upstream: more ssh-agent refactoring
Allow confirm_key() to accept an additional reason suffix Factor publickey userauth parsing out into its own function and allow it to optionally return things it parsed out of the message to its caller. feedback/ok markus@ OpenBSD-Commit-ID: 29006515617d1aa2d8b85cd2bf667e849146477e
This commit is contained in:
djm@openbsd.org
Damien Miller
parent
dfe18a2955
commit
e0e8bee802
205
ssh-agent.c
205
ssh-agent.c
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@ -1,4 +1,4 @@
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/* $OpenBSD: ssh-agent.c,v 1.269 2021/01/26 00:47:47 djm Exp $ */
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/* $OpenBSD: ssh-agent.c,v 1.270 2021/01/26 00:53:31 djm Exp $ */
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/*
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* Author: Tatu Ylonen <ylo@cs.hut.fi>
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* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
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@ -216,15 +216,16 @@ lookup_identity(struct sshkey *key)
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/* Check confirmation of keysign request */
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static int
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confirm_key(Identity *id)
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confirm_key(Identity *id, const char *extra)
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{
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char *p;
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int ret = -1;
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p = sshkey_fingerprint(id->key, fingerprint_hash, SSH_FP_DEFAULT);
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if (p != NULL &&
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ask_permission("Allow use of key %s?\nKey fingerprint %s.",
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id->comment, p))
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ask_permission("Allow use of key %s?\nKey fingerprint %s.%s%s",
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id->comment, p,
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extra == NULL ? "" : "\n", extra == NULL ? "" : extra))
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ret = 0;
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free(p);
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@ -288,6 +289,114 @@ agent_decode_alg(struct sshkey *key, u_int flags)
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return NULL;
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}
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/*
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* Attempt to parse the contents of a buffer as a SSH publickey userauth
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* request, checking its contents for consistency and matching the embedded
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* key against the one that is being used for signing.
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* Note: does not modify msg buffer.
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* Optionally extract the username and session ID from the request.
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*/
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static int
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parse_userauth_request(struct sshbuf *msg, const struct sshkey *expected_key,
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char **userp, struct sshbuf **sess_idp)
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{
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struct sshbuf *b = NULL, *sess_id = NULL;
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char *user = NULL, *service = NULL, *method = NULL, *pkalg = NULL;
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int r;
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u_char t, sig_follows;
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struct sshkey *mkey = NULL;
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if (userp != NULL)
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*userp = NULL;
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if (sess_idp != NULL)
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*sess_idp = NULL;
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if ((b = sshbuf_fromb(msg)) == NULL)
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fatal_f("sshbuf_fromb");
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/* SSH userauth request */
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if ((r = sshbuf_froms(b, &sess_id)) != 0)
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goto out;
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if (sshbuf_len(sess_id) == 0) {
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r = SSH_ERR_INVALID_FORMAT;
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goto out;
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}
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if ((r = sshbuf_get_u8(b, &t)) != 0 || /* SSH2_MSG_USERAUTH_REQUEST */
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(r = sshbuf_get_cstring(b, &user, NULL)) != 0 || /* server user */
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(r = sshbuf_get_cstring(b, &service, NULL)) != 0 || /* service */
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(r = sshbuf_get_cstring(b, &method, NULL)) != 0 || /* method */
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(r = sshbuf_get_u8(b, &sig_follows)) != 0 || /* sig-follows */
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(r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 || /* alg */
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(r = sshkey_froms(b, &mkey)) != 0) /* key */
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goto out;
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if (t != SSH2_MSG_USERAUTH_REQUEST ||
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sig_follows != 1 ||
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strcmp(service, "ssh-connection") != 0 ||
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!sshkey_equal(expected_key, mkey) ||
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sshkey_type_from_name(pkalg) != expected_key->type) {
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r = SSH_ERR_INVALID_FORMAT;
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goto out;
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}
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if (strcmp(method, "publickey") != 0) {
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r = SSH_ERR_INVALID_FORMAT;
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goto out;
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}
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if (sshbuf_len(b) != 0) {
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r = SSH_ERR_INVALID_FORMAT;
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goto out;
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}
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/* success */
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r = 0;
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debug3_f("well formed userauth");
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if (userp != NULL) {
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*userp = user;
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user = NULL;
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}
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if (sess_idp != NULL) {
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*sess_idp = sess_id;
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sess_id = NULL;
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}
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out:
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sshbuf_free(b);
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sshbuf_free(sess_id);
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free(user);
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free(service);
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free(method);
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free(pkalg);
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sshkey_free(mkey);
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return r;
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}
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/*
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* Attempt to parse the contents of a buffer as a SSHSIG signature request.
