xref: /openssh-portable/readpass.c (revision e7a1e5cf)
1 /* $OpenBSD: readpass.c,v 1.45 2006/07/26 13:57:17 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 <stdlib.h>
38 #include <string.h>
39 #include <unistd.h>
40 
41 #include "xmalloc.h"
42 #include "misc.h"
43 #include "pathnames.h"
44 #include "log.h"
45 #include "ssh.h"
46 #include "uidswap.h"
47 
48 static char *
49 ssh_askpass(char *askpass, const char *msg)
50 {
51 	pid_t pid;
52 	size_t len;
53 	char *pass;
54 	int p[2], status, ret;
55 	char buf[1024];
56 
57 	if (fflush(stdout) != 0)
58 		error("ssh_askpass: fflush: %s", strerror(errno));
59 	if (askpass == NULL)
60 		fatal("internal error: askpass undefined");
61 	if (pipe(p) < 0) {
62 		error("ssh_askpass: pipe: %s", strerror(errno));
63 		return NULL;
64 	}
65 	if ((pid = fork()) < 0) {
66 		error("ssh_askpass: fork: %s", strerror(errno));
67 		return NULL;
68 	}
69 	if (pid == 0) {
70 		permanently_drop_suid(getuid());
71 		close(p[0]);
72 		if (dup2(p[1], STDOUT_FILENO) < 0)
73 			fatal("ssh_askpass: dup2: %s", strerror(errno));
74 		execlp(askpass, askpass, msg, (char *) 0);
75 		fatal("ssh_askpass: exec(%s): %s", askpass, strerror(errno));
76 	}
77 	close(p[1]);
78 
79 	len = ret = 0;
80 	do {
81 		ret = read(p[0], buf + len, sizeof(buf) - 1 - len);
82 		if (ret == -1 && errno == EINTR)
83 			continue;
84 		if (ret <= 0)
85 			break;
86 		len += ret;
87 	} while (sizeof(buf) - 1 - len > 0);
88 	buf[len] = '\0';
89 
90 	close(p[0]);
91 	while (waitpid(pid, &status, 0) < 0)
92 		if (errno != EINTR)
93 			break;
94 
95 	if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
96 		memset(buf, 0, sizeof(buf));
97 		return NULL;
98 	}
99 
100 	buf[strcspn(buf, "\r\n")] = '\0';
101 	pass = xstrdup(buf);
102 	memset(buf, 0, sizeof(buf));
103 	return pass;
104 }
105 
106 /*
107  * Reads a passphrase from /dev/tty with echo turned off/on.  Returns the
108  * passphrase (allocated with xmalloc).  Exits if EOF is encountered. If
109  * RP_ALLOW_STDIN is set, the passphrase will be read from stdin if no
110  * tty is available
111  */
112 char *
113 read_passphrase(const char *prompt, int flags)
114 {
115 	char *askpass = NULL, *ret, buf[1024];
116 	int rppflags, use_askpass = 0, ttyfd;
117 
118 	rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF;
119 	if (flags & RP_USE_ASKPASS)
120 		use_askpass = 1;
121 	else if (flags & RP_ALLOW_STDIN) {
122 		if (!isatty(STDIN_FILENO)) {
123 			debug("read_passphrase: stdin is not a tty");
124 			use_askpass = 1;
125 		}
126 	} else {
127 		rppflags |= RPP_REQUIRE_TTY;
128 		ttyfd = open(_PATH_TTY, O_RDWR);
129 		if (ttyfd >= 0)
130 			close(ttyfd);
131 		else {
132 			debug("read_passphrase: can't open %s: %s", _PATH_TTY,
133 			    strerror(errno));
134 			use_askpass = 1;
135 		}
136 	}
137 
138 	if ((flags & RP_USE_ASKPASS) && getenv("DISPLAY") == NULL)
139 		return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");
140 
141 	if (use_askpass && getenv("DISPLAY")) {
142 		if (getenv(SSH_ASKPASS_ENV))
143 			askpass = getenv(SSH_ASKPASS_ENV);
144 		else
145 			askpass = _PATH_SSH_ASKPASS_DEFAULT;
146 		if ((ret = ssh_askpass(askpass, prompt)) == NULL)
147 			if (!(flags & RP_ALLOW_EOF))
148 				return xstrdup("");
149 		return ret;
150 	}
151 
152 	if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) {
153 		if (flags & RP_ALLOW_EOF)
154 			return NULL;
155 		return xstrdup("");
156 	}
157 
158 	ret = xstrdup(buf);
159 	memset(buf, 'x', sizeof buf);
160 	return ret;
161 }
162 
163 int
164 ask_permission(const char *fmt, ...)
165 {
166 	va_list args;
167 	char *p, prompt[1024];
168 	int allowed = 0;
169 
170 	va_start(args, fmt);
171 	vsnprintf(prompt, sizeof(prompt), fmt, args);
172 	va_end(args);
173 
174 	p = read_passphrase(prompt, RP_USE_ASKPASS|RP_ALLOW_EOF);
175 	if (p != NULL) {
176 		/*
177 		 * Accept empty responses and responses consisting
178 		 * of the word "yes" as affirmative.
179 		 */
180 		if (*p == '\0' || *p == '\n' ||
181 		    strcasecmp(p, "yes") == 0)
182 			allowed = 1;
183 		xfree(p);
184 	}
185 
186 	return (allowed);
187 }
188