Attachment 3561 Details for Bug 3375 – tweaked diff

[patch] tweaked diff

bz3375.diff (text/plain), 3.80 KB, created by Damien Miller on 2022-01-05 18:41:17 AEDT

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Creator: Damien Miller

Created: 2022-01-05 18:41:17 AEDT

Size: 3.80 KB

patch

obsolete

>commit 64db16b9c5e2618df9cafa44531771a9635627d0
>Author: Damien Miller <djm@mindrot.org>
>Date:   Wed Jan 5 18:24:11 2022 +1100
>
>    prefer rsa-sha2 for hostkey proofs
>
>diff --git a/kex.c b/kex.c
>index d3fe4ad..592c9af 100644
>--- a/kex.c
>+++ b/kex.c
>@@ -883,6 +883,18 @@ proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
> 	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)
> {
>@@ -918,6 +930,16 @@ kex_choose_conf(struct ssh *ssh)
> 		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) {
>diff --git a/kex.h b/kex.h
>index 638b02f..f1f583b 100644
>--- a/kex.h
>+++ b/kex.h
>@@ -102,6 +102,8 @@ enum kex_exchange {
> #define KEX_INIT_SENT			0x0001
> #define KEX_INITIAL			0x0002
> #define KEX_HAS_PUBKEY_HOSTBOUND	0x0004
>+#define KEX_RSA_SHA2_256_SUPPORTED 	0x0008 /* only set in server for now */
>+#define KEX_RSA_SHA2_512_SUPPORTED 	0x0010 /* only set in server for now */
> 
> struct sshenc {
> 	char	*name;
>diff --git a/serverloop.c b/serverloop.c
>index ab2af54..fdf5e59 100644
>--- a/serverloop.c
>+++ b/serverloop.c
>@@ -674,16 +674,17 @@ server_input_hostkeys_prove(struct ssh *ssh, struct sshbuf **respp)
> 	struct sshbuf *resp = NULL;
> 	struct sshbuf *sigbuf = NULL;
> 	struct sshkey *key = NULL, *key_pub = NULL, *key_prv = NULL;
>-	int r, ndx, kexsigtype, use_kexsigtype, success = 0;
>+	int r, ndx, success = 0;
> 	const u_char *blob;
>+	const char *sigalg, *kex_rsa_sigalg = NULL;
> 	u_char *sig = 0;
> 	size_t blen, slen;
> 
> 	if ((resp = sshbuf_new()) == NULL || (sigbuf = sshbuf_new()) == NULL)
> 		fatal_f("sshbuf_new");
>-
>-	kexsigtype = sshkey_type_plain(
>-	    sshkey_type_from_name(ssh->kex->hostkey_alg));
>+	if (sshkey_type_plain(sshkey_type_from_name(
>+	    ssh->kex->hostkey_alg)) == KEY_RSA)
>+		kex_rsa_sigalg = ssh->kex->hostkey_alg;
> 	while (ssh_packet_remaining(ssh) > 0) {
> 		sshkey_free(key);
> 		key = NULL;
>@@ -716,16 +717,24 @@ 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).
> 		 */
>-		use_kexsigtype = kexsigtype == KEY_RSA &&
>-		    sshkey_type_plain(key->type) == KEY_RSA;
>+		sigalg = NULL;
>+		if (sshkey_type_plain(key->type) == KEY_RSA) {
>+			if (kex_rsa_sigalg != NULL)
>+				sigalg = kex_rsa_sigalg;
>+			else if (ssh->kex->flags & KEX_RSA_SHA2_512_SUPPORTED)
>+				sigalg = "rsa-sha2-512";
>+			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,
> 		    "hostkeys-prove-00@openssh.com")) != 0 ||
> 		    (r = sshbuf_put_stringb(sigbuf,
> 		    ssh->kex->session_id)) != 0 ||
> 		    (r = sshkey_puts(key, sigbuf)) != 0 ||
> 		    (r = ssh->kex->sign(ssh, key_prv, key_pub, &sig, &slen,
>-		    sshbuf_ptr(sigbuf), sshbuf_len(sigbuf),
>-		    use_kexsigtype ? ssh->kex->hostkey_alg : NULL)) != 0 ||
>+		    sshbuf_ptr(sigbuf), sshbuf_len(sigbuf), sigalg)) != 0 ||
> 		    (r = sshbuf_put_string(resp, sig, slen)) != 0) {
> 			error_fr(r, "assemble signature");
> 			goto out;

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