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* Note: does not modify buffer.
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*/
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static int
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parse_sshsig_request(struct sshbuf *msg)
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{
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int r;
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struct sshbuf *b;
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if ((b = sshbuf_fromb(msg)) == NULL)
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fatal_f("sshbuf_fromb");
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if ((r = sshbuf_cmp(b, 0, "SSHSIG", 6)) != 0 ||
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(r = sshbuf_consume(b, 6)) != 0 ||
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(r = sshbuf_get_cstring(b, NULL, NULL)) != 0 || /* namespace */
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(r = sshbuf_get_string_direct(b, NULL, NULL)) != 0 || /* reserved */
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(r = sshbuf_get_cstring(b, NULL, NULL)) != 0 || /* hashalg */
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(r = sshbuf_get_string_direct(b, NULL, NULL)) != 0) /* H(msg) */
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goto out;
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if (sshbuf_len(b) != 0) {
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r = SSH_ERR_INVALID_FORMAT;
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goto out;
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}
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/* success */
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r = 0;
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out:
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sshbuf_free(b);
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return r;
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}
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/*
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* This function inspects a message to be signed by a FIDO key that has a
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* web-like application string (i.e. one that does not begin with "ssh:".
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@ -296,67 +405,18 @@ agent_decode_alg(struct sshkey *key, u_int flags)
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* for the web.
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*/
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static int
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check_websafe_message_contents(struct sshkey *key,
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const u_char *msg, size_t len)
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check_websafe_message_contents(struct sshkey *key, struct sshbuf *data)
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{
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int matched = 0;
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struct sshbuf *b;
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u_char m, n;
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char *cp1 = NULL, *cp2 = NULL;
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int r;
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struct sshkey *mkey = NULL;
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if ((b = sshbuf_from(msg, len)) == NULL)
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fatal_f("sshbuf_new");
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/* SSH userauth request */
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if ((r = sshbuf_get_string_direct(b, NULL, NULL)) == 0 && /* sess_id */
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(r = sshbuf_get_u8(b, &m)) == 0 && /* SSH2_MSG_USERAUTH_REQUEST */
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(r = sshbuf_get_cstring(b, NULL, NULL)) == 0 && /* server user */
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(r = sshbuf_get_cstring(b, &cp1, NULL)) == 0 && /* service */
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(r = sshbuf_get_cstring(b, &cp2, NULL)) == 0 && /* method */
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(r = sshbuf_get_u8(b, &n)) == 0 && /* sig-follows */
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(r = sshbuf_get_cstring(b, NULL, NULL)) == 0 && /* alg */
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(r = sshkey_froms(b, &mkey)) == 0 && /* key */
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sshbuf_len(b) == 0) {
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debug_f("parsed userauth");
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if (m == SSH2_MSG_USERAUTH_REQUEST && n == 1 &&
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strcmp(cp1, "ssh-connection") == 0 &&
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strcmp(cp2, "publickey") == 0 &&
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sshkey_equal(key, mkey)) {
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debug_f("well formed userauth");
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matched = 1;
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}
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}
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free(cp1);
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free(cp2);
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sshkey_free(mkey);
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sshbuf_free(b);
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if (matched)
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if (parse_userauth_request(data, key, NULL, NULL) == 0) {
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debug_f("signed data matches public key userauth request");
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return 1;
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}
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if (parse_sshsig_request(data) == 0) {
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debug_f("signed data matches SSHSIG signature request");
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return 1;
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if ((b = sshbuf_from(msg, len)) == NULL)
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fatal_f("sshbuf_new");
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cp1 = cp2 = NULL;
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mkey = NULL;
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/* SSHSIG */
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if ((r = sshbuf_cmp(b, 0, "SSHSIG", 6)) == 0 &&
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(r = sshbuf_consume(b, 6)) == 0 &&
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(r = sshbuf_get_cstring(b, NULL, NULL)) == 0 && /* namespace */
