-/* $OpenBSD: ssh-agent.c,v 1.269 2021/01/26 00:47:47 djm Exp $ */
+/* $OpenBSD: ssh-agent.c,v 1.270 2021/01/26 00:53:31 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
/* Check confirmation of keysign request */
static int
-confirm_key(Identity *id)
+confirm_key(Identity *id, const char *extra)
{
char *p;
int ret = -1;
p = sshkey_fingerprint(id->key, fingerprint_hash, SSH_FP_DEFAULT);
if (p != NULL &&
- ask_permission("Allow use of key %s?\nKey fingerprint %s.",
- id->comment, p))
+ ask_permission("Allow use of key %s?\nKey fingerprint %s.%s%s",
+ id->comment, p,
+ extra == NULL ? "" : "\n", extra == NULL ? "" : extra))
ret = 0;
free(p);
}
/*
- * This function inspects a message to be signed by a FIDO key that has a
- * web-like application string (i.e. one that does not begin with "ssh:".
- * It checks that the message is one of those expected for SSH operations
- * (pubkey userauth, sshsig, CA key signing) to exclude signing challenges
- * for the web.
+ * Attempt to parse the contents of a buffer as a SSH publickey userauth
+ * request, checking its contents for consistency and matching the embedded
+ * key against the one that is being used for signing.
+ * Note: does not modify msg buffer.
+ * Optionally extract the username and session ID from the request.
*/
static int
-check_websafe_message_contents(struct sshkey *key,
- const u_char *msg, size_t len)
+parse_userauth_request(struct sshbuf *msg, const struct sshkey *expected_key,
+ char **userp, struct sshbuf **sess_idp)
{
- int matched = 0;
- struct sshbuf *b;
- u_char m, n;
- char *cp1 = NULL, *cp2 = NULL;
+ struct sshbuf *b = NULL, *sess_id = NULL;
+ char *user = NULL, *service = NULL, *method = NULL, *pkalg = NULL;
int r;
+ u_char t, sig_follows;
struct sshkey *mkey = NULL;
- if ((b = sshbuf_from(msg, len)) == NULL)
- fatal_f("sshbuf_new");
+ if (userp != NULL)
+ *userp = NULL;
+ if (sess_idp != NULL)
+ *sess_idp = NULL;
+ if ((b = sshbuf_fromb(msg)) == NULL)
+ fatal_f("sshbuf_fromb");
/* SSH userauth request */
- if ((r = sshbuf_get_string_direct(b, NULL, NULL)) == 0 && /* sess_id */
- (r = sshbuf_get_u8(b, &m)) == 0 && /* SSH2_MSG_USERAUTH_REQUEST */
- (r = sshbuf_get_cstring(b, NULL, NULL)) == 0 && /* server user */
- (r = sshbuf_get_cstring(b, &cp1, NULL)) == 0 && /* service */
- (r = sshbuf_get_cstring(b, &cp2, NULL)) == 0 && /* method */
- (r = sshbuf_get_u8(b, &n)) == 0 && /* sig-follows */
- (r = sshbuf_get_cstring(b, NULL, NULL)) == 0 && /* alg */
- (r = sshkey_froms(b, &mkey)) == 0 && /* key */
- sshbuf_len(b) == 0) {
- debug_f("parsed userauth");
- if (m == SSH2_MSG_USERAUTH_REQUEST && n == 1 &&
- strcmp(cp1, "ssh-connection") == 0 &&
- strcmp(cp2, "publickey") == 0 &&
- sshkey_equal(key, mkey)) {
- debug_f("well formed userauth");
- matched = 1;
- }
+ if ((r = sshbuf_froms(b, &sess_id)) != 0)
+ goto out;
+ if (sshbuf_len(sess_id) == 0) {
+ r = SSH_ERR_INVALID_FORMAT;
+ goto out;
}
- free(cp1);
- free(cp2);
- sshkey_free(mkey);
+ if ((r = sshbuf_get_u8(b, &t)) != 0 || /* SSH2_MSG_USERAUTH_REQUEST */
+ (r = sshbuf_get_cstring(b, &user, NULL)) != 0 || /* server user */
+ (r = sshbuf_get_cstring(b, &service, NULL)) != 0 || /* service */
+ (r = sshbuf_get_cstring(b, &method, NULL)) != 0 || /* method */
+ (r = sshbuf_get_u8(b, &sig_follows)) != 0 || /* sig-follows */
+ (r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 || /* alg */
+ (r = sshkey_froms(b, &mkey)) != 0) /* key */
+ goto out;
+ if (t != SSH2_MSG_USERAUTH_REQUEST ||
+ sig_follows != 1 ||
+ strcmp(service, "ssh-connection") != 0 ||
+ !sshkey_equal(expected_key, mkey) ||
+ sshkey_type_from_name(pkalg) != expected_key->type) {
+ r = SSH_ERR_INVALID_FORMAT;
+ goto out;
+ }
+ if (strcmp(method, "publickey") != 0) {
+ r = SSH_ERR_INVALID_FORMAT;
+ goto out;
+ }
+ if (sshbuf_len(b) != 0) {
+ r = SSH_ERR_INVALID_FORMAT;
+ goto out;
+ }
+ /* success */
+ r = 0;
+ debug3_f("well formed userauth");
+ if (userp != NULL) {
+ *userp = user;
+ user = NULL;
+ }
+ if (sess_idp != NULL) {
+ *sess_idp = sess_id;
+ sess_id = NULL;
+ }
+ out:
sshbuf_free(b);
- if (matched)
- return 1;
+ sshbuf_free(sess_id);
+ free(user);
+ free(service);
+ free(method);
+ free(pkalg);
+ sshkey_free(mkey);
+ return r;
+}
- if ((b = sshbuf_from(msg, len)) == NULL)
- fatal_f("sshbuf_new");
- cp1 = cp2 = NULL;
- mkey = NULL;
-
- /* SSHSIG */
- if ((r = sshbuf_cmp(b, 0, "SSHSIG", 6)) == 0 &&
- (r = sshbuf_consume(b, 6)) == 0 &&
- (r = sshbuf_get_cstring(b, NULL, NULL)) == 0 && /* namespace */
- (r = sshbuf_get_string_direct(b, NULL, NULL)) == 0 && /* reserved */
- (r = sshbuf_get_cstring(b, NULL, NULL)) == 0 && /* hashalg */
- (r = sshbuf_get_string_direct(b, NULL, NULL)) == 0 && /* H(msg) */
- sshbuf_len(b) == 0) {
- debug_f("parsed sshsig");
- matched = 1;
- }
+/*
+ * Attempt to parse the contents of a buffer as a SSHSIG signature request.
