xref: /openssh-portable/ssh-sk-helper.c (revision 07da39f7)
1 /* $OpenBSD: ssh-sk-helper.c,v 1.1 2019/10/31 21:22:01 djm Exp $ */
2 /*
3  * Copyright (c) 2019 Google LLC
4  *
5  * Permission to use, copy, modify, and distribute this software for any
6  * purpose with or without fee is hereby granted, provided that the above
7  * copyright notice and this permission notice appear in all copies.
8  *
9  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16  */
17 
18 /*
19  * This is a tiny program used to isolate the address space used for
20  * security key middleware signing operations from ssh-agent. It is similar
21  * to ssh-pkcs11-helper.c but considerably simpler as the signing operation
22  * for this case are stateless.
23  *
24  * It receives a signing request (key, provider, message, flags) from
25  * stdin, attempts to perform a signature using the security key provider
26  * and returns the resultant signature via stdout.
27  *
28  * In the future, this program might gain additional functions to support
29  * FIDO2 tokens such as enumerating resident keys. When this happens it will
30  * be necessary to crank SSH_SK_HELPER_VERSION below.
31  */
32 
33 #include "includes.h"
34 
35 #include <stdarg.h>
36 #include <stdio.h>
37 #include <stdlib.h>
38 #include <string.h>
39 #include <unistd.h>
40 #include <errno.h>
41 
42 #include "xmalloc.h"
43 #include "log.h"
44 #include "sshkey.h"
45 #include "authfd.h"
46 #include "misc.h"
47 #include "sshbuf.h"
48 #include "msg.h"
49 #include "uidswap.h"
50 #include "sshkey.h"
51 #include "ssherr.h"
52 #include "ssh-sk.h"
53 
54 extern char *__progname;
55 
56 int
57 main(int argc, char **argv)
58 {
59 	SyslogFacility log_facility = SYSLOG_FACILITY_AUTH;
60 	LogLevel log_level = SYSLOG_LEVEL_ERROR;
61 	struct sshbuf *req, *resp, *kbuf;
62 	struct sshkey *key;
63 	uint32_t compat;
64 	const u_char *message;
65 	u_char version, *sig;
66 	size_t msglen, siglen;
67 	char *provider;
68 	int in, out, ch, r, log_stderr = 0;
69 
70 	sanitise_stdfd();
71 	log_init(__progname, log_level, log_facility, log_stderr);
72 
73 	while ((ch = getopt(argc, argv, "v")) != -1) {
74 		switch (ch) {
75 		case 'v':
76 			log_stderr = 1;
77 			if (log_level == SYSLOG_LEVEL_ERROR)
78 				log_level = SYSLOG_LEVEL_DEBUG1;
79 			else if (log_level < SYSLOG_LEVEL_DEBUG3)
80 				log_level++;
81 			break;
82 		default:
83 			fprintf(stderr, "usage: %s [-v]\n", __progname);
84 			exit(1);
85 		}
86 	}
87 	log_init(__progname, log_level, log_facility, log_stderr);
88 
89 	/*
90 	 * Rearrange our file descriptors a little; we don't trust the
91 	 * providers not to fiddle with stdin/out.
92 	 */
93 	closefrom(STDERR_FILENO + 1);
94 	if ((in = dup(STDIN_FILENO)) == -1 || (out = dup(STDOUT_FILENO)) == -1)
95 		fatal("%s: dup: %s", __progname, strerror(errno));
96 	close(STDIN_FILENO);
97 	close(STDOUT_FILENO);
98 	sanitise_stdfd(); /* resets to /dev/null */
99 
100 	if ((req = sshbuf_new()) == NULL || (resp = sshbuf_new()) == NULL)
101 		fatal("%s: sshbuf_new failed", __progname);
102 	if (ssh_msg_recv(in, req) < 0)
103 		fatal("ssh_msg_recv failed");
104 	close(in);
105 	debug("%s: received message len %zu", __progname, sshbuf_len(req));
106 
107 	if ((r = sshbuf_get_u8(req, &version)) != 0)
108 		fatal("%s: buffer error: %s", __progname, ssh_err(r));
109 	if (version != SSH_SK_HELPER_VERSION) {
110 		fatal("unsupported version: received %d, expected %d",
111 		    version, SSH_SK_HELPER_VERSION);
112 	}
113 	if ((r = sshbuf_froms(req, &kbuf)) != 0 ||
114 	    (r = sshkey_private_deserialize(kbuf, &key)) != 0)
115 		fatal("Unable to parse key: %s", ssh_err(r));
116 	if (sshkey_type_plain(key->type) != KEY_ECDSA_SK)
117 		fatal("Unsupported key type %s", sshkey_ssh_name(key));
118 
119 	if ((r = sshbuf_get_cstring(req, &provider, NULL)) != 0 ||
120 	    (r = sshbuf_get_string_direct(req, &message, &msglen)) != 0 ||
121 	    (r = sshbuf_get_u32(req, &compat)) != 0)
122 		fatal("%s: buffer error: %s", __progname, ssh_err(r));
123 	if (sshbuf_len(req) != 0)
124 		fatal("%s: trailing data in request", __progname);
125 
126 	debug("%s: ready to sign with key %s, provider %s: "
127 	    "msg len %zu, compat 0x%lx", __progname, sshkey_type(key),
128 	    provider, msglen, (u_long)compat);
129 
130 	if ((r = sshsk_ecdsa_sign(provider, key, &sig, &siglen,
131 	    message, msglen, compat)) != 0)
132 		fatal("Signing failed: %s", ssh_err(r));
133 
134 	/* send reply */
135 	if ((r = sshbuf_put_string(resp, sig, siglen)) != 0)
136 		fatal("%s: buffer error: %s", __progname, ssh_err(r));
137 	debug("%s: reply len %zu", __progname, sshbuf_len(resp));
138 	if (ssh_msg_send(out, SSH_SK_HELPER_VERSION, resp) == -1)
139 		fatal("ssh_msg_send failed");
140 	close(out);
141 
142 	return (0);
143 }
144