostkeys_update_ctx *)_ctx;
+ size_t i, ndone;
+ struct sshbuf *signdata;
+ int r;
+ const u_char *sig;
+ size_t siglen;
+
+ if (ctx->nnew == 0)
+ fatal("%s: ctx->nnew == 0", __func__); /* sanity */
+ if (type != SSH2_MSG_REQUEST_SUCCESS) {
+ error("Server failed to confirm ownership of "
+ "private host keys");
+ hostkeys_update_ctx_free(ctx);
+ return;
+ }
+ if ((signdata = sshbuf_new()) == NULL)
+ fatal("%s: sshbuf_new failed", __func__);
+ /* Don't want to accidentally accept an unbound signature */
+ if (ssh->kex->session_id_len == 0)
+ fatal("%s: ssh->kex->session_id_len == 0", __func__);
+ /*
+ * Expect a signature for each of the ctx->nnew private keys we
+ * haven't seen before. They will be in the same order as the
+ * ctx->keys where the corresponding ctx->keys_seen[i] == 0.
+ */
+ for (ndone = i = 0; i < ctx->nkeys; i++) {
+ if (ctx->keys_seen[i])
+ continue;
+ /* Prepare data to be signed: session ID, unique string, key */
+ sshbuf_reset(signdata);
+ if ((r = sshbuf_put_string(signdata, ssh->kex->session_id,
+ ssh->kex->session_id_len)) != 0 ||
+ (r = sshbuf_put_cstring(signdata,
+ "hostkeys-prove@openssh.com")) != 0 ||
+ (r = sshkey_puts(ctx->keys[i], signdata)) != 0)
+ fatal("%s: failed to prepare signature: %s",
+ __func__, ssh_err(r));
+ /* Extract and verify signature */
+ if ((r = sshpkt_get_string_direct(ssh, &sig, &siglen)) != 0) {
+ error("%s: couldn't parse message: %s",
+ __func__, ssh_err(r));
+ goto out;
+ }
+ if ((r = sshkey_verify(ctx->keys[i], sig, siglen,
+ sshbuf_ptr(signdata), sshbuf_len(signdata), 0)) != 0) {
+ error("%s: server gave bad signature for %s key %zu",
+ __func__, sshkey_type(ctx->keys[i]), i);
+ goto out;
+ }
+ /* Key is good. Mark it as 'seen' */
+ ctx->keys_seen[i] = 2;
+ ndone++;
+ }
+ if (ndone != ctx->nnew)
+ fatal("%s: ndone != ctx->nnew (%zu / %zu)", __func__,
+ ndone, ctx->nnew); /* Shouldn't happen */
+ ssh_packet_check_eom(ssh);
+
+ /* Make the edits to known_hosts */
+ update_known_hosts(ctx);
+ out:
+ hostkeys_update_ctx_free(ctx);
+}
+
/*
* Handle hostkeys@openssh.com global request to inform the client of all
* the server's hostkeys. The keys are checked against the user's
@@ -2097,34 +2307,35 @@
static int
client_input_hostkeys(void)
{
+ struct ssh *ssh = active_state; /* XXX */
const u_char *blob = NULL;
- u_int i, len = 0, nkeys = 0;
+ size_t i, len = 0;
struct sshbuf *buf = NULL;
- struct sshkey *key = NULL, **tmp, **keys = NULL;
- int r, success = 1;
- char *fp, *host_str = NULL, *ip_str = NULL;
+ struct sshkey *key = NULL, **tmp;
+ int r;
+ char *fp;
static int hostkeys_seen = 0; /* XXX use struct ssh */
extern struct sockaddr_storage hostaddr; /* XXX from ssh.c */
+ struct hostkeys_update_ctx *ctx;
- /*
- * NB. Return success for all cases other than protocol error. The
- * server doesn't need to know what the client does with its hosts
- * file.
