upstream: make UpdateHostkeys still more conservative: refuse to

proceed if one of the keys offered by the server is already in known_hosts
under another name. This avoid collisions between address entries for
different host aliases when CheckHostIP=yes

Also, do not attempt to fix known_hosts with incomplete host/ip matches
when there are no new or deprecated hostkeys.

OpenBSD-Commit-ID: 95c19842f7c41f9bd9c92aa6441a278c0fd0c4a3

diff --git a/clientloop.c b/clientloop.c
index 2d401923371175cfcb93dba1ad72b6f45d671e4e..8cd6f710659c6cd764545ae0fcb13a0ac32d5d9d 100644 (file)
--- a/clientloop.c
+++ b/clientloop.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: clientloop.c,v 1.352 2020/10/11 22:14:38 djm Exp $ */
+/* $OpenBSD: clientloop.c,v 1.353 2020/10/14 00:55:17 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1834,6 +1834,7 @@ struct hostkeys_update_ctx {
        int complex_hostspec;   /* wildcard or manual pattern-list host name */
        int ca_available;       /* saw CA key for this host */
        int old_key_seen;       /* saw old key with other name/addr */
+       int other_name_seen;    /* saw key with other name/addr */
 };
 
 static void
@@ -1887,9 +1888,39 @@ hostkeys_find(struct hostkey_foreach_line *l, void *_ctx)
        size_t i;
        struct sshkey **tmp;
 
-       if (l->status != HKF_STATUS_MATCHED || l->key == NULL ||
-           l->marker != MRK_NONE)
+       if (l->key == NULL)
                return 0;
+       if (l->status != HKF_STATUS_MATCHED) {
+               /* Record if one of the keys appears on a non-matching line */
+               for (i = 0; i < ctx->nkeys; i++) {
+                       if (sshkey_equal(l->key, ctx->keys[i])) {
+                               ctx->other_name_seen = 1;
+                               debug3("%s: found %s key under different "
+                                   "name/addr at %s:%ld", __func__,
+                                   sshkey_ssh_name(ctx->keys[i]),
+                                   l->path, l->linenum);
+                               return 0;
+                       }
+               }
+               return 0;
+       }
+       /* Don't proceed if revocation or CA markers are present */
+       /* XXX relax this */
+       if (l->marker != MRK_NONE) {
+               debug3("%s: hostkeys file %s:%ld has CA/revocation marker",
+                   __func__, l->path, l->linenum);
+               ctx->complex_hostspec = 1;
+               return 0;
+       }
+
+       /* Record if address matched against a different hostname. */
+       if (ctx->ip_str != NULL && (l->match & HKF_MATCH_HOST) == 0 &&
+           strchr(l->hosts, ',') != NULL) {
+               ctx->other_name_seen = 1;
+               debug3("%s: found address %s against different hostname at "
+                   "%s:%ld", __func__, ctx->ip_str, l->path, l->linenum);
+               return 0;
+       }
 
        /*
         * UpdateHostkeys is skipped for wildcard host names and hostnames
@@ -2307,19 +2338,28 @@ client_input_hostkeys(struct ssh *ssh)
                        ctx->nincomplete++;
        }
 
-
        debug3("%s: %zu server keys: %zu new, %zu retained, "
            "%zu incomplete match. %zu to remove", __func__, ctx->nkeys,
            ctx->nnew, ctx->nkeys - ctx->nnew - ctx->nincomplete,
            ctx->nincomplete, ctx->nold);
 
-       if (ctx->complex_hostspec &&
-           (ctx->nnew != 0 || ctx->nold != 0 || ctx->nincomplete != 0)) {
-               debug("%s: manual list or wildcard host pattern found, "
-                   "skipping UserKnownHostsFile update", __func__);
+       if (ctx->nnew == 0 && ctx->nold == 0) {
+               debug("%s: no new or deprecated keys from server", __func__);
                goto out;
        }
 
+       /* Various reasons why we cannot proceed with the update */
+       if (ctx->complex_hostspec) {
+               debug("%s: CA/revocation marker, manual host list or wildcard "
+                   "host pattern found, skipping UserKnownHostsFile update",
+                   __func__);
+               goto out;
+       }
+       if (ctx->other_name_seen) {
+               debug("%s: host key found matching a different name/address, "
+                   "skipping UserKnownHostsFile update", __func__);
+               goto out;
+       }
        /*
         * If removing keys, check whether they appear under different
         * names/addresses and refuse to proceed if they do. This avoids
@@ -2339,45 +2379,43 @@ client_input_hostkeys(struct ssh *ssh)
                }
        }
 
-       if (ctx->nnew == 0 && (ctx->nold != 0 || ctx->nincomplete != 0)) {
+       if (ctx->nnew == 0) {
                /*
                 * We have some keys to remove or fix matching for.
                 * We can proceed to do this without requiring a fresh proof
                 * from the server.
                 */
                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-00@openssh.com")) != 0 ||
-                   (r = sshpkt_put_u8(ssh, 1)) != 0) /* bool: want reply */
-                       fatal("%s: cannot prepare packet: %s",
+               goto out;
+       }
+       /*
+        * We have received previously-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-00@openssh.com")) != 0 ||
+           (r = sshpkt_put_u8(ssh, 1)) != 0) /* bool: want reply */
+               fatal("%s: prepare hostkeys-prove: %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_match[i])
+                       continue;
+               sshbuf_reset(buf);
+               if ((r = sshkey_putb(ctx->keys[i], buf)) != 0 ||
+                   (r = sshpkt_put_stringb(ssh, buf)) != 0) {
+                       fatal("%s: assemble hostkeys-prove: %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_match[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 */
        }
+       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: