Annotation of src/usr.bin/ssh/ssh-sk-helper.c, Revision 1.3
1.3 ! markus 1: /* $OpenBSD: ssh-sk-helper.c,v 1.2 2019/11/12 19:30:50 markus Exp $ */
1.1 djm 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 <stdarg.h>
34: #include <stdio.h>
35: #include <stdlib.h>
36: #include <string.h>
37: #include <unistd.h>
38: #include <errno.h>
39:
40: #include "xmalloc.h"
41: #include "log.h"
42: #include "sshkey.h"
43: #include "authfd.h"
44: #include "misc.h"
45: #include "sshbuf.h"
46: #include "msg.h"
47: #include "uidswap.h"
48: #include "sshkey.h"
49: #include "ssherr.h"
50: #include "ssh-sk.h"
51:
52: extern char *__progname;
53:
54: int
55: main(int argc, char **argv)
56: {
57: SyslogFacility log_facility = SYSLOG_FACILITY_AUTH;
58: LogLevel log_level = SYSLOG_LEVEL_ERROR;
59: struct sshbuf *req, *resp, *kbuf;
60: struct sshkey *key;
61: uint32_t compat;
62: const u_char *message;
63: u_char version, *sig;
64: size_t msglen, siglen;
65: char *provider;
66: int in, out, ch, r, log_stderr = 0;
67:
68: sanitise_stdfd();
69: log_init(__progname, log_level, log_facility, log_stderr);
70:
71: while ((ch = getopt(argc, argv, "v")) != -1) {
72: switch (ch) {
73: case 'v':
74: log_stderr = 1;
75: if (log_level == SYSLOG_LEVEL_ERROR)
76: log_level = SYSLOG_LEVEL_DEBUG1;
77: else if (log_level < SYSLOG_LEVEL_DEBUG3)
78: log_level++;
79: break;
80: default:
81: fprintf(stderr, "usage: %s [-v]\n", __progname);
82: exit(1);
83: }
84: }
85: log_init(__progname, log_level, log_facility, log_stderr);
86:
87: /*
88: * Rearrange our file descriptors a little; we don't trust the
89: * providers not to fiddle with stdin/out.
90: */
91: closefrom(STDERR_FILENO + 1);
92: if ((in = dup(STDIN_FILENO)) == -1 || (out = dup(STDOUT_FILENO)) == -1)
93: fatal("%s: dup: %s", __progname, strerror(errno));
94: close(STDIN_FILENO);
95: close(STDOUT_FILENO);
96: sanitise_stdfd(); /* resets to /dev/null */
97:
98: if ((req = sshbuf_new()) == NULL || (resp = sshbuf_new()) == NULL)
99: fatal("%s: sshbuf_new failed", __progname);
100: if (ssh_msg_recv(in, req) < 0)
101: fatal("ssh_msg_recv failed");
102: close(in);
103: debug("%s: received message len %zu", __progname, sshbuf_len(req));
104:
105: if ((r = sshbuf_get_u8(req, &version)) != 0)
106: fatal("%s: buffer error: %s", __progname, ssh_err(r));
107: if (version != SSH_SK_HELPER_VERSION) {
108: fatal("unsupported version: received %d, expected %d",
109: version, SSH_SK_HELPER_VERSION);
110: }
111: if ((r = sshbuf_froms(req, &kbuf)) != 0 ||
112: (r = sshkey_private_deserialize(kbuf, &key)) != 0)
113: fatal("Unable to parse key: %s", ssh_err(r));
1.3 ! markus 114: if (!sshkey_is_sk(key))
1.1 djm 115: fatal("Unsupported key type %s", sshkey_ssh_name(key));
116:
117: if ((r = sshbuf_get_cstring(req, &provider, NULL)) != 0 ||
118: (r = sshbuf_get_string_direct(req, &message, &msglen)) != 0 ||
119: (r = sshbuf_get_u32(req, &compat)) != 0)
120: fatal("%s: buffer error: %s", __progname, ssh_err(r));
121: if (sshbuf_len(req) != 0)
122: fatal("%s: trailing data in request", __progname);
123:
124: debug("%s: ready to sign with key %s, provider %s: "
125: "msg len %zu, compat 0x%lx", __progname, sshkey_type(key),
126: provider, msglen, (u_long)compat);
127:
1.2 markus 128: if ((r = sshsk_sign(provider, key, &sig, &siglen,
1.1 djm 129: message, msglen, compat)) != 0)
130: fatal("Signing failed: %s", ssh_err(r));
131:
132: /* send reply */
133: if ((r = sshbuf_put_string(resp, sig, siglen)) != 0)
134: fatal("%s: buffer error: %s", __progname, ssh_err(r));
135: debug("%s: reply len %zu", __progname, sshbuf_len(resp));
136: if (ssh_msg_send(out, SSH_SK_HELPER_VERSION, resp) == -1)
137: fatal("ssh_msg_send failed");
138: close(out);
139:
140: return (0);
141: }
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