-/* $OpenBSD: ssh-agent.c,v 1.279 2021/11/18 03:31:44 djm Exp $ */
+/* $OpenBSD: ssh-agent.c,v 1.280 2021/12/19 22:09:23 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
#endif
/* Maximum accepted message length */
-#define AGENT_MAX_LEN (256*1024)
+#define AGENT_MAX_LEN (256*1024)
/* Maximum bytes to read from client socket */
-#define AGENT_RBUF_LEN (4096)
+#define AGENT_RBUF_LEN (4096)
+/* Maximum number of recorded session IDs/hostkeys per connection */
+#define AGENT_MAX_SESSION_IDS 16
+/* Maximum size of session ID */
+#define AGENT_MAX_SID_LEN 128
+
+/* XXX store hostkey_sid in a refcounted tree */
typedef enum {
AUTH_UNUSED = 0,
AUTH_CONNECTION = 2,
} sock_type;
+struct hostkey_sid {
+ struct sshkey *key;
+ struct sshbuf *sid;
+ int forwarded;
+};
+
typedef struct socket_entry {
int fd;
sock_type type;
struct sshbuf *input;
struct sshbuf *output;
struct sshbuf *request;
+ size_t nsession_ids;
+ struct hostkey_sid *session_ids;
} SocketEntry;
u_int sockets_alloc = 0;
static void
close_socket(SocketEntry *e)
{
+ size_t i;
+
close(e->fd);
sshbuf_free(e->input);
sshbuf_free(e->output);
sshbuf_free(e->request);
+ for (i = 0; i < e->nsession_ids; i++) {
+ sshkey_free(e->session_ids[i].key);
+ sshbuf_free(e->session_ids[i].sid);
+ }
+ free(e->session_ids);
memset(e, '\0', sizeof(*e));
e->fd = -1;
e->type = AUTH_UNUSED;
return 0;
}
+static int
+buf_equal(const struct sshbuf *a, const struct sshbuf *b)
+{
+ if (sshbuf_ptr(a) == NULL || sshbuf_ptr(b) == NULL)
+ return SSH_ERR_INVALID_ARGUMENT;
+ if (sshbuf_len(a) != sshbuf_len(b))
+ return SSH_ERR_INVALID_FORMAT;
+ if (timingsafe_bcmp(sshbuf_ptr(a), sshbuf_ptr(b), sshbuf_len(a)) != 0)
+ return SSH_ERR_INVALID_FORMAT;
+ return 0;
+}
+
/* ssh2 only */
static void
process_sign_request2(SocketEntry *e)
{
u_char *signature = NULL;
- size_t slen = 0;
+ size_t i, slen = 0;
u_int compat = 0, flags;
int r, ok = -1;
- char *fp = NULL;
- struct sshbuf *msg = NULL, *data = NULL;
+ char *fp = NULL, *user = NULL, *sig_dest = NULL;
+ struct sshbuf *msg = NULL, *data = NULL, *sid = NULL;
struct sshkey *key = NULL;
struct identity *id;
struct notifier_ctx *notifier = NULL;
verbose_f("%s key not found", sshkey_type(key));
goto send;
}
- if (id->confirm && confirm_key(id, NULL) != 0) {
+ /*
+ * If session IDs were recorded for this socket, then use them to
+ * annotate the confirmation messages with the host keys.
+ */
+ if (e->nsession_ids > 0 &&
+ parse_userauth_request(data, key, &user, &sid) == 0) {
+ /*
+ * session ID from userauth request should match the final
+ * ID in the list recorded in the socket, unless the ssh
+ * client at that point lacks the binding extension (or if
+ * an attacker is trying to steal use of the agent).
