xref: /openssh-portable/ssh-sk-helper.c (revision 2c55744a)
1 /* $OpenBSD: ssh-sk-helper.c,v 1.3 2019/11/12 19:33:08 markus 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 #ifdef ENABLE_SK
55 extern char *__progname;
56 
57 int
58 main(int argc, char **argv)
59 {
60 	SyslogFacility log_facility = SYSLOG_FACILITY_AUTH;
61 	LogLevel log_level = SYSLOG_LEVEL_ERROR;
62 	struct sshbuf *req, *resp, *kbuf;
63 	struct sshkey *key;
64 	uint32_t compat;
65 	const u_char *message;
66 	u_char version, *sig;
67 	size_t msglen, siglen;
68 	char *provider;
69 	int in, out, ch, r, log_stderr = 0;
70 
71 	sanitise_stdfd();
72 	log_init(__progname, log_level, log_facility, log_stderr);
73 
74 	while ((ch = getopt(argc, argv, "v")) != -1) {
75 		switch (ch) {
76 		case 'v':
77 			log_stderr = 1;
78 			if (log_level == SYSLOG_LEVEL_ERROR)
79 				log_level = SYSLOG_LEVEL_DEBUG1;
80 			else if (log_level < SYSLOG_LEVEL_DEBUG3)
81 				log_level++;
82 			break;
83 		default:
84 			fprintf(stderr, "usage: %s [-v]\n", __progname);
85 			exit(1);
86 		}
87 	}
88 	log_init(__progname, log_level, log_facility, log_stderr);
89 
90 	/*
91 	 * Rearrange our file descriptors a little; we don't trust the
92 	 * providers not to fiddle with stdin/out.
93 	 */
94 	closefrom(STDERR_FILENO + 1);
95 	if ((in = dup(STDIN_FILENO)) == -1 || (out = dup(STDOUT_FILENO)) == -1)
96 		fatal("%s: dup: %s", __progname, strerror(errno));
97 	close(STDIN_FILENO);
98 	close(STDOUT_FILENO);
99 	sanitise_stdfd(); /* resets to /dev/null */
100 
101 	if ((req = sshbuf_new()) == NULL || (resp = sshbuf_new()) == NULL)
102 		fatal("%s: sshbuf_new failed", __progname);
103 	if (ssh_msg_recv(in, req) < 0)
104 		fatal("ssh_msg_recv failed");
105 	close(in);
106 	debug("%s: received message len %zu", __progname, sshbuf_len(req));
107 
108 	if ((r = sshbuf_get_u8(req, &version)) != 0)
109 		fatal("%s: buffer error: %s", __progname, ssh_err(r));
110 	if (version != SSH_SK_HELPER_VERSION) {
111 		fatal("unsupported version: received %d, expected %d",
112 		    version, SSH_SK_HELPER_VERSION);
113 	}
114 	if ((r = sshbuf_froms(req, &kbuf)) != 0 ||
115 	    (r = sshkey_private_deserialize(kbuf, &key)) != 0)
116 		fatal("Unable to parse key: %s", ssh_err(r));
117 	if (!sshkey_is_sk(key))
118 		fatal("Unsupported key type %s", sshkey_ssh_name(key));
119 
120 	if ((r = sshbuf_get_cstring(req, &provider, NULL)) != 0 ||
121 	    (r = sshbuf_get_string_direct(req, &message, &msglen)) != 0 ||
122 	    (r = sshbuf_get_u32(req, &compat)) != 0)
123 		fatal("%s: buffer error: %s", __progname, ssh_err(r));
124 	if (sshbuf_len(req) != 0)
125 		fatal("%s: trailing data in request", __progname);
126 
127 	debug("%s: ready to sign with key %s, provider %s: "
128 	    "msg len %zu, compat 0x%lx", __progname, sshkey_type(key),
129 	    provider, msglen, (u_long)compat);
130 
131 	if ((r = sshsk_sign(provider, key, &sig, &siglen,
132 	    message, msglen, compat)) != 0)
133 		fatal("Signing failed: %s", ssh_err(r));
134 
135 	/* send reply */
136 	if ((r = sshbuf_put_string(resp, sig, siglen)) != 0)
137 		fatal("%s: buffer error: %s", __progname, ssh_err(r));
138 	debug("%s: reply len %zu", __progname, sshbuf_len(resp));
139 	if (ssh_msg_send(out, SSH_SK_HELPER_VERSION, resp) == -1)
140 		fatal("ssh_msg_send failed");
141 	close(out);
142 
143 	return (0);
144 }
145 #else /* ENABLE_SK */
146 #include <stdio.h>
147 
148 int
149 main(int argc, char **argv)
150 {
151 	fprintf(stderr, "ssh-sk-helper: disabled at compile time\n");
152 	return -1;
153 }
154 #endif /* ENABLE_SK */
155