1/* $OpenBSD: readpass.c,v 1.48 2010/12/15 00:49:27 djm 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#ifdef HAVE_PATHS_H
34# include <paths.h>
35#endif
36#include <signal.h>
37#include <stdarg.h>
38#include <stdio.h>
39#include <stdlib.h>
40#include <string.h>
41#include <unistd.h>
42
43#include "xmalloc.h"
44#include "misc.h"
45#include "pathnames.h"
46#include "log.h"
47#include "ssh.h"
48#include "uidswap.h"
49
50static char *
51ssh_askpass(char *askpass, const char *msg)
52{
53	pid_t pid, ret;
54	size_t len;
55	char *pass;
56	int p[2], status;
57	char buf[1024];
58	void (*osigchld)(int);
59
60	if (fflush(stdout) != 0)
61		error("ssh_askpass: fflush: %s", strerror(errno));
62	if (askpass == NULL)
63		fatal("internal error: askpass undefined");
64	if (pipe(p) < 0) {
65		error("ssh_askpass: pipe: %s", strerror(errno));
66		return NULL;
67	}
68	osigchld = signal(SIGCHLD, SIG_DFL);
69	if ((pid = fork()) < 0) {
70		error("ssh_askpass: fork: %s", strerror(errno));
71		signal(SIGCHLD, osigchld);
72		return NULL;
73	}
74	if (pid == 0) {
75		permanently_drop_suid(getuid());
76		close(p[0]);
77		if (dup2(p[1], STDOUT_FILENO) < 0)
78			fatal("ssh_askpass: dup2: %s", strerror(errno));
79		execlp(askpass, askpass, msg, (char *) 0);
80		fatal("ssh_askpass: exec(%s): %s", askpass, strerror(errno));
81	}
82	close(p[1]);
83
84	len = 0;
85	do {
86		ssize_t r = read(p[0], buf + len, sizeof(buf) - 1 - len);
87
88		if (r == -1 && errno == EINTR)
89			continue;
90		if (r <= 0)
91			break;
92		len += r;
93	} while (sizeof(buf) - 1 - len > 0);
94	buf[len] = '\0';
95
96	close(p[0]);
97	while ((ret = waitpid(pid, &status, 0)) < 0)
98		if (errno != EINTR)
99			break;
100	signal(SIGCHLD, osigchld);
101	if (ret == -1 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
102		memset(buf, 0, sizeof(buf));
103		return NULL;
104	}
105
106	buf[strcspn(buf, "\r\n")] = '\0';
107	pass = xstrdup(buf);
108	memset(buf, 0, sizeof(buf));
109	return pass;
110}
111
112/*
113 * Reads a passphrase from /dev/tty with echo turned off/on.  Returns the
114 * passphrase (allocated with xmalloc).  Exits if EOF is encountered. If
115 * RP_ALLOW_STDIN is set, the passphrase will be read from stdin if no
116 * tty is available
117 */
118char *
119read_passphrase(const char *prompt, int flags)
120{
121	char *askpass = NULL, *ret, buf[1024];
122	int rppflags, use_askpass = 0, ttyfd;
123
124	rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF;
125	if (flags & RP_USE_ASKPASS)
126		use_askpass = 1;
127	else if (flags & RP_ALLOW_STDIN) {
128		if (!isatty(STDIN_FILENO)) {
129			debug("read_passphrase: stdin is not a tty");
130			use_askpass = 1;
131		}
132	} else {
133		rppflags |= RPP_REQUIRE_TTY;
134		ttyfd = open(_PATH_TTY, O_RDWR);
135		if (ttyfd >= 0)
136			close(ttyfd);
137		else {
138			debug("read_passphrase: can't open %s: %s", _PATH_TTY,
139			    strerror(errno));
140			use_askpass = 1;
141		}
142	}
143
144	if ((flags & RP_USE_ASKPASS) && getenv("DISPLAY") == NULL)
145		return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");
146
147	if (use_askpass && getenv("DISPLAY")) {
148		if (getenv(SSH_ASKPASS_ENV))
149			askpass = getenv(SSH_ASKPASS_ENV);
150		else
151			askpass = _PATH_SSH_ASKPASS_DEFAULT;
152		if ((ret = ssh_askpass(askpass, prompt)) == NULL)
153			if (!(flags & RP_ALLOW_EOF))
154				return xstrdup("");
155		return ret;
156	}
157
158	if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) {
159		if (flags & RP_ALLOW_EOF)
160			return NULL;
161		return xstrdup("");
162	}
163
164	ret = xstrdup(buf);
165	memset(buf, 'x', sizeof buf);
166	return ret;
167}
168
169int
170ask_permission(const char *fmt, ...)
171{
172	va_list args;
173	char *p, prompt[1024];
174	int allowed = 0;
175
176	va_start(args, fmt);
177	vsnprintf(prompt, sizeof(prompt), fmt, args);
178	va_end(args);
179
180	p = read_passphrase(prompt, RP_USE_ASKPASS|RP_ALLOW_EOF);
181	if (p != NULL) {
182		/*
183		 * Accept empty responses and responses consisting
184		 * of the word "yes" as affirmative.
185		 */
186		if (*p == '\0' || *p == '\n' ||
187		    strcasecmp(p, "yes") == 0)
188			allowed = 1;
189		xfree(p);
190	}
191
192	return (allowed);
193}
194