xref: /openssh-portable/readpass.c (revision 4d28fa78)
1 /* $OpenBSD: readpass.c,v 1.54 2019/06/28 13:35:04 deraadt 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 
50 static char *
51 ssh_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) == -1) {
65 		error("ssh_askpass: pipe: %s", strerror(errno));
66 		return NULL;
67 	}
68 	osigchld = signal(SIGCHLD, SIG_DFL);
69 	if ((pid = fork()) == -1) {
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) == -1)
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)) == -1)
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  */
117 char *
118 read_passphrase(const char *prompt, int flags)
119 {
120 	char cr = '\r', *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 			/*
136 			 * If we're on a tty, ensure that show the prompt at
137 			 * the beginning of the line. This will hopefully
138 			 * clobber any password characters the user has
139 			 * optimistically typed before echo is disabled.
140 			 */
141 			(void)write(ttyfd, &cr, 1);
142 			close(ttyfd);
143 		} else {
144 			debug("read_passphrase: can't open %s: %s", _PATH_TTY,
145 			    strerror(errno));
146 			use_askpass = 1;
147 		}
148 	}
149 
150 	if ((flags & RP_USE_ASKPASS) && getenv("DISPLAY") == NULL)
151 		return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");
152 
153 	if (use_askpass && getenv("DISPLAY")) {
154 		if (getenv(SSH_ASKPASS_ENV))
155 			askpass = getenv(SSH_ASKPASS_ENV);
156 		else
157 			askpass = _PATH_SSH_ASKPASS_DEFAULT;
158 		if ((ret = ssh_askpass(askpass, prompt)) == NULL)
159 			if (!(flags & RP_ALLOW_EOF))
160 				return xstrdup("");
161 		return ret;
162 	}
163 
164 	if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) {
165 		if (flags & RP_ALLOW_EOF)
166 			return NULL;
167 		return xstrdup("");
168 	}
169 
170 	ret = xstrdup(buf);
171 	explicit_bzero(buf, sizeof(buf));
172 	return ret;
173 }
174 
175 int
176 ask_permission(const char *fmt, ...)
177 {
178 	va_list args;
179 	char *p, prompt[1024];
180 	int allowed = 0;
181 
182 	va_start(args, fmt);
183 	vsnprintf(prompt, sizeof(prompt), fmt, args);
184 	va_end(args);
185 
186 	p = read_passphrase(prompt, RP_USE_ASKPASS|RP_ALLOW_EOF);
187 	if (p != NULL) {
188 		/*
189 		 * Accept empty responses and responses consisting
190 		 * of the word "yes" as affirmative.
191 		 */
192 		if (*p == '\0' || *p == '\n' ||
193 		    strcasecmp(p, "yes") == 0)
194 			allowed = 1;
195 		free(p);
196 	}
197 
198 	return (allowed);
199 }
200