- */
-
- blob = packet_get_string_ptr(&len);
- packet_check_eom();
+ ctx = xcalloc(1, sizeof(*ctx));
if (hostkeys_seen)
fatal("%s: server already sent hostkeys", __func__);
+ if (options.update_hostkeys == SSH_UPDATE_HOSTKEYS_ASK &&
+ options.batch_mode)
+ return 1; /* won't ask in batchmode, so don't even try */
if (!options.update_hostkeys || options.num_user_hostfiles <= 0)
return 1;
- if ((buf = sshbuf_from(blob, len)) == NULL)
- fatal("%s: sshbuf_from failed", __func__);
- while (sshbuf_len(buf) > 0) {
+ while (ssh_packet_remaining(ssh) > 0) {
sshkey_free(key);
key = NULL;
- if ((r = sshkey_froms(buf, &key)) != 0)
+ if ((r = sshpkt_get_string_direct(ssh, &blob, &len)) != 0) {
+ error("%s: couldn't parse message: %s",
+ __func__, ssh_err(r));
+ goto out;
+ }
+ if ((r = sshkey_from_blob(blob, len, &key)) != 0)
fatal("%s: parse key: %s", __func__, ssh_err(r));
fp = sshkey_fingerprint(key, options.fingerprint_hash,
SSH_FP_DEFAULT);
@@ -2140,47 +2351,107 @@
__func__, sshkey_ssh_name(key));
continue;
}
- if ((tmp = reallocarray(keys, nkeys + 1,
- sizeof(*keys))) == NULL)
- fatal("%s: reallocarray failed nkeys = %u",
- __func__, nkeys);
- keys = tmp;
- keys[nkeys++] = key;
+ /* Skip certs */
+ if (sshkey_is_cert(key)) {
+ debug3("%s: %s key is a certificate; skipping",
+ __func__, sshkey_ssh_name(key));
+ continue;
+ }
+ /* Ensure keys are unique */
+ for (i = 0; i < ctx->nkeys; i++) {
+ if (sshkey_equal(key, ctx->keys[i])) {
+ error("%s: received duplicated %s host key",
+ __func__, sshkey_ssh_name(key));
+ goto out;
+ }
+ }
+ /* Key is good, record it */
+ if ((tmp = reallocarray(ctx->keys, ctx->nkeys + 1,
+ sizeof(*ctx->keys))) == NULL)
+ fatal("%s: reallocarray failed nkeys = %zu",
+ __func__, ctx->nkeys);
+ ctx->keys = tmp;
+ ctx->keys[ctx->nkeys++] = key;
key = NULL;
}
- if (nkeys == 0) {
+ if (ctx->nkeys == 0) {
error("%s: server sent no hostkeys", __func__);
goto out;
}
+ if ((ctx->keys_seen = calloc(ctx->nkeys,
+ sizeof(*ctx->keys_seen))) == NULL)
+ fatal("%s: calloc failed", __func__);
get_hostfile_hostname_ipaddr(host,
options.check_host_ip ? (struct sockaddr *)&hostaddr : NULL,
- options.port, &host_str, options.check_host_ip ? &ip_str : NULL);
+ options.port, &ctx->host_str,
+ options.check_host_ip ? &ctx->ip_str : NULL);
- debug3("%s: update known hosts for %s%s%s with %u keys from server",
- __func__, host_str,
- options.check_host_ip ? " " : "",
- options.check_host_ip ? ip_str : "", nkeys);
-
- if ((r = hostfile_replace_entries(options.user_hostfiles[0],
- host_str, options.check_host_ip ? ip_str : NULL,
- keys, nkeys, options.hash_known_hosts, 0,
- options.fingerprint_hash)) != 0) {
- error("%s: hostfile_replace_entries failed: %s",
- __func__, ssh_err(r));
+ /* Find which keys we already know about. */
+ if ((r = hostkeys_foreach(options.user_hostfiles[0], hostkeys_find,
+ ctx, ctx->host_str, ctx->ip_str,
+ HKF_WANT_PARSE_KEY|HKF_WANT_MATCH)) != 0) {
+ error("%s: hostkeys_foreach failed: %s", __func__, ssh_err(r));
goto out;
}
+ /* Figure out if we have any new keys to add */
+ ctx->nnew = 0;
+ for (i = 0; i < ctx->nkeys; i++) {
+ if (!ctx->keys_seen[i])
+ ctx->nnew++;
+ }
+
+ debug3("%s: %zu keys from server: %zu new, %zu retained. %zu to remove",
+ __func__, ctx->nkeys, ctx->nnew, ctx->nkeys - ctx->nnew, ctx->nold);
+
+ if (ctx->nnew == 0 && ctx->nold != 0) {
+ /* We have some keys to remove. Just do it. */
+ update_known_hosts(ctx);
+ } else if (ctx->nnew != 0) {
+ /*
+ * We have received hitherto-unseen keys from the server.
+ * Ask the server to confirm ownership of the private halves.
+ */
+ debug3("%s: asking server to prove ownership for %zu keys",
+ __func__, ctx->nnew);
+ if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
+ (r = sshpkt_put_cstring(ssh,
+ "hostkeys-prove@openssh.com")) != 0 ||
+ (r = sshpkt_put_u8(ssh, 1)) != 0) /* bool: want reply */
+ fatal("%s: cannot prepare packet: %s",
+ __func__, ssh_err(r));
+ if ((buf = sshbuf_new()) == NULL)
+ fatal("%s: sshbuf_new", __func__);
+ for (i = 0; i < ctx->nkeys; i++) {
+ if (ctx->keys_seen[i])
+ continue;
+ sshbuf_reset(buf);
+ if ((r = sshkey_putb(ctx->keys[i], buf)) != 0)
+ fatal("%s: sshkey_putb: %s",
+ __func__, ssh_err(r));
+ if ((r = sshpkt_put_stringb(ssh, buf)) != 0)
+ fatal("%s: sshpkt_put_string: %s",
+ __func__, ssh_err(r));
+ }
+ if ((r = sshpkt_send(ssh)) != 0)
+ fatal("%s: sshpkt_send: %s", __func__, ssh_err(r));
+ client_register_global_confirm(
+ client_global_hostkeys_private_confirm, ctx);
+ ctx = NULL; /* will be freed in callback */
+ }
+
/* Success */
out:
- free(host_str);
- free(ip_str);
+ hostkeys_update_ctx_free(ctx);
sshkey_free(key);
- for (i = 0; i < nkeys; i++)
- sshkey_free(keys[i]);
sshbuf_free(buf);
- return success;
+ /*
+ * NB. Return success for all cases. The server doesn't need to know
+ * what the client does with its hosts file.
+ */
+ return 1;
}
static int