From: djm@openbsd.org <djm@openbsd.org>
Date: Tue, 26 Nov 2024 22:01:37 +0000 (+0000)
Subject: upstream: Explicitly specify the signature algorithm when signing
X-Git-Tag: V_10_0_P1~139
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=84023656d91b78f1ef86c8321ec563f2e90f7227;p=thirdparty%2Fopenssh-portable.git

upstream: Explicitly specify the signature algorithm when signing

hostkeys-prove requests.

Fixes a corner-case triggered by UpdateHostKeys with one or more unknown
host keys stored in ssh-agent where sshd refuses to accept the signature
coming back from the agent.

Report/fix from Maxime Rey

OpenBSD-Commit-ID: 460c7d527a24f92b7e5f68ca1a2fa242ebf0d086
---

diff --git a/serverloop.c b/serverloop.c
index 757cc6f02..40ddfb042 100644
--- a/serverloop.c
+++ b/serverloop.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: serverloop.c,v 1.240 2024/06/17 08:28:31 djm Exp $ */
+/* $OpenBSD: serverloop.c,v 1.241 2024/11/26 22:01:37 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -690,7 +690,7 @@ server_input_hostkeys_prove(struct ssh *ssh, struct sshbuf **respp)
 		 * For RSA keys, prefer to use the signature type negotiated
 		 * during KEX to the default (SHA1).
 		 */
-		sigalg = NULL;
+		sigalg = sshkey_ssh_name(key);
 		if (sshkey_type_plain(key->type) == KEY_RSA) {
 			if (kex_rsa_sigalg != NULL)
 				sigalg = kex_rsa_sigalg;
@@ -699,6 +699,7 @@ server_input_hostkeys_prove(struct ssh *ssh, struct sshbuf **respp)
 			else if (ssh->kex->flags & KEX_RSA_SHA2_256_SUPPORTED)
 				sigalg = "rsa-sha2-256";
 		}
+
 		debug3_f("sign %s key (index %d) using sigalg %s",
 		    sshkey_type(key), ndx, sigalg == NULL ? "default" : sigalg);
 		if ((r = sshbuf_put_cstring(sigbuf,