1 /* $OpenBSD: readpass.c,v 1.70 2022/05/27 04:27:49 dtucker 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 *
ssh_askpass(char * askpass,const char * msg,const char * env_hint)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_f("fflush: %s", strerror(errno));
62 if (askpass == NULL)
63 fatal("internal error: askpass undefined");
64 if (pipe(p) == -1) {
65 error_f("pipe: %s", strerror(errno));
66 return NULL;
67 }
68 osigchld = ssh_signal(SIGCHLD, SIG_DFL);
69 if ((pid = fork()) == -1) {
70 error_f("fork: %s", 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_f("dup2: %s", strerror(errno));
78 if (env_hint != NULL)
79 setenv("SSH_ASKPASS_PROMPT", env_hint, 1);
80 execlp(askpass, askpass, msg, (char *)NULL);
81 fatal_f("exec(%s): %s", 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 or askpass program is available
121 */
122 char *
read_passphrase(const char * prompt,int flags)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_f("requested to askpass");
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_f("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_f("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
ask_permission(const char * fmt,...)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 static void
writemsg(const char * msg)226 writemsg(const char *msg)
227 {
228 (void)write(STDERR_FILENO, "\r", 1);
229 (void)write(STDERR_FILENO, msg, strlen(msg));
230 (void)write(STDERR_FILENO, "\r\n", 2);
231 }
232
233 struct notifier_ctx {
234 pid_t pid;
235 void (*osigchld)(int);
236 };
237
238 struct notifier_ctx *
notify_start(int force_askpass,const char * fmt,...)239 notify_start(int force_askpass, const char *fmt, ...)
240 {
241 va_list args;
242 char *prompt = NULL;
243 pid_t pid = -1;
244 void (*osigchld)(int) = NULL;
245 const char *askpass, *s;
246 struct notifier_ctx *ret = NULL;
247
248 va_start(args, fmt);
249 xvasprintf(&prompt, fmt, args);
250 va_end(args);
251
252 if (fflush(NULL) != 0)
253 error_f("fflush: %s", strerror(errno));
254 if (!force_askpass && isatty(STDERR_FILENO)) {
255 writemsg(prompt);
256 goto out_ctx;
257 }
258 if ((askpass = getenv("SSH_ASKPASS")) == NULL)
259 askpass = _PATH_SSH_ASKPASS_DEFAULT;
260 if (*askpass == '\0') {
261 debug3_f("cannot notify: no askpass");
262 goto out;
263 }
264 if (getenv("DISPLAY") == NULL &&
265 ((s = getenv(SSH_ASKPASS_REQUIRE_ENV)) == NULL ||
266 strcmp(s, "force") != 0)) {
267 debug3_f("cannot notify: no display");
268 goto out;
269 }
270 osigchld = ssh_signal(SIGCHLD, SIG_DFL);
271 if ((pid = fork()) == -1) {
272 error_f("fork: %s", strerror(errno));
273 ssh_signal(SIGCHLD, osigchld);
274 free(prompt);
275 return NULL;
276 }
277 if (pid == 0) {
278 if (stdfd_devnull(1, 1, 0) == -1)
279 fatal_f("stdfd_devnull failed");
280 closefrom(STDERR_FILENO + 1);
281 setenv("SSH_ASKPASS_PROMPT", "none", 1); /* hint to UI */
282 execlp(askpass, askpass, prompt, (char *)NULL);
283 error_f("exec(%s): %s", askpass, strerror(errno));
284 _exit(1);
285 /* NOTREACHED */
286 }
287 out_ctx:
288 if ((ret = calloc(1, sizeof(*ret))) == NULL) {
289 if (pid != -1)
290 kill(pid, SIGTERM);
291 fatal_f("calloc failed");
292 }
293 ret->pid = pid;
294 ret->osigchld = osigchld;
295 out:
296 free(prompt);
297 return ret;
298 }
299
300 void
notify_complete(struct notifier_ctx * ctx,const char * fmt,...)301 notify_complete(struct notifier_ctx *ctx, const char *fmt, ...)
302 {
303 int ret;
304 char *msg = NULL;
305 va_list args;
306
307 if (ctx != NULL && fmt != NULL && ctx->pid == -1) {
308 /*
309 * notify_start wrote to stderr, so send conclusion message
310 * there too
311 */
312 va_start(args, fmt);
313 xvasprintf(&msg, fmt, args);
314 va_end(args);
315 writemsg(msg);
316 free(msg);
317 }
318
319 if (ctx == NULL || ctx->pid <= 0) {
320 free(ctx);
321 return;
322 }
323 kill(ctx->pid, SIGTERM);
324 while ((ret = waitpid(ctx->pid, NULL, 0)) == -1) {
325 if (errno != EINTR)
326 break;
327 }
328 if (ret == -1)
329 fatal_f("waitpid: %s", strerror(errno));
330 ssh_signal(SIGCHLD, ctx->osigchld);
331 free(ctx);
332 }
333