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Diffstat (limited to 'ssh-agent.c')
-rw-r--r--ssh-agent.c158
1 files changed, 129 insertions, 29 deletions
diff --git a/ssh-agent.c b/ssh-agent.c
index e081413b8154..e1fd1f3f689a 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 1.264 2020/09/18 08:16:38 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"
@@ -92,8 +93,8 @@
#include "ssh-pkcs11.h"
#include "sk-api.h"
-#ifndef DEFAULT_PROVIDER_WHITELIST
-# define DEFAULT_PROVIDER_WHITELIST "/usr/lib*/*,/usr/local/lib*/*"
+#ifndef DEFAULT_ALLOWED_PROVIDERS
+# define DEFAULT_ALLOWED_PROVIDERS "/usr/lib*/*,/usr/local/lib*/*"
#endif
/* Maximum accepted message length */
@@ -149,8 +150,8 @@ pid_t cleanup_pid = 0;
char socket_name[PATH_MAX];
char socket_dir[PATH_MAX];
-/* PKCS#11/Security key path whitelist */
-static char *provider_whitelist;
+/* Pattern-list of allowed PKCS#11/Security key paths */
+static char *allowed_providers;
/* locking */
#define LOCK_SIZE 32
@@ -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)
@@ -314,18 +392,25 @@ 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);
+ }
}
+ /* XXX support PIN required FIDO keys */
if ((r = sshkey_sign(id->key, &signature, &slen,
data, dlen, agent_decode_alg(key, flags),
- id->sk_provider, compat)) != 0) {
+ id->sk_provider, NULL, compat)) != 0) {
error("%s: sshkey_sign: %s", __func__, ssh_err(r));
goto send;
}
@@ -528,9 +613,9 @@ process_add_identity(SocketEntry *e)
free(sk_provider);
sk_provider = xstrdup(canonical_provider);
if (match_pattern_list(sk_provider,
- provider_whitelist, 0) != 1) {
+ allowed_providers, 0) != 1) {
error("Refusing add key: "
- "provider %s not whitelisted", sk_provider);
+ "provider %s not allowed", sk_provider);
free(sk_provider);
goto send;
}
@@ -685,9 +770,9 @@ process_add_smartcard_key(SocketEntry *e)
provider, strerror(errno));
goto send;
}
- if (match_pattern_list(canonical_provider, provider_whitelist, 0) != 1) {
+ if (match_pattern_list(canonical_provider, allowed_providers, 0) != 1) {
verbose("refusing PKCS#11 add of \"%.100s\": "
- "provider not whitelisted", canonical_provider);
+ "provider not allowed", canonical_provider);
goto send;
}
debug("%s: add %.100s", __func__, canonical_provider);
@@ -767,8 +852,10 @@ send:
}
#endif /* ENABLE_PKCS11 */
-/* dispatch incoming messages */
-
+/*
+ * dispatch incoming message.
+ * returns 1 on success, 0 for incomplete messages or -1 on error.
+ */
static int
process_message(u_int socknum)
{
@@ -822,7 +909,7 @@ process_message(u_int socknum)
/* send a fail message for all other request types */
send_status(e, 0);
}
- return 0;
+ return 1;
}
switch (type) {
@@ -866,7 +953,7 @@ process_message(u_int socknum)
send_status(e, 0);
break;
}
- return 0;
+ return 1;
}
static void
@@ -957,7 +1044,12 @@ handle_conn_read(u_int socknum)
if ((r = sshbuf_put(sockets[socknum].input, buf, len)) != 0)
fatal("%s: buffer error: %s", __func__, ssh_err(r));
explicit_bzero(buf, sizeof(buf));
- process_message(socknum);
+ for (;;) {
+ if ((r = process_message(socknum)) == -1)
+ return -1;
+ else if (r == 0)
+ break;
+ }
return 0;
}
@@ -1170,7 +1262,9 @@ usage(void)
{
fprintf(stderr,
"usage: ssh-agent [-c | -s] [-Dd] [-a bind_address] [-E fingerprint_hash]\n"
- " [-P provider_whitelist] [-t life] [command [arg ...]]\n"
+ " [-P allowed_providers] [-t life]\n"
+ " ssh-agent [-a bind_address] [-E fingerprint_hash] [-P allowed_providers]\n"
+ " [-t life] command [arg ...]\n"
" ssh-agent [-c | -s] -k\n");
exit(1);
}
@@ -1212,7 +1306,7 @@ 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);
@@ -1227,10 +1321,16 @@ 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)
+ if (allowed_providers != NULL)
fatal("-P option already specified");
- provider_whitelist = xstrdup(optarg);
+ allowed_providers = xstrdup(optarg);
break;
case 's':
if (c_flag)
@@ -1266,8 +1366,8 @@ main(int ac, char **av)
if (ac > 0 && (c_flag || k_flag || s_flag || d_flag || D_flag))
usage();
- if (provider_whitelist == NULL)
- provider_whitelist = xstrdup(DEFAULT_PROVIDER_WHITELIST);
+ if (allowed_providers == NULL)
+ allowed_providers = xstrdup(DEFAULT_ALLOWED_PROVIDERS);
if (ac == 0 && !c_flag && !s_flag) {
shell = getenv("SHELL");
generated by cgit v1.3 (git 2.53.0) at 2026-04-18 16:10:00 +0000