xref: /openssh-portable/readpass.c (revision e3476ed0)
1 /* $OpenBSD: readpass.c,v 1.44 2006/07/22 20:48:23 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 #ifdef HAVE_PATHS_H
34 # include <paths.h>
35 #endif
36 #include <stdarg.h>
37 #include <string.h>
38 #include <unistd.h>
39 
40 #include "xmalloc.h"
41 #include "misc.h"
42 #include "pathnames.h"
43 #include "log.h"
44 #include "ssh.h"
45 #include "uidswap.h"
46 
47 static char *
48 ssh_askpass(char *askpass, const char *msg)
49 {
50 	pid_t pid;
51 	size_t len;
52 	char *pass;
53 	int p[2], status, ret;
54 	char buf[1024];
55 
56 	if (fflush(stdout) != 0)
57 		error("ssh_askpass: fflush: %s", strerror(errno));
58 	if (askpass == NULL)
59 		fatal("internal error: askpass undefined");
60 	if (pipe(p) < 0) {
61 		error("ssh_askpass: pipe: %s", strerror(errno));
62 		return NULL;
63 	}
64 	if ((pid = fork()) < 0) {
65 		error("ssh_askpass: fork: %s", strerror(errno));
66 		return NULL;
67 	}
68 	if (pid == 0) {
69 		permanently_drop_suid(getuid());
70 		close(p[0]);
71 		if (dup2(p[1], STDOUT_FILENO) < 0)
72 			fatal("ssh_askpass: dup2: %s", strerror(errno));
73 		execlp(askpass, askpass, msg, (char *) 0);
74 		fatal("ssh_askpass: exec(%s): %s", askpass, strerror(errno));
75 	}
76 	close(p[1]);
77 
78 	len = ret = 0;
79 	do {
80 		ret = read(p[0], buf + len, sizeof(buf) - 1 - len);
81 		if (ret == -1 && errno == EINTR)
82 			continue;
83 		if (ret <= 0)
84 			break;
85 		len += ret;
86 	} while (sizeof(buf) - 1 - len > 0);
87 	buf[len] = '\0';
88 
89 	close(p[0]);
90 	while (waitpid(pid, &status, 0) < 0)
91 		if (errno != EINTR)
92 			break;
93 
94 	if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
95 		memset(buf, 0, sizeof(buf));
96 		return NULL;
97 	}
98 
99 	buf[strcspn(buf, "\r\n")] = '\0';
100 	pass = xstrdup(buf);
101 	memset(buf, 0, sizeof(buf));
102 	return pass;
103 }
104 
105 /*
106  * Reads a passphrase from /dev/tty with echo turned off/on.  Returns the
107  * passphrase (allocated with xmalloc).  Exits if EOF is encountered. If
108  * RP_ALLOW_STDIN is set, the passphrase will be read from stdin if no
109  * tty is available
110  */
111 char *
112 read_passphrase(const char *prompt, int flags)
113 {
114 	char *askpass = NULL, *ret, buf[1024];
115 	int rppflags, use_askpass = 0, ttyfd;
116 
117 	rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF;
118 	if (flags & RP_USE_ASKPASS)
119 		use_askpass = 1;
120 	else if (flags & RP_ALLOW_STDIN) {
121 		if (!isatty(STDIN_FILENO)) {
122 			debug("read_passphrase: stdin is not a tty");
123 			use_askpass = 1;
124 		}
125 	} else {
126 		rppflags |= RPP_REQUIRE_TTY;
127 		ttyfd = open(_PATH_TTY, O_RDWR);
128 		if (ttyfd >= 0)
129 			close(ttyfd);
130 		else {
131 			debug("read_passphrase: can't open %s: %s", _PATH_TTY,
132 			    strerror(errno));
133 			use_askpass = 1;
134 		}
135 	}
136 
137 	if ((flags & RP_USE_ASKPASS) && getenv("DISPLAY") == NULL)
138 		return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");
139 
140 	if (use_askpass && getenv("DISPLAY")) {
141 		if (getenv(SSH_ASKPASS_ENV))
142 			askpass = getenv(SSH_ASKPASS_ENV);
143 		else
144 			askpass = _PATH_SSH_ASKPASS_DEFAULT;
145 		if ((ret = ssh_askpass(askpass, prompt)) == NULL)
146 			if (!(flags & RP_ALLOW_EOF))
147 				return xstrdup("");
148 		return ret;
149 	}
150 
151 	if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) {
152 		if (flags & RP_ALLOW_EOF)
153 			return NULL;
154 		return xstrdup("");
155 	}
156 
157 	ret = xstrdup(buf);
158 	memset(buf, 'x', sizeof buf);
159 	return ret;
160 }
161 
162 int
163 ask_permission(const char *fmt, ...)
164 {
165 	va_list args;
166 	char *p, prompt[1024];
167 	int allowed = 0;
168 
169 	va_start(args, fmt);
170 	vsnprintf(prompt, sizeof(prompt), fmt, args);
171 	va_end(args);
172 
173 	p = read_passphrase(prompt, RP_USE_ASKPASS|RP_ALLOW_EOF);
174 	if (p != NULL) {
175 		/*
176 		 * Accept empty responses and responses consisting
177 		 * of the word "yes" as affirmative.
178 		 */
179 		if (*p == '\0' || *p == '\n' ||
180 		    strcasecmp(p, "yes") == 0)
181 			allowed = 1;
182 		xfree(p);
183 	}
184 
185 	return (allowed);
186 }
187