[openssh-commits] [openssh] 02/04: upstream: Tweak ordering of certificates tried during pubkey
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commit 6fe6ab77daa4472d0243580e355e0674a95b8acb
Author: djm at openbsd.org <djm at openbsd.org>
AuthorDate: Mon Aug 3 06:50:49 2026 +0000
upstream: Tweak ordering of certificates tried during pubkey
authentication to prefer FIDO keys that do not require user presence (touch)
first, followed by ones that do and with FIDO keys that require user
verification via PIN or biometrics last.
This effectively tries low-friction authenticators before higher
friction authenticators.
ok dtucker@
OpenBSD-Commit-ID: 067076c652dbb4f2aa89c6e82b19d8cbfec1d1be
---
sshconnect2.c | 115 ++++++++++++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 107 insertions(+), 8 deletions(-)
diff --git a/sshconnect2.c b/sshconnect2.c
index b2eb17bd4..a28137c76 100644
--- a/sshconnect2.c
+++ b/sshconnect2.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshconnect2.c,v 1.391 2026/08/03 06:47:24 djm Exp $ */
+/* $OpenBSD: sshconnect2.c,v 1.392 2026/08/03 06:50:49 djm Exp $ */
/*
* Copyright (c) 2000 Markus Friedl. All rights reserved.
* Copyright (c) 2008 Damien Miller. All rights reserved.
@@ -1668,19 +1668,109 @@ get_agent_identities(struct ssh *ssh, int *agent_fdp,
return 0;
}
+/*
+ * Returns nonzero if the certificate extensions/critical-options section
+ * has the specified option present, zero otherwise.
+ */
+static int
+cert_has_option(struct sshbuf *oblob, const char *target)
+{
+ struct sshbuf *c = NULL, *data = NULL;
+ char *name = NULL;
+ int r, found = 0;
+
+ if (oblob == NULL || (c = sshbuf_fromb(oblob)) == NULL)
+ return 0;
+ while (sshbuf_len(c) > 0) {
+ sshbuf_free(data);
+ data = NULL;
+ free(name);
+ name = NULL;
+ if ((r = sshbuf_get_cstring(c, &name, NULL)) != 0 ||
+ (r = sshbuf_froms(c, &data)) != 0)
+ break;
+ if (strcmp(name, target) == 0) {
+ found = 1;
+ break;
+ }
+ }
+ sshbuf_free(data);
+ free(name);
+ sshbuf_free(c);
+ return found;
+}
+
+/*
+ * Returns an integer describing the priority of the identity
+ * within its group. Lower numbers are higher priority.
+ */
+#define MAX_ID_PRIORITY 3
+static int
+identity_prioritise(struct identity *id)
+{
+ if (id == NULL || id->key == NULL)
+ return 3;
+ if (!sshkey_is_cert(id->key) || id->key->cert == NULL)
+ return 3;
+ if (sshkey_is_sk(id->key) &&
+ cert_has_option(id->key->cert->critical, "verify-required"))
+ return 2;
+ if (sshkey_is_sk(id->key) &&
+ cert_has_option(id->key->cert->extensions, "no-touch-required"))
+ return 0;
+ return 1;
+}
+
+static void
+order_identities_by_prio(struct idlist *list)
+{
+ struct idlist prio[MAX_ID_PRIORITY + 1], sorted;
+ struct identity *id, *tmp, *dummy;
+ int p;
+
+ for (p = 0; p <= MAX_ID_PRIORITY; p++)
+ TAILQ_INIT(&prio[p]);
+ TAILQ_INIT(&sorted);
+
+ TAILQ_FOREACH_SAFE(id, list, next, tmp) {
+ if (id->userprovided)
+ continue;
+ dummy = xcalloc(1, sizeof(*dummy));
+ dummy->userprovided = -1;
+ TAILQ_INSERT_BEFORE(id, dummy, next);
+ TAILQ_REMOVE(list, id, next);
+ p = identity_prioritise(id);
+ if (p < 0 || p > MAX_ID_PRIORITY)
+ fatal_f("internal error: bad priority");
+ TAILQ_INSERT_TAIL(&prio[p], id, next);
