1/* $OpenBSD: readpass.c,v 1.52 2018/07/18 11:34:04 dtucker 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		close(p[0]);
76		if (dup2(p[1], STDOUT_FILENO) < 0)
77			fatal("ssh_askpass: dup2: %s", strerror(errno));
78		execlp(askpass, askpass, msg, (char *)NULL);
79		fatal("ssh_askpass: exec(%s): %s", askpass, strerror(errno));
80	}
81	close(p[1]);
82
83	len = 0;
84	do {
85		ssize_t r = read(p[0], buf + len, sizeof(buf) - 1 - len);
86
87		if (r == -1 && errno == EINTR)
88			continue;
89		if (r <= 0)
90			break;
91		len += r;
92	} while (sizeof(buf) - 1 - len > 0);
93	buf[len] = '\0';
94
95	close(p[0]);
96	while ((ret = waitpid(pid, &status, 0)) < 0)
97		if (errno != EINTR)
98			break;
99	signal(SIGCHLD, osigchld);
100	if (ret == -1 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
101		explicit_bzero(buf, sizeof(buf));
102		return NULL;
103	}
104
105	buf[strcspn(buf, "\r\n")] = '\0';
106	pass = xstrdup(buf);
107	explicit_bzero(buf, sizeof(buf));
108	return pass;
109}
110
111/*
112 * Reads a passphrase from /dev/tty with echo turned off/on.  Returns the
113 * passphrase (allocated with xmalloc).  Exits if EOF is encountered. If
114 * RP_ALLOW_STDIN is set, the passphrase will be read from stdin if no
115 * tty is available
116 */
117char *
118read_passphrase(const char *prompt, int flags)
119{
120	char *askpass = NULL, *ret, buf[1024];
121	int rppflags, use_askpass = 0, ttyfd;
122
123	rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF;
124	if (flags & RP_USE_ASKPASS)
125		use_askpass = 1;
126	else if (flags & RP_ALLOW_STDIN) {
127		if (!isatty(STDIN_FILENO)) {
128			debug("read_passphrase: stdin is not a tty");
129			use_askpass = 1;
130		}
131	} else {
132		rppflags |= RPP_REQUIRE_TTY;
133		ttyfd = open(_PATH_TTY, O_RDWR);
134		if (ttyfd >= 0)
135			close(ttyfd);
136		else {
137			debug("read_passphrase: can't open %s: %s", _PATH_TTY,
138			    strerror(errno));
139			use_askpass = 1;
140		}
141	}
142
143	if ((flags & RP_USE_ASKPASS) && getenv("DISPLAY") == NULL)
144		return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");
145
146	if (use_askpass && getenv("DISPLAY")) {
147		if (getenv(SSH_ASKPASS_ENV))
148			askpass = getenv(SSH_ASKPASS_ENV);
149		else
150			askpass = _PATH_SSH_ASKPASS_DEFAULT;
151		if ((ret = ssh_askpass(askpass, prompt)) == NULL)
152			if (!(flags & RP_ALLOW_EOF))
153				return xstrdup("");
154		return ret;
155	}
156
157	if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) {
158		if (flags & RP_ALLOW_EOF)
159			return NULL;
160		return xstrdup("");
161	}
162
163	ret = xstrdup(buf);
164	explicit_bzero(buf, sizeof(buf));
165	return ret;
166}
167
168int
169ask_permission(const char *fmt, ...)
170{
171	va_list args;
172	char *p, prompt[1024];
173	int allowed = 0;
174
175	va_start(args, fmt);
176	vsnprintf(prompt, sizeof(prompt), fmt, args);
177	va_end(args);
178
179	p = read_passphrase(prompt, RP_USE_ASKPASS|RP_ALLOW_EOF);
180	if (p != NULL) {
181		/*
182		 * Accept empty responses and responses consisting
183		 * of the word "yes" as affirmative.
184		 */
185		if (*p == '\0' || *p == '\n' ||
186		    strcasecmp(p, "yes") == 0)
187			allowed = 1;
188		free(p);
189	}
190
191	return (allowed);
192}
193