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(r = sshbuf_get_string_direct(b, NULL, NULL)) == 0 && /* reserved */
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(r = sshbuf_get_cstring(b, NULL, NULL)) == 0 && /* hashalg */
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(r = sshbuf_get_string_direct(b, NULL, NULL)) == 0 && /* H(msg) */
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sshbuf_len(b) == 0) {
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debug_f("parsed sshsig");
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matched = 1;
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}
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sshbuf_free(b);
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if (matched)
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return 1;
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/* XXX CA signature operation */
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/* XXX check CA signature operation */
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error("web-origin key attempting to sign non-SSH message");
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return 0;
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@ -366,21 +426,22 @@ check_websafe_message_contents(struct sshkey *key,
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static void
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process_sign_request2(SocketEntry *e)
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{
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const u_char *data;
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u_char *signature = NULL;
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size_t dlen, slen = 0;
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size_t i, slen = 0;
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u_int compat = 0, flags;
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int r, ok = -1;
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char *fp = NULL;
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struct sshbuf *msg;
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struct sshbuf *msg = NULL, *data = NULL;
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struct sshkey *key = NULL;
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struct identity *id;
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struct notifier_ctx *notifier = NULL;
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if ((msg = sshbuf_new()) == NULL)
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debug_f("entering");
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if ((msg = sshbuf_new()) == NULL | (data = sshbuf_new()) == NULL)
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fatal_f("sshbuf_new failed");
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if ((r = sshkey_froms(e->request, &key)) != 0 ||
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(r = sshbuf_get_string_direct(e->request, &data, &dlen)) != 0 ||
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(r = sshbuf_get_stringb(e->request, data)) != 0 ||
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(r = sshbuf_get_u32(e->request, &flags)) != 0) {
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error_fr(r, "parse");
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goto send;
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@ -390,13 +451,13 @@ process_sign_request2(SocketEntry *e)
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verbose_f("%s key not found", sshkey_type(key));
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goto send;
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}
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if (id->confirm && confirm_key(id) != 0) {
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if (id->confirm && confirm_key(id, NULL) != 0) {
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verbose_f("user refused key");
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goto send;
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}
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if (sshkey_is_sk(id->key)) {
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if (strncmp(id->key->sk_application, "ssh:", 4) != 0 &&
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!check_websafe_message_contents(key, data, dlen)) {
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!check_websafe_message_contents(key, data)) {
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/* error already logged */
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goto send;
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}
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@ -411,7 +472,7 @@ process_sign_request2(SocketEntry *e)
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}
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/* XXX support PIN required FIDO keys */
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if ((r = sshkey_sign(id->key, &signature, &slen,
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data, dlen, agent_decode_alg(key, flags),
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sshbuf_ptr(data), sshbuf_len(data), agent_decode_alg(key, flags),
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id->sk_provider, NULL, compat)) != 0) {
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error_fr(r, "sshkey_sign");
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goto send;
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@ -420,8 +481,7 @@ process_sign_request2(SocketEntry *e)
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ok = 0;
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send:
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notify_complete(notifier, "User presence confirmed");
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sshkey_free(key);
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free(fp);
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if (ok == 0) {
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if ((r = sshbuf_put_u8(msg, SSH2_AGENT_SIGN_RESPONSE)) != 0 ||
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(r = sshbuf_put_string(msg, signature, slen)) != 0)
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@ -432,7 +492,10 @@ process_sign_request2(SocketEntry *e)
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if ((r = sshbuf_put_stringb(e->output, msg)) != 0)
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fatal_fr(r, "enqueue");
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sshbuf_free(data);
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sshbuf_free(msg);
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sshkey_free(key);
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free(fp);
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free(signature);
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}
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