+ }
+ for (p = 0; p <= MAX_ID_PRIORITY; p++)
+ TAILQ_CONCAT(&sorted, &prio[p], next);
+
+ TAILQ_FOREACH_SAFE(id, list, next, tmp) {
+ if (id->userprovided != -1)
+ continue;
+ struct identity *s = TAILQ_FIRST(&sorted);
+ TAILQ_REMOVE(&sorted, s, next);
+ TAILQ_INSERT_BEFORE(id, s, next);
+ TAILQ_REMOVE(list, id, next);
+ free(id);
+ }
+}
+
/*
* try keys in the following order:
* 1. certificates listed in the config file
- * 2. other input certificates
- * 3. agent keys that are found in the config file
- * 4. other agent keys
+ * 2. agent keys that are found in the config file
+ * 3. other agent keys
+ * 4. PKCS#11 keys that are found in the config file
* 5. keys that are only listed in the config file
*/
static void
pubkey_prepare(struct ssh *ssh, Authctxt *authctxt)
{
struct identity *id, *id2, *tmp;
- struct idlist agent, files, *preferred;
+ struct idlist agent, files, certs, agent_keys, *preferred;
struct sshkey *key;
int disallowed, agent_fd = -1, i, r, found;
size_t j;
@@ -1689,6 +1779,8 @@ pubkey_prepare(struct ssh *ssh, Authctxt *authctxt)
TAILQ_INIT(&agent); /* keys from the agent */
TAILQ_INIT(&files); /* keys from the config file */
+ TAILQ_INIT(&certs); /* certificates specified by user */
+ TAILQ_INIT(&agent_keys); /* keys supported by the agent */
preferred = &authctxt->keys;
TAILQ_INIT(preferred); /* preferred order of keys */
@@ -1715,6 +1807,7 @@ pubkey_prepare(struct ssh *ssh, Authctxt *authctxt)
id->userprovided = options.identity_file_userprovided[i];
TAILQ_INSERT_TAIL(&files, id, next);
}
+
/* list of certificates specified by user */
for (i = 0; i < options.num_certificate_files; i++) {
key = options.certificates[i];
@@ -1736,8 +1829,11 @@ pubkey_prepare(struct ssh *ssh, Authctxt *authctxt)
id->key = key;
id->filename = xstrdup(options.certificate_files[i]);
id->userprovided = options.certificate_file_userprovided[i];
- TAILQ_INSERT_TAIL(preferred, id, next);
+ TAILQ_INSERT_TAIL(&certs, id, next);
}
+ order_identities_by_prio(&certs);
+ TAILQ_CONCAT(preferred, &certs, next);
+
/* list of keys supported by the agent */
if ((r = get_agent_identities(ssh, &agent_fd, &idlist)) == 0) {
for (j = 0; j < idlist->nkeys; j++) {
@@ -1755,7 +1851,7 @@ pubkey_prepare(struct ssh *ssh, Authctxt *authctxt)
*/
if (sshkey_equal(idlist->keys[j], id->key)) {
TAILQ_REMOVE(&files, id, next);
- TAILQ_INSERT_TAIL(preferred, id, next);
+ TAILQ_INSERT_TAIL(&agent_keys, id, next);
id->agent_fd = agent_fd;
found = 1;
break;
@@ -1773,8 +1869,10 @@ pubkey_prepare(struct ssh *ssh, Authctxt *authctxt)
}
}
ssh_free_identitylist(idlist);
+ TAILQ_CONCAT(&agent_keys, &agent, next);
+ order_identities_by_prio(&agent_keys);
/* append remaining agent keys */
- TAILQ_CONCAT(preferred, &agent, next);
+ TAILQ_CONCAT(preferred, &agent_keys, next);
authctxt->agent_fd = agent_fd;
}
/* Prefer PKCS11 keys that are explicitly listed */
@@ -1799,6 +1897,7 @@ pubkey_prepare(struct ssh *ssh, Authctxt *authctxt)
freezero(id, sizeof(*id));
}
}
+ order_identities_by_prio(&files);
/* append remaining keys from the config file */
TAILQ_CONCAT(preferred, &files, next);
/* finally, filter by PubkeyAcceptedAlgorithms */
--
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