+ * Note: does not modify buffer.
+ */
+static int
+parse_sshsig_request(struct sshbuf *msg)
+{
+ int r;
+ struct sshbuf *b;
+ if ((b = sshbuf_fromb(msg)) == NULL)
+ fatal_f("sshbuf_fromb");
+
+ if ((r = sshbuf_cmp(b, 0, "SSHSIG", 6)) != 0 ||
+ (r = sshbuf_consume(b, 6)) != 0 ||
+ (r = sshbuf_get_cstring(b, NULL, NULL)) != 0 || /* namespace */
+ (r = sshbuf_get_string_direct(b, NULL, NULL)) != 0 || /* reserved */
+ (r = sshbuf_get_cstring(b, NULL, NULL)) != 0 || /* hashalg */
+ (r = sshbuf_get_string_direct(b, NULL, NULL)) != 0) /* H(msg) */
+ goto out;
+ if (sshbuf_len(b) != 0) {
+ r = SSH_ERR_INVALID_FORMAT;
+ goto out;
+ }
+ /* success */
+ r = 0;
+ out:
sshbuf_free(b);
- if (matched)
+ return r;
+}
+
+/*
+ * This function inspects a message to be signed by a FIDO key that has a
+ * web-like application string (i.e. one that does not begin with "ssh:".
+ * It checks that the message is one of those expected for SSH operations
+ * (pubkey userauth, sshsig, CA key signing) to exclude signing challenges
+ * for the web.
+ */
+static int
+check_websafe_message_contents(struct sshkey *key, struct sshbuf *data)
+{
+ if (parse_userauth_request(data, key, NULL, NULL) == 0) {
+ debug_f("signed data matches public key userauth request");
return 1;
+ }
+ if (parse_sshsig_request(data) == 0) {
+ debug_f("signed data matches SSHSIG signature request");
+ return 1;
+ }
- /* XXX CA signature operation */
+ /* XXX check CA signature operation */
error("web-origin key attempting to sign non-SSH message");
return 0;
static void
process_sign_request2(SocketEntry *e)
{
- const u_char *data;
u_char *signature = NULL;
- size_t dlen, slen = 0;
+ size_t i, slen = 0;
u_int compat = 0, flags;
int r, ok = -1;
char *fp = NULL;
- struct sshbuf *msg;
+ struct sshbuf *msg = NULL, *data = NULL;
struct sshkey *key = NULL;
struct identity *id;
struct notifier_ctx *notifier = NULL;
- if ((msg = sshbuf_new()) == NULL)
+ debug_f("entering");
+
+ if ((msg = sshbuf_new()) == NULL | (data = sshbuf_new()) == NULL)
fatal_f("sshbuf_new failed");
if ((r = sshkey_froms(e->request, &key)) != 0 ||
- (r = sshbuf_get_string_direct(e->request, &data, &dlen)) != 0 ||
+ (r = sshbuf_get_stringb(e->request, data)) != 0 ||
(r = sshbuf_get_u32(e->request, &flags)) != 0) {
error_fr(r, "parse");
goto send;
verbose_f("%s key not found", sshkey_type(key));
goto send;
}
- if (id->confirm && confirm_key(id) != 0) {
+ if (id->confirm && confirm_key(id, NULL) != 0) {
verbose_f("user refused key");
goto send;
}
if (sshkey_is_sk(id->key)) {
if (strncmp(id->key->sk_application, "ssh:", 4) != 0 &&
- !check_websafe_message_contents(key, data, dlen)) {
+ !check_websafe_message_contents(key, data)) {
/* error already logged */
goto send;
}
}
/* XXX support PIN required FIDO keys */
if ((r = sshkey_sign(id->key, &signature, &slen,
- data, dlen, agent_decode_alg(key, flags),
+ sshbuf_ptr(data), sshbuf_len(data), agent_decode_alg(key, flags),
id->sk_provider, NULL, compat)) != 0) {
error_fr(r, "sshkey_sign");
goto send;
ok = 0;
send:
notify_complete(notifier, "User presence confirmed");
- sshkey_free(key);
- free(fp);
+
if (ok == 0) {
if ((r = sshbuf_put_u8(msg, SSH2_AGENT_SIGN_RESPONSE)) != 0 ||
(r = sshbuf_put_string(msg, signature, slen)) != 0)
if ((r = sshbuf_put_stringb(e->output, msg)) != 0)
fatal_fr(r, "enqueue");
+ sshbuf_free(data);
sshbuf_free(msg);
+ sshkey_free(key);
+ free(fp);
free(signature);
}
projects / openbsd / commitdiff