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 <sys/types.h>
27 #include <sys/wait.h>
28
29 #include <errno.h>
30 #include <fcntl.h>
31 #include <paths.h>
32 #include <readpassphrase.h>
33 #include <signal.h>
34 #include <stdarg.h>
35 #include <stdio.h>
36 #include <stdlib.h>
37 #include <string.h>
38 #include <unistd.h>
39
40 #include "xmalloc.h"
41 #include "misc.h"
42 #include "pathnames.h"
43 #include "log.h"
44 #include "ssh.h"
45 #include "uidswap.h"
46
47 static char *
ssh_askpass(char * askpass,const char * msg,const char * env_hint)48 ssh_askpass(char *askpass, const char *msg, const char *env_hint)
49 {
50 pid_t pid, ret;
51 size_t len;
52 char *pass;
53 int p[2], status;
54 char buf[1024];
55 void (*osigchld)(int);
56
57 if (fflush(stdout) != 0)
58 error_f("fflush: %s", strerror(errno));
59 if (askpass == NULL)
60 fatal("internal error: askpass undefined");
61 if (pipe(p) == -1) {
62 error_f("pipe: %s", strerror(errno));
63 return NULL;
64 }
65 osigchld = ssh_signal(SIGCHLD, SIG_DFL);
66 if ((pid = fork()) == -1) {
67 error_f("fork: %s", strerror(errno));
68 ssh_signal(SIGCHLD, osigchld);
69 return NULL;
70 }
71 if (pid == 0) {
72 close(p[0]);
73 if (dup2(p[1], STDOUT_FILENO) == -1)
74 fatal_f("dup2: %s", strerror(errno));
75 if (env_hint != NULL)
76 setenv("SSH_ASKPASS_PROMPT", env_hint, 1);
77 execlp(askpass, askpass, msg, (char *)NULL);
78 fatal_f("exec(%s): %s", askpass, strerror(errno));
79 }
80 close(p[1]);
81
82 len = 0;
83 do {
84 ssize_t r = read(p[0], buf + len, sizeof(buf) - 1 - len);
85
86 if (r == -1 && errno == EINTR)
87 continue;
88 if (r <= 0)
89 break;
90 len += r;
91 } while (sizeof(buf) - 1 - len > 0);
92 buf[len] = '\0';
93
94 close(p[0]);
95 while ((ret = waitpid(pid, &status, 0)) == -1)
96 if (errno != EINTR)
97 break;
98 ssh_signal(SIGCHLD, osigchld);
99 if (ret == -1 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
100 explicit_bzero(buf, sizeof(buf));
101 return NULL;
102 }
103
104 buf[strcspn(buf, "\r\n")] = '\0';
105 pass = xstrdup(buf);
106 explicit_bzero(buf, sizeof(buf));
107 return pass;
108 }
109
110 /* private/internal read_passphrase flags */
111 #define RP_ASK_PERMISSION 0x8000 /* pass hint to askpass for confirm UI */
112
113 /*
114 * Reads a passphrase from /dev/tty with echo turned off/on. Returns the
115 * passphrase (allocated with xmalloc). Exits if EOF is encountered. If
116 * RP_ALLOW_STDIN is set, the passphrase will be read from stdin if no
117 * tty is or askpass program is available
118 */
119 char *
read_passphrase(const char * prompt,int flags)120 read_passphrase(const char *prompt, int flags)
121 {
122 char cr = '\r', *askpass = NULL, *ret, buf[1024];
123 int rppflags, ttyfd, use_askpass = 0, allow_askpass = 0;
124 const char *askpass_hint = NULL;
125 const char *s;
126
127 if (((s = getenv("DISPLAY")) != NULL && *s != '\0') ||
128 ((s = getenv("WAYLAND_DISPLAY")) != NULL && *s != '\0'))
129 allow_askpass = 1;
130 if ((s = getenv(SSH_ASKPASS_REQUIRE_ENV)) != NULL) {
131 if (strcasecmp(s, "force") == 0) {
132 use_askpass = 1;
133 allow_askpass = 1;
134 } else if (strcasecmp(s, "prefer") == 0)
135 use_askpass = allow_askpass;
136 else if (strcasecmp(s, "never") == 0)
137 allow_askpass = 0;
138 }
139
140 rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF;
141 if (use_askpass)
142 debug_f("requested to askpass");
143 else if (flags & RP_USE_ASKPASS)
144 use_askpass = 1;
145 else if (flags & RP_ALLOW_STDIN) {
146 if (!isatty(STDIN_FILENO)) {
147 debug_f("stdin is not a tty");
148 use_askpass = 1;
149 }
150 } else {
151 rppflags |= RPP_REQUIRE_TTY;
152 ttyfd = open(_PATH_TTY, O_RDWR);
153 if (ttyfd >= 0) {
154 /*
155 * If we're on a tty, ensure that show the prompt at
156 * the beginning of the line. This will hopefully
157 * clobber any password characters the user has
158 * optimistically typed before echo is disabled.
