1 /* $OpenBSD: readpass.c,v 1.71 2024/03/30 04:27:44 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 *
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 && *s != '\0') ||
131 ((s = getenv("WAYLAND_DISPLAY")) != NULL && *s != '\0'))
132 allow_askpass = 1;
133 if ((s = getenv(SSH_ASKPASS_REQUIRE_ENV)) != NULL) {
134 if (strcasecmp(s, "force") == 0) {
135 use_askpass = 1;
136 allow_askpass = 1;
137 } else if (strcasecmp(s, "prefer") == 0)
138 use_askpass = allow_askpass;
139 else if (strcasecmp(s, "never") == 0)
140 allow_askpass = 0;
141 }
142
143 rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF;
144 if (use_askpass)
145 debug_f("requested to askpass");
146 else if (flags & RP_USE_ASKPASS)
147 use_askpass = 1;
148 else if (flags & RP_ALLOW_STDIN) {
149 if (!isatty(STDIN_FILENO)) {
150 debug_f("stdin is not a tty");
151 use_askpass = 1;
152 }
153 } else {
154 rppflags |= RPP_REQUIRE_TTY;
155 ttyfd = open(_PATH_TTY, O_RDWR);
156 if (ttyfd >= 0) {
157 /*
158 * If we're on a tty, ensure that show the prompt at
159 * the beginning of the line. This will hopefully
160 * clobber any password characters the user has
161 * optimistically typed before echo is disabled.
162 */
163 (void)write(ttyfd, &cr, 1);
164 close(ttyfd);
165 } else {
166 debug_f("can't open %s: %s", _PATH_TTY,
167 strerror(errno));
168 use_askpass = 1;
169 }
170 }
171
172 if ((flags & RP_USE_ASKPASS) && !allow_askpass)
173 return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");
174
175 if (use_askpass && allow_askpass) {
176 if (getenv(SSH_ASKPASS_ENV))
177 askpass = getenv(SSH_ASKPASS_ENV);
178 else
179 askpass = _PATH_SSH_ASKPASS_DEFAULT;
180 if ((flags & RP_ASK_PERMISSION) != 0)
181 askpass_hint = "confirm";
182 if ((ret = ssh_askpass(askpass, prompt, askpass_hint)) == NULL)
183 if (!(flags & RP_ALLOW_EOF))
184 return xstrdup("");
185 return ret;
186 }
187
188 if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) {
189 if (flags & RP_ALLOW_EOF)
190 return NULL;
191 return xstrdup("");
192 }
193
194 ret = xstrdup(buf);
195 explicit_bzero(buf, sizeof(buf));
196 return ret;
197 }
198
199 int
ask_permission(const char * fmt,...)200 ask_permission(const char *fmt, ...)
201 {
202 va_list args;
203 char *p, prompt[1024];
204 int allowed = 0;
205
206 va_start(args, fmt);
207 vsnprintf(prompt, sizeof(prompt), fmt, args);
208 va_end(args);
209
210 p = read_passphrase(prompt,
211 RP_USE_ASKPASS|RP_ALLOW_EOF|RP_ASK_PERMISSION);
212 if (p != NULL) {
213 /*
214 * Accept empty responses and responses consisting
215 * of the word "yes" as affirmative.
216 */
217 if (*p == '\0' || *p == '\n' ||
218 strcasecmp(p, "yes") == 0)
219 allowed = 1;
220 free(p);
221 }
222
223 return (allowed);
224 }
225
226 static void
writemsg(const char * msg)227 writemsg(const char *msg)
228 {
229 (void)write(STDERR_FILENO, "\r", 1);
230 (void)write(STDERR_FILENO, msg, strlen(msg));
231 (void)write(STDERR_FILENO, "\r\n", 2);
232 }
233
234 struct notifier_ctx {
235 pid_t pid;
236 void (*osigchld)(int);
237 };
238
239 struct notifier_ctx *
notify_start(int force_askpass,const char * fmt,...)240 notify_start(int force_askpass, const char *fmt, ...)
241 {
242 va_list args;
243 char *prompt = NULL;
244 pid_t pid = -1;
245 void (*osigchld)(int) = NULL;
246 const char *askpass, *s;
247 struct notifier_ctx *ret = NULL;
248
249 va_start(args, fmt);
250 xvasprintf(&prompt, fmt, args);
251 va_end(args);
252
253 if (fflush(NULL) != 0)
254 error_f("fflush: %s", strerror(errno));
255 if (!force_askpass && isatty(STDERR_FILENO)) {
256 writemsg(prompt);
257 goto out_ctx;
258 }
259 if ((askpass = getenv("SSH_ASKPASS")) == NULL)
260 askpass = _PATH_SSH_ASKPASS_DEFAULT;
261 if (*askpass == '\0') {
262 debug3_f("cannot notify: no askpass");
263 goto out;
264 }
265 if (getenv("DISPLAY") == NULL && getenv("WAYLAND_DISPLAY") == NULL &&
266 ((s = getenv(SSH_ASKPASS_REQUIRE_ENV)) == NULL ||
267 strcmp(s, "force") != 0)) {
268 debug3_f("cannot notify: no display");
269 goto out;
270 }
271 osigchld = ssh_signal(SIGCHLD, SIG_DFL);
272 if ((pid = fork()) == -1) {
273 error_f("fork: %s", strerror(errno));
274 ssh_signal(SIGCHLD, osigchld);
275 free(prompt);
276 return NULL;
277 }
278 if (pid == 0) {
279 if (stdfd_devnull(1, 1, 0) == -1)
280 fatal_f("stdfd_devnull failed");
281 closefrom(STDERR_FILENO + 1);
282 setenv("SSH_ASKPASS_PROMPT", "none", 1); /* hint to UI */
283 execlp(askpass, askpass, prompt, (char *)NULL);
284 error_f("exec(%s): %s", askpass, strerror(errno));
285 _exit(1);
286 /* NOTREACHED */
287 }
288 out_ctx:
289 if ((ret = calloc(1, sizeof(*ret))) == NULL) {
290 if (pid != -1)
291 kill(pid, SIGTERM);
292 fatal_f("calloc failed");
293 }
294 ret->pid = pid;
295 ret->osigchld = osigchld;
296 out:
297 free(prompt);
298 return ret;
299 }
300
301 void
notify_complete(struct notifier_ctx * ctx,const char * fmt,...)302 notify_complete(struct notifier_ctx *ctx, const char *fmt, ...)
303 {
304 int ret;
305 char *msg = NULL;
306 va_list args;
307
308 if (ctx != NULL && fmt != NULL && ctx->pid == -1) {
309 /*
310 * notify_start wrote to stderr, so send conclusion message
311 * there too
312 */
313 va_start(args, fmt);
314 xvasprintf(&msg, fmt, args);
315 va_end(args);
316 writemsg(msg);
317 free(msg);
318 }
319
320 if (ctx == NULL || ctx->pid <= 0) {
321 free(ctx);
322 return;
323 }
324 kill(ctx->pid, SIGTERM);
325 while ((ret = waitpid(ctx->pid, NULL, 0)) == -1) {
326 if (errno != EINTR)
327 break;
328 }
329 if (ret == -1)
330 fatal_f("waitpid: %s", strerror(errno));
331 ssh_signal(SIGCHLD, ctx->osigchld);
332 free(ctx);
333 }
334