xref: /openssh-portable/readpass.c (revision aaa8b609)
1 /* $OpenBSD: readpass.c,v 1.62 2020/07/14 23:57:01 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, const char *env_hint)
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("%s: fflush: %s", __func__, strerror(errno));
62 	if (askpass == NULL)
63 		fatal("internal error: askpass undefined");
64 	if (pipe(p) == -1) {
65 		error("%s: pipe: %s", __func__, strerror(errno));
66 		return NULL;
67 	}
68 	osigchld = ssh_signal(SIGCHLD, SIG_DFL);
69 	if ((pid = fork()) == -1) {
70 		error("%s: fork: %s", __func__, strerror(errno));
71 		ssh_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("%s: dup2: %s", __func__, strerror(errno));
78 		if (env_hint != NULL)
79 			setenv("SSH_ASKPASS_PROMPT", env_hint, 1);
80 		execlp(askpass, askpass, msg, (char *)NULL);
81 		fatal("%s: exec(%s): %s", __func__, askpass, strerror(errno));
82 	}
83 	close(p[1]);
84 
85 	len = 0;
86 	do {
87 		ssize_t r = read(p[0], buf + len, sizeof(buf) - 1 - len);
88 
89 		if (r == -1 && errno == EINTR)
90 			continue;
91 		if (r <= 0)
92 			break;
93 		len += r;
94 	} while (sizeof(buf) - 1 - len > 0);
95 	buf[len] = '\0';
96 
97 	close(p[0]);
98 	while ((ret = waitpid(pid, &status, 0)) == -1)
99 		if (errno != EINTR)
100 			break;
101 	ssh_signal(SIGCHLD, osigchld);
102 	if (ret == -1 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
103 		explicit_bzero(buf, sizeof(buf));
104 		return NULL;
105 	}
106 
107 	buf[strcspn(buf, "\r\n")] = '\0';
108 	pass = xstrdup(buf);
109 	explicit_bzero(buf, sizeof(buf));
110 	return pass;
111 }
112 
113 /* private/internal read_passphrase flags */
114 #define RP_ASK_PERMISSION	0x8000 /* pass hint to askpass for confirm UI */
115 
116 /*
117  * Reads a passphrase from /dev/tty with echo turned off/on.  Returns the
118  * passphrase (allocated with xmalloc).  Exits if EOF is encountered. If
119  * RP_ALLOW_STDIN is set, the passphrase will be read from stdin if no
120  * tty is available
121  */
122 char *
123 read_passphrase(const char *prompt, int flags)
124 {
125 	char cr = '\r', *askpass = NULL, *ret, buf[1024];
126 	int rppflags, ttyfd, use_askpass = 0, allow_askpass = 0;
127 	const char *askpass_hint = NULL;
128 	const char *s;
129 
130 	if ((s = getenv("DISPLAY")) != NULL)
131 		allow_askpass = *s != '\0';
132 	if ((s = getenv(SSH_ASKPASS_REQUIRE_ENV)) != NULL) {
133 		if (strcasecmp(s, "force") == 0) {
134 			use_askpass = 1;
135 			allow_askpass = 1;
136 		} else if (strcasecmp(s, "prefer") == 0)
137 			use_askpass = allow_askpass;
138 		else if (strcasecmp(s, "never") == 0)
139 			allow_askpass = 0;
140 	}
141 
142 	rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF;
143 	if (use_askpass)
144 		debug("%s: requested to askpass", __func__);
145 	else if (flags & RP_USE_ASKPASS)
146 		use_askpass = 1;
147 	else if (flags & RP_ALLOW_STDIN) {
148 		if (!isatty(STDIN_FILENO)) {
149 			debug("read_passphrase: stdin is not a tty");
150 			use_askpass = 1;
151 		}
152 	} else {
153 		rppflags |= RPP_REQUIRE_TTY;
154 		ttyfd = open(_PATH_TTY, O_RDWR);
155 		if (ttyfd >= 0) {
156 			/*
157 			 * If we're on a tty, ensure that show the prompt at
158 			 * the beginning of the line. This will hopefully
159 			 * clobber any password characters the user has
160 			 * optimistically typed before echo is disabled.
161 			 */
162 			(void)write(ttyfd, &cr, 1);
163 			close(ttyfd);
164 		} else {
165 			debug("read_passphrase: can't open %s: %s", _PATH_TTY,
166 			    strerror(errno));
167 			use_askpass = 1;
168 		}
169 	}
170 
171 	if ((flags & RP_USE_ASKPASS) && !allow_askpass)
172 		return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");
173 
174 	if (use_askpass && allow_askpass) {
175 		if (getenv(SSH_ASKPASS_ENV))
176 			askpass = getenv(SSH_ASKPASS_ENV);
177 		else
178 			askpass = _PATH_SSH_ASKPASS_DEFAULT;
179 		if ((flags & RP_ASK_PERMISSION) != 0)
180 			askpass_hint = "confirm";
181 		if ((ret = ssh_askpass(askpass, prompt, askpass_hint)) == NULL)
182 			if (!(flags & RP_ALLOW_EOF))
183 				return xstrdup("");
184 		return ret;
185 	}
186 
187 	if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) {
188 		if (flags & RP_ALLOW_EOF)
189 			return NULL;
190 		return xstrdup("");
191 	}
192 
193 	ret = xstrdup(buf);
194 	explicit_bzero(buf, sizeof(buf));
195 	return ret;
196 }
197 
198 int
199 ask_permission(const char *fmt, ...)
