readpass.c revision 1.46 
1/* $OpenBSD: readpass.c,v 1.46 2006/08/01 23:22:47 stevesk Exp $ */
2/*
3 * Copyright (c) 2001 Markus Friedl.  All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#include "includes.h"
27
28#include <sys/types.h>
29#include <sys/wait.h>
30
31#include <errno.h>
32#include <fcntl.h>
33#include <paths.h>
34#include <readpassphrase.h>
35#include <stdarg.h>
36#include <stdio.h>
37#include <stdlib.h>
38#include <string.h>
39#include <unistd.h>
40
41#include "xmalloc.h"
42#include "misc.h"
43#include "pathnames.h"
44#include "log.h"
45#include "ssh.h"
46#include "uidswap.h"
47
48static char *
49ssh_askpass(char *askpass, const char *msg)
50{
51	pid_t pid;
52	size_t len;
53	char *pass;
54	int p[2], status, ret;
55	char buf[1024];
56
57	if (fflush(stdout) != 0)
58		error("ssh_askpass: fflush: %s", strerror(errno));
59	if (askpass == NULL)
60		fatal("internal error: askpass undefined");
61	if (pipe(p) < 0) {
62		error("ssh_askpass: pipe: %s", strerror(errno));
63		return NULL;
64	}
65	if ((pid = fork()) < 0) {
66		error("ssh_askpass: fork: %s", strerror(errno));
67		return NULL;
68	}
69	if (pid == 0) {
70		permanently_drop_suid(getuid());
71		close(p[0]);
72		if (dup2(p[1], STDOUT_FILENO) < 0)
73			fatal("ssh_askpass: dup2: %s", strerror(errno));
74		execlp(askpass, askpass, msg, (char *) 0);
75		fatal("ssh_askpass: exec(%s): %s", askpass, strerror(errno));
76	}
77	close(p[1]);
78
79	len = ret = 0;
80	do {
81		ret = read(p[0], buf + len, sizeof(buf) - 1 - len);
82		if (ret == -1 && errno == EINTR)
83			continue;
84		if (ret <= 0)
85			break;
86		len += ret;
87	} while (sizeof(buf) - 1 - len > 0);
88	buf[len] = '\0';
89
90	close(p[0]);
91	while (waitpid(pid, &status, 0) < 0)
92		if (errno != EINTR)
93			break;
94
95	if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
96		memset(buf, 0, sizeof(buf));
97		return NULL;
98	}
99
100	buf[strcspn(buf, "\r\n")] = '\0';
101	pass = xstrdup(buf);
102	memset(buf, 0, sizeof(buf));
103	return pass;
104}
105
106/*
107 * Reads a passphrase from /dev/tty with echo turned off/on.  Returns the
108 * passphrase (allocated with xmalloc).  Exits if EOF is encountered. If
109 * RP_ALLOW_STDIN is set, the passphrase will be read from stdin if no
110 * tty is available
111 */
112char *
113read_passphrase(const char *prompt, int flags)
114{
115	char *askpass = NULL, *ret, buf[1024];
116	int rppflags, use_askpass = 0, ttyfd;
117
118	rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF;
119	if (flags & RP_USE_ASKPASS)
120		use_askpass = 1;
121	else if (flags & RP_ALLOW_STDIN) {
122		if (!isatty(STDIN_FILENO)) {
123			debug("read_passphrase: stdin is not a tty");
124			use_askpass = 1;
125		}
126	} else {
127		rppflags |= RPP_REQUIRE_TTY;
128		ttyfd = open(_PATH_TTY, O_RDWR);
129		if (ttyfd >= 0)
130			close(ttyfd);
131		else {
132			debug("read_passphrase: can't open %s: %s", _PATH_TTY,
133			    strerror(errno));
134			use_askpass = 1;
135		}
136	}
137
138	if ((flags & RP_USE_ASKPASS) && getenv("DISPLAY") == NULL)
139		return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");
140
141	if (use_askpass && getenv("DISPLAY")) {
142		if (getenv(SSH_ASKPASS_ENV))
143			askpass = getenv(SSH_ASKPASS_ENV);
144		else
145			askpass = _PATH_SSH_ASKPASS_DEFAULT;
146		if ((ret = ssh_askpass(askpass, prompt)) == NULL)
147			if (!(flags & RP_ALLOW_EOF))
148				return xstrdup("");
149		return ret;
150	}
151
152	if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) {
153		if (flags & RP_ALLOW_EOF)
154			return NULL;
155		return xstrdup("");
156	}
157
158	ret = xstrdup(buf);
159	memset(buf, 'x', sizeof buf);
160	return ret;
161}
162
163int
164ask_permission(const char *fmt, ...)
165{
166	va_list args;
167	char *p, prompt[1024];
168	int allowed = 0;
169
170	va_start(args, fmt);
171	vsnprintf(prompt, sizeof(prompt), fmt, args);
172	va_end(args);
173
174	p = read_passphrase(prompt, RP_USE_ASKPASS|RP_ALLOW_EOF);
175	if (p != NULL) {
176		/*
177		 * Accept empty responses and responses consisting
178		 * of the word "yes" as affirmative.
179		 */
180		if (*p == '\0' || *p == '\n' ||
181		    strcasecmp(p, "yes") == 0)
182			allowed = 1;
183		xfree(p);
184	}
185
186	return (allowed);
187}
188