xref: /openssh-portable/readpass.c (revision 106079c0)
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 
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) < 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  */
118 char *
119 read_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 
169 int
170 ask_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