+ */
+ i = e->nsession_ids - 1;
+ if (buf_equal(sid, e->session_ids[i].sid) == 0) {
+ if ((fp = sshkey_fingerprint(e->session_ids[i].key,
+ SSH_FP_HASH_DEFAULT, SSH_FP_DEFAULT)) == NULL)
+ fatal_f("fingerprint failed");
+ debug3_f("destination %s %s (slot %zu)",
+ sshkey_type(e->session_ids[i].key), fp, i);
+ xasprintf(&sig_dest, "public key request for "
+ "target user \"%s\" to %s %s", user,
+ sshkey_type(e->session_ids[i].key), fp);
+ free(fp);
+ fp = NULL;
+ }
+ }
+ if (id->confirm && confirm_key(id, sig_dest) != 0) {
verbose_f("user refused key");
goto send;
}
SSH_FP_DEFAULT)) == NULL)
fatal_f("fingerprint failed");
notifier = notify_start(0,
- "Confirm user presence for key %s %s",
- sshkey_type(id->key), fp);
+ "Confirm user presence for key %s %s%s%s",
+ sshkey_type(id->key), fp,
+ sig_dest == NULL ? "" : "\n",
+ sig_dest == NULL ? "" : sig_dest);
}
}
/* XXX support PIN required FIDO keys */
if ((r = sshbuf_put_stringb(e->output, msg)) != 0)
fatal_fr(r, "enqueue");
+ sshbuf_free(sid);
sshbuf_free(data);
sshbuf_free(msg);
sshkey_free(key);
free(fp);
free(signature);
+ free(sig_dest);
+ free(user);
}
/* shared */
}
#endif /* ENABLE_PKCS11 */
+static int
+process_ext_session_bind(SocketEntry *e)
+{
+ int r, sid_match, key_match;
+ struct sshkey *key = NULL;
+ struct sshbuf *sid = NULL, *sig = NULL;
+ char *fp = NULL;
+ u_char fwd;
+ size_t i;
+
+ debug2_f("entering");
+ if ((r = sshkey_froms(e->request, &key)) != 0 ||
+ (r = sshbuf_froms(e->request, &sid)) != 0 ||
+ (r = sshbuf_froms(e->request, &sig)) != 0 ||
+ (r = sshbuf_get_u8(e->request, &fwd)) != 0) {
+ error_fr(r, "parse");
+ goto out;
+ }
+ if ((fp = sshkey_fingerprint(key, SSH_FP_HASH_DEFAULT,
+ SSH_FP_DEFAULT)) == NULL)
+ fatal_f("fingerprint failed");
+ /* check signature with hostkey on session ID */
+ if ((r = sshkey_verify(key, sshbuf_ptr(sig), sshbuf_len(sig),
+ sshbuf_ptr(sid), sshbuf_len(sid), NULL, 0, NULL)) != 0) {
+ error_fr(r, "sshkey_verify for %s %s", sshkey_type(key), fp);
+ goto out;
+ }
+ /* check whether sid/key already recorded */
+ for (i = 0; i < e->nsession_ids; i++) {
+ sid_match = buf_equal(sid, e->session_ids[i].sid) == 0;
+ key_match = sshkey_equal(key, e->session_ids[i].key);
+ if (sid_match && key_match) {
+ debug_f("session ID already recorded for %s %s",
+ sshkey_type(key), fp);
+ r = 0;
+ goto out;
+ } else if (sid_match) {
+ error_f("session ID recorded against different key "
+ "for %s %s", sshkey_type(key), fp);
+ r = -1;
+ goto out;
+ }
+ /*
+ * new sid with previously-seen key can happen, e.g. multiple
+ * connections to the same host.
+ */
+ }
+ /* record new key/sid */
+ if (e->nsession_ids >= AGENT_MAX_SESSION_IDS) {
+ error_f("too many session IDs recorded");
+ goto out;
+ }
+ e->session_ids = xrecallocarray(e->session_ids, e->nsession_ids,
+ e->nsession_ids + 1, sizeof(*e->session_ids));
+ i = e->nsession_ids++;
+ debug_f("recorded %s %s (slot %zu of %d)", sshkey_type(key), fp, i,
+ AGENT_MAX_SESSION_IDS);
+ e->session_ids[i].key = key;
+ e->session_ids[i].forwarded = fwd != 0;
+ key = NULL; /* transferred */
+ /* can't transfer sid; it's refcounted and scoped to request's life */
+ if ((e->session_ids[i].sid = sshbuf_new()) == NULL)
+ fatal_f("sshbuf_new");
+ if ((r = sshbuf_putb(e->session_ids[i].sid, sid)) != 0)
+ fatal_fr(r, "sshbuf_putb session ID");
+ /* success */
+ r = 0;
+ out:
+ sshkey_free(key);
+ sshbuf_free(sid);
+ sshbuf_free(sig);
+ return r == 0 ? 1 : 0;
+}
+
+static void
+process_extension(SocketEntry *e)
+{
+ int r, success = 0;
+ char *name;
+
+ debug2_f("entering");
+ if ((r = sshbuf_get_cstring(e->request, &name, NULL)) != 0) {
+ error_fr(r, "parse");
+ goto send;
+ }
+ if (strcmp(name, "session-bind@openssh.com") == 0)
+ success = process_ext_session_bind(e);
+ else
+ debug_f("unsupported extension \"%s\"", name);
+send:
+ send_status(e, success);
+}
/*
* dispatch incoming message.
* returns 1 on success, 0 for incomplete messages or -1 on error.
process_remove_smartcard_key(e);
break;
#endif /* ENABLE_PKCS11 */
+ case SSH_AGENTC_EXTENSION:
+ process_extension(e);
+ break;
default:
/* Unknown message. Respond with failure. */
error("Unknown message %d", type);
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