diff options
Diffstat (limited to 'ssh-agent.c')
| -rw-r--r-- | ssh-agent.c | 110 |
1 files changed, 100 insertions, 10 deletions
diff --git a/ssh-agent.c b/ssh-agent.c index e081413b..effffffe 100644 --- a/ssh-agent.c +++ b/ssh-agent.c @@ -1,4 +1,4 @@ -/* $OpenBSD: ssh-agent.c,v 1.257 2020/03/06 18:28:27 markus Exp $ */ +/* $OpenBSD: ssh-agent.c,v 1.258 2020/05/26 01:26:58 djm Exp $ */ /* * Author: Tatu Ylonen <ylo@cs.hut.fi> * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland @@ -77,6 +77,7 @@ #include "xmalloc.h" #include "ssh.h" +#include "ssh2.h" #include "sshbuf.h" #include "sshkey.h" #include "authfd.h" @@ -167,6 +168,9 @@ static long lifetime = 0; static int fingerprint_hash = SSH_FP_HASH_DEFAULT; +/* Refuse signing of non-SSH messages for web-origin FIDO keys */ +static int restrict_websafe = 1; + static void close_socket(SocketEntry *e) { @@ -282,6 +286,80 @@ agent_decode_alg(struct sshkey *key, u_int flags) return NULL; } +/* + * 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, + const u_char *msg, size_t len) +{ + int matched = 0; + struct sshbuf *b; + u_char m, n; + char *cp1 = NULL, *cp2 = NULL; + int r; + struct sshkey *mkey = NULL; + + if ((b = sshbuf_from(msg, len)) == NULL) + fatal("%s: sshbuf_new", __func__); + + /* 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("%s: parsed userauth", __func__); + if (m == SSH2_MSG_USERAUTH_REQUEST && n == 1 && + strcmp(cp1, "ssh-connection") == 0 && + strcmp(cp2, "publickey") == 0 && + sshkey_equal(key, mkey)) { + debug("%s: well formed userauth", __func__); + matched = 1; + } + } + free(cp1); + free(cp2); + sshkey_free(mkey); + sshbuf_free(b); + if (matched) + return 1; + + if ((b = sshbuf_from(msg, len)) == NULL) + fatal("%s: sshbuf_new", __func__); + 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("%s: parsed sshsig", __func__); + matched = 1; + } + + sshbuf_free(b); + if (matched) + return 1; + + /* XXX CA signature operation */ + + error("web-origin key attempting to sign non-SSH message"); + return 0; +} + /* ssh2 only */ static void process_sign_request2(SocketEntry *e) @@ -314,14 +392,20 @@ process_sign_request2(SocketEntry *e) verbose("%s: user refused key", __func__); goto send; } - if (sshkey_is_sk(id->key) && - (id->key->sk_flags & SSH_SK_USER_PRESENCE_REQD)) { - if ((fp = sshkey_fingerprint(key, SSH_FP_HASH_DEFAULT, - SSH_FP_DEFAULT)) == NULL) - fatal("%s: fingerprint failed", __func__); - notifier = notify_start(0, - "Confirm user presence for key %s %s", - sshkey_type(id->key), fp); + if (sshkey_is_sk(id->key)) { + if (strncmp(id->key->sk_application, "ssh:", 4) != 0 && + !check_websafe_message_contents(key, data, dlen)) { + /* error already logged */ + goto send; + } + if ((id->key->sk_flags & SSH_SK_USER_PRESENCE_REQD)) { + if ((fp = sshkey_fingerprint(key, SSH_FP_HASH_DEFAULT, + SSH_FP_DEFAULT)) == NULL) + fatal("%s: fingerprint failed", __func__); + notifier = notify_start(0, + "Confirm user presence for key %s %s", + sshkey_type(id->key), fp); + } } if ((r = sshkey_sign(id->key, &signature, &slen, data, dlen, agent_decode_alg(key, flags), @@ -1212,7 +1296,7 @@ main(int ac, char **av) __progname = ssh_get_progname(av[0]); seed_rng(); - while ((ch = getopt(ac, av, "cDdksE:a:P:t:")) != -1) { + while ((ch = getopt(ac, av, "cDdksE:a:O:P:t:")) != -1) { switch (ch) { case 'E': fingerprint_hash = ssh_digest_alg_by_name(optarg); @@ -1227,6 +1311,12 @@ main(int ac, char **av) case 'k': k_flag++; break; + case 'O': + if (strcmp(optarg, "no-restrict-websafe") == 0) + restrict_websafe = 0; + else + fatal("Unknown -O option"); + break; case 'P': if (provider_whitelist != NULL) fatal("-P option already specified"); |