159 */
160 (void)write(ttyfd, &cr, 1);
161 close(ttyfd);
162 } else {
163 debug_f("can't open %s: %s", _PATH_TTY,
164 strerror(errno));
165 use_askpass = 1;
166 }
167 }
168
169 if ((flags & RP_USE_ASKPASS) && !allow_askpass)
170 return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");
171
172 if (use_askpass && allow_askpass) {
173 if (getenv(SSH_ASKPASS_ENV))
174 askpass = getenv(SSH_ASKPASS_ENV);
175 else
176 askpass = _PATH_SSH_ASKPASS_DEFAULT;
177 if ((flags & RP_ASK_PERMISSION) != 0)
178 askpass_hint = "confirm";
179 if ((ret = ssh_askpass(askpass, prompt, askpass_hint)) == NULL)
180 if (!(flags & RP_ALLOW_EOF))
181 return xstrdup("");
182 return ret;
183 }
184
185 if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) {
186 if (flags & RP_ALLOW_EOF)
187 return NULL;
188 return xstrdup("");
189 }
190
191 ret = xstrdup(buf);
192 explicit_bzero(buf, sizeof(buf));
193 return ret;
194 }
195
196 int
ask_permission(const char * fmt,...)197 ask_permission(const char *fmt, ...)
198 {
199 va_list args;
200 char *p, prompt[1024];
201 int allowed = 0;
202
203 va_start(args, fmt);
204 vsnprintf(prompt, sizeof(prompt), fmt, args);
205 va_end(args);
206
207 p = read_passphrase(prompt,
208 RP_USE_ASKPASS|RP_ALLOW_EOF|RP_ASK_PERMISSION);
209 if (p != NULL) {
210 /*
211 * Accept empty responses and responses consisting
212 * of the word "yes" as affirmative.
213 */
214 if (*p == '\0' || *p == '\n' ||
215 strcasecmp(p, "yes") == 0)
216 allowed = 1;
217 free(p);
218 }
219
220 return (allowed);
221 }
222
223 static void
writemsg(const char * msg)224 writemsg(const char *msg)
225 {
226 (void)write(STDERR_FILENO, "\r", 1);
227 (void)write(STDERR_FILENO, msg, strlen(msg));
228 (void)write(STDERR_FILENO, "\r\n", 2);
229 }
230
231 struct notifier_ctx {
232 pid_t pid;
233 void (*osigchld)(int);
234 };
235
236 struct notifier_ctx *
notify_start(int force_askpass,const char * fmt,...)237 notify_start(int force_askpass, const char *fmt, ...)
238 {
239 va_list args;
240 char *prompt = NULL;
241 pid_t pid = -1;
242 void (*osigchld)(int) = NULL;
243 const char *askpass, *s;
244 struct notifier_ctx *ret = NULL;
245
246 va_start(args, fmt);
247 xvasprintf(&prompt, fmt, args);
248 va_end(args);
249
250 if (fflush(NULL) != 0)
251 error_f("fflush: %s", strerror(errno));
252 if (!force_askpass && isatty(STDERR_FILENO)) {
253 writemsg(prompt);
254 goto out_ctx;
255 }
256 if ((askpass = getenv("SSH_ASKPASS")) == NULL)
257 askpass = _PATH_SSH_ASKPASS_DEFAULT;
258 if (*askpass == '\0') {
259 debug3_f("cannot notify: no askpass");
260 goto out;
261 }
262 if (getenv("DISPLAY") == NULL && getenv("WAYLAND_DISPLAY") == NULL &&
263 ((s = getenv(SSH_ASKPASS_REQUIRE_ENV)) == NULL ||
264 strcmp(s, "force") != 0)) {
265 debug3_f("cannot notify: no display");
266 goto out;
267 }
268 osigchld = ssh_signal(SIGCHLD, SIG_DFL);
269 if ((pid = fork()) == -1) {
270 error_f("fork: %s", strerror(errno));
271 ssh_signal(SIGCHLD, osigchld);
272 free(prompt);
273 return NULL;
274 }
275 if (pid == 0) {
276 if (stdfd_devnull(1, 1, 0) == -1)
277 fatal_f("stdfd_devnull failed");
278 closefrom(STDERR_FILENO + 1);
279 setenv("SSH_ASKPASS_PROMPT", "none", 1); /* hint to UI */
280 execlp(askpass, askpass, prompt, (char *)NULL);
281 error_f("exec(%s): %s", askpass, strerror(errno));
282 _exit(1);
283 /* NOTREACHED */
284 }
285 out_ctx:
286 if ((ret = calloc(1, sizeof(*ret))) == NULL) {
287 if (pid != -1)
288 kill(pid, SIGTERM);
289 fatal_f("calloc failed");
290 }
291 ret->pid = pid;
292 ret->osigchld = osigchld;
293 out:
294 free(prompt);
295 return ret;
296 }
297
298 void
notify_complete(struct notifier_ctx * ctx,const char * fmt,...)299 notify_complete(struct notifier_ctx *ctx, const char *fmt, ...)
300 {
301 int ret;
302 char *msg = NULL;
303 va_list args;
304
305 if (ctx != NULL && fmt != NULL && ctx->pid == -1) {
306 /*
307 * notify_start wrote to stderr, so send conclusion message
308 * there too
309 */
310 va_start(args, fmt);
311 xvasprintf(&msg, fmt, args);
312 va_end(args);
313 writemsg(msg);
314 free(msg);
315 }
316
317 if (ctx == NULL || ctx->pid <= 0) {
318 free(ctx);
319 return;
320 }
321 kill(ctx->pid, SIGTERM);
322 while ((ret = waitpid(ctx->pid, NULL, 0)) == -1) {
323 if (errno != EINTR)
324 break;
325 }
326 if (ret == -1)
327 fatal_f("waitpid: %s", strerror(errno));
328 ssh_signal(SIGCHLD, ctx->osigchld);
329 free(ctx);
330 }
331