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upstream: When using HostkeyAlgorithms to merely append or remove 

algorithms from the default set (i.e. HostkeyAlgorithms=+/-...), retain the
default behaviour of preferring those algorithms that have existing keys in
known_hosts; ok markus

OpenBSD-Commit-ID: 040e7fcc38ea00146b5d224ce31ce7a1795ee6ed
This commit is contained in:
djm@openbsd.org 2020-02-06 22:48:23 +00:00 committed by Damien Miller
parent c728848673
commit 96bd895a0a
1 changed files with 26 additions and 15 deletions
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41
sshconnect2.c
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@ -1,4 +1,4 @@
/* $OpenBSD: sshconnect2.c,v 1.319 2020/02/06 22:30:54 naddy Exp $ */ /* $OpenBSD: sshconnect2.c,v 1.320 2020/02/06 22:48:23 djm Exp $ */
/* /*
* Copyright (c) 2000 Markus Friedl. All rights reserved. * Copyright (c) 2000 Markus Friedl. All rights reserved.
* Copyright (c) 2008 Damien Miller. All rights reserved. * Copyright (c) 2008 Damien Miller. All rights reserved.
@ -119,7 +119,7 @@ order_hostkeyalgs(char *host, struct sockaddr *hostaddr, u_short port)
for (i = 0; i < options.num_system_hostfiles; i++) for (i = 0; i < options.num_system_hostfiles; i++)
load_hostkeys(hostkeys, hostname, options.system_hostfiles[i]); load_hostkeys(hostkeys, hostname, options.system_hostfiles[i]);
oavail = avail = xstrdup(kex_default_pk_alg()); oavail = avail = xstrdup(options.hostkeyalgorithms);
maxlen = strlen(avail) + 1; maxlen = strlen(avail) + 1;
first = xmalloc(maxlen); first = xmalloc(maxlen);
last = xmalloc(maxlen); last = xmalloc(maxlen);
@ -161,11 +161,28 @@ ssh_kex2(struct ssh *ssh, char *host, struct sockaddr *hostaddr, u_short port)
{ {
char *myproposal[PROPOSAL_MAX] = { KEX_CLIENT }; char *myproposal[PROPOSAL_MAX] = { KEX_CLIENT };
char *s, *all_key; char *s, *all_key;
int r; int r, use_known_hosts_order = 0;
xxx_host = host; xxx_host = host;
xxx_hostaddr = hostaddr; xxx_hostaddr = hostaddr;
/*
* If the user has not specified HostkeyAlgorithms, or has only
* appended or removed algorithms from that list then prefer algorithms
* that are in the list that are supported by known_hosts keys.
*/
if (options.hostkeyalgorithms == NULL ||
options.hostkeyalgorithms[0] == '-' ||
options.hostkeyalgorithms[0] == '+')
use_known_hosts_order = 1;
/* Expand or fill in HostkeyAlgorithms */
all_key = sshkey_alg_list(0, 0, 1, ',');
if (kex_assemble_names(&options.hostkeyalgorithms,
kex_default_pk_alg(), all_key) != 0)
fatal("%s: kex_assemble_namelist", __func__);
free(all_key);
if ((s = kex_names_cat(options.kex_algorithms, "ext-info-c")) == NULL) if ((s = kex_names_cat(options.kex_algorithms, "ext-info-c")) == NULL)
fatal("%s: kex_names_cat", __func__); fatal("%s: kex_names_cat", __func__);
myproposal[PROPOSAL_KEX_ALGS] = compat_kex_proposal(s); myproposal[PROPOSAL_KEX_ALGS] = compat_kex_proposal(s);
@ -178,21 +195,15 @@ ssh_kex2(struct ssh *ssh, char *host, struct sockaddr *hostaddr, u_short port)
(char *)compression_alg_list(options.compression); (char *)compression_alg_list(options.compression);
myproposal[PROPOSAL_MAC_ALGS_CTOS] = myproposal[PROPOSAL_MAC_ALGS_CTOS] =
myproposal[PROPOSAL_MAC_ALGS_STOC] = options.macs; myproposal[PROPOSAL_MAC_ALGS_STOC] = options.macs;
if (options.hostkeyalgorithms != NULL) { if (use_known_hosts_order) {
all_key = sshkey_alg_list(0, 0, 1, ','); /* Query known_hosts and prefer algorithms that appear there */
if (kex_assemble_names(&options.hostkeyalgorithms,
kex_default_pk_alg(), all_key) != 0)
fatal("%s: kex_assemble_namelist", __func__);
free(all_key);
myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] =
compat_pkalg_proposal(options.hostkeyalgorithms);
} else {
/* Enforce default */
options.hostkeyalgorithms = xstrdup(kex_default_pk_alg());
/* Prefer algorithms that we already have keys for */
myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] =
compat_pkalg_proposal( compat_pkalg_proposal(
order_hostkeyalgs(host, hostaddr, port)); order_hostkeyalgs(host, hostaddr, port));
} else {
/* Use specified HostkeyAlgorithms exactly */
myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] =
compat_pkalg_proposal(options.hostkeyalgorithms);
} }
if (options.rekey_limit || options.rekey_interval) if (options.rekey_limit || options.rekey_interval)