200 {
201 	va_list args;
202 	char *p, prompt[1024];
203 	int allowed = 0;
204 
205 	va_start(args, fmt);
206 	vsnprintf(prompt, sizeof(prompt), fmt, args);
207 	va_end(args);
208 
209 	p = read_passphrase(prompt,
210 	    RP_USE_ASKPASS|RP_ALLOW_EOF|RP_ASK_PERMISSION);
211 	if (p != NULL) {
212 		/*
213 		 * Accept empty responses and responses consisting
214 		 * of the word "yes" as affirmative.
215 		 */
216 		if (*p == '\0' || *p == '\n' ||
217 		    strcasecmp(p, "yes") == 0)
218 			allowed = 1;
219 		free(p);
220 	}
221 
222 	return (allowed);
223 }
224 
225 struct notifier_ctx {
226 	pid_t pid;
227 	void (*osigchld)(int);
228 };
229 
230 struct notifier_ctx *
231 notify_start(int force_askpass, const char *fmt, ...)
232 {
233 	va_list args;
234 	char *prompt = NULL;
235 	int devnull;
236 	pid_t pid;
237 	void (*osigchld)(int);
238 	const char *askpass;
239 	struct notifier_ctx *ret;
240 
241 	va_start(args, fmt);
242 	xvasprintf(&prompt, fmt, args);
243 	va_end(args);
244 
245 	if (fflush(NULL) != 0)
246 		error("%s: fflush: %s", __func__, strerror(errno));
247 	if (!force_askpass && isatty(STDERR_FILENO)) {
248 		(void)write(STDERR_FILENO, "\r", 1);
249 		(void)write(STDERR_FILENO, prompt, strlen(prompt));
250 		(void)write(STDERR_FILENO, "\r\n", 2);
251 		free(prompt);
252 		return NULL;
253 	}
254 	if ((askpass = getenv("SSH_ASKPASS")) == NULL)
255 		askpass = _PATH_SSH_ASKPASS_DEFAULT;
256 	if (getenv("DISPLAY") == NULL || *askpass == '\0') {
257 		debug3("%s: cannot notify", __func__);
258 		free(prompt);
259 		return NULL;
260 	}
261 	osigchld = ssh_signal(SIGCHLD, SIG_DFL);
262 	if ((pid = fork()) == -1) {
263 		error("%s: fork: %s", __func__, strerror(errno));
264 		ssh_signal(SIGCHLD, osigchld);
265 		free(prompt);
266 		return NULL;
267 	}
268 	if (pid == 0) {
269 		if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1)
270 			fatal("%s: open %s", __func__, strerror(errno));
271 		if (dup2(devnull, STDIN_FILENO) == -1 ||
272 		    dup2(devnull, STDOUT_FILENO) == -1)
273 			fatal("%s: dup2: %s", __func__, strerror(errno));
274 		closefrom(STDERR_FILENO + 1);
275 		setenv("SSH_ASKPASS_PROMPT", "none", 1); /* hint to UI */
276 		execlp(askpass, askpass, prompt, (char *)NULL);
277 		error("%s: exec(%s): %s", __func__, askpass, strerror(errno));
278 		_exit(1);
279 		/* NOTREACHED */
280 	}
281 	if ((ret = calloc(1, sizeof(*ret))) == NULL) {
282 		kill(pid, SIGTERM);
283 		fatal("%s: calloc failed", __func__);
284 	}
285 	ret->pid = pid;
286 	ret->osigchld = osigchld;
287 	free(prompt);
288 	return ret;
289 }
290 
291 void
292 notify_complete(struct notifier_ctx *ctx)
293 {
294 	int ret;
295 
296 	if (ctx == NULL || ctx->pid <= 0) {
297 		free(ctx);
298 		return;
299 	}
300 	kill(ctx->pid, SIGTERM);
301 	while ((ret = waitpid(ctx->pid, NULL, 0)) == -1) {
302 		if (errno != EINTR)
303 			break;
304 	}
305 	if (ret == -1)
306 		fatal("%s: waitpid: %s", __func__, strerror(errno));
307 	ssh_signal(SIGCHLD, ctx->osigchld);
308 	free(ctx);
309 }
310