xref: /openssh-portable/readpass.c (revision a7a73ee3)
1 /* $OpenBSD: readpass.c,v 1.46 2006/08/01 23:22:47 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 <stdio.h>
38 #include <stdlib.h>
39 #include <string.h>
40 #include <unistd.h>
41 
42 #include "xmalloc.h"
43 #include "misc.h"
44 #include "pathnames.h"
45 #include "log.h"
46 #include "ssh.h"
47 #include "uidswap.h"
48 
49 static char *
50 ssh_askpass(char *askpass, const char *msg)
51 {
52 	pid_t pid;
53 	size_t len;
54 	char *pass;
55 	int p[2], status, ret;
56 	char buf[1024];
57 
58 	if (fflush(stdout) != 0)
59 		error("ssh_askpass: fflush: %s", strerror(errno));
60 	if (askpass == NULL)
61 		fatal("internal error: askpass undefined");
62 	if (pipe(p) < 0) {
63 		error("ssh_askpass: pipe: %s", strerror(errno));
64 		return NULL;
65 	}
66 	if ((pid = fork()) < 0) {
67 		error("ssh_askpass: fork: %s", strerror(errno));
68 		return NULL;
69 	}
70 	if (pid == 0) {
71 		permanently_drop_suid(getuid());
72 		close(p[0]);
73 		if (dup2(p[1], STDOUT_FILENO) < 0)
74 			fatal("ssh_askpass: dup2: %s", strerror(errno));
75 		execlp(askpass, askpass, msg, (char *) 0);
76 		fatal("ssh_askpass: exec(%s): %s", askpass, strerror(errno));
77 	}
78 	close(p[1]);
79 
80 	len = ret = 0;
81 	do {
82 		ret = read(p[0], buf + len, sizeof(buf) - 1 - len);
83 		if (ret == -1 && errno == EINTR)
84 			continue;
85 		if (ret <= 0)
86 			break;
87 		len += ret;
88 	} while (sizeof(buf) - 1 - len > 0);
89 	buf[len] = '\0';
90 
91 	close(p[0]);
92 	while (waitpid(pid, &status, 0) < 0)
93 		if (errno != EINTR)
94 			break;
95 
96 	if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
97 		memset(buf, 0, sizeof(buf));
98 		return NULL;
99 	}
100 
101 	buf[strcspn(buf, "\r\n")] = '\0';
102 	pass = xstrdup(buf);
103 	memset(buf, 0, sizeof(buf));
104 	return pass;
105 }
106 
107 /*
108  * Reads a passphrase from /dev/tty with echo turned off/on.  Returns the
109  * passphrase (allocated with xmalloc).  Exits if EOF is encountered. If
110  * RP_ALLOW_STDIN is set, the passphrase will be read from stdin if no
111  * tty is available
112  */
113 char *
114 read_passphrase(const char *prompt, int flags)
115 {
116 	char *askpass = NULL, *ret, buf[1024];
117 	int rppflags, use_askpass = 0, ttyfd;
118 
119 	rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF;
120 	if (flags & RP_USE_ASKPASS)
121 		use_askpass = 1;
122 	else if (flags & RP_ALLOW_STDIN) {
123 		if (!isatty(STDIN_FILENO)) {
124 			debug("read_passphrase: stdin is not a tty");
125 			use_askpass = 1;
126 		}
127 	} else {
128 		rppflags |= RPP_REQUIRE_TTY;
129 		ttyfd = open(_PATH_TTY, O_RDWR);
130 		if (ttyfd >= 0)
131 			close(ttyfd);
132 		else {
133 			debug("read_passphrase: can't open %s: %s", _PATH_TTY,
134 			    strerror(errno));
135 			use_askpass = 1;
136 		}
137 	}
138 
139 	if ((flags & RP_USE_ASKPASS) && getenv("DISPLAY") == NULL)
140 		return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");
141 
142 	if (use_askpass && getenv("DISPLAY")) {
143 		if (getenv(SSH_ASKPASS_ENV))
144 			askpass = getenv(SSH_ASKPASS_ENV);
145 		else
146 			askpass = _PATH_SSH_ASKPASS_DEFAULT;
147 		if ((ret = ssh_askpass(askpass, prompt)) == NULL)
148 			if (!(flags & RP_ALLOW_EOF))
149 				return xstrdup("");
150 		return ret;
151 	}
152 
153 	if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) {
154 		if (flags & RP_ALLOW_EOF)
155 			return NULL;
156 		return xstrdup("");
157 	}
158 
159 	ret = xstrdup(buf);
160 	memset(buf, 'x', sizeof buf);
161 	return ret;
162 }
163 
164 int
165 ask_permission(const char *fmt, ...)
166 {
167 	va_list args;
168 	char *p, prompt[1024];
169 	int allowed = 0;
170 
171 	va_start(args, fmt);
172 	vsnprintf(prompt, sizeof(prompt), fmt, args);
173 	va_end(args);
174 
175 	p = read_passphrase(prompt, RP_USE_ASKPASS|RP_ALLOW_EOF);
176 	if (p != NULL) {
177 		/*
178 		 * Accept empty responses and responses consisting
179 		 * of the word "yes" as affirmative.
180 		 */
181 		if (*p == '\0' || *p == '\n' ||
182 		    strcasecmp(p, "yes") == 0)
183 			allowed = 1;
184 		xfree(p);
185 	}
186 
187 	return (allowed);
188 }
189