1 /* $NetBSD: readpass.c,v 1.19 2024/07/08 22:33:44 christos Exp $ */
2 /* $OpenBSD: readpass.c,v 1.71 2024/03/30 04:27:44 djm Exp $ */
3
4 /*
5 * Copyright (c) 2001 Markus Friedl. All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28 #include "includes.h"
29 __RCSID("$NetBSD: readpass.c,v 1.19 2024/07/08 22:33:44 christos Exp $");
30 #include <sys/types.h>
31 #include <sys/wait.h>
32
33 #include <errno.h>
34 #include <fcntl.h>
35 #include <paths.h>
36 #include <readpassphrase.h>
37 #include <signal.h>
38 #include <stdarg.h>
39 #include <stdio.h>
40 #include <stdlib.h>
41 #include <string.h>
42 #include <unistd.h>
43
44 #include "xmalloc.h"
45 #include "misc.h"
46 #include "pathnames.h"
47 #include "log.h"
48 #include "ssh.h"
49 #include "uidswap.h"
50
51 static char *
ssh_askpass(const char * askpass,const char * msg,const char * env_hint)52 ssh_askpass(const char *askpass, const char *msg, const char *env_hint)
53 {
54 pid_t pid, ret;
55 size_t len;
56 char *pass;
57 int p[2], status;
58 char buf[1024];
59 void (*osigchld)(int);
60
61 if (fflush(stdout) != 0)
62 error_f("fflush: %s", strerror(errno));
63 if (askpass == NULL)
64 fatal("internal error: askpass undefined");
65 if (pipe(p) == -1) {
66 error_f("pipe: %s", strerror(errno));
67 return NULL;
68 }
69 osigchld = ssh_signal(SIGCHLD, SIG_DFL);
70 if ((pid = fork()) == -1) {
71 error_f("fork: %s", strerror(errno));
72 ssh_signal(SIGCHLD, osigchld);
73 return NULL;
74 }
75 if (pid == 0) {
76 close(p[0]);
77 if (dup2(p[1], STDOUT_FILENO) == -1)
78 fatal_f("dup2: %s", strerror(errno));
79 if (env_hint != NULL)
80 setenv("SSH_ASKPASS_PROMPT", env_hint, 1);
81 execlp(askpass, askpass, msg, (char *)NULL);
82 fatal_f("exec(%s): %s", askpass, strerror(errno));
83 }
84 close(p[1]);
85
86 len = 0;
87 do {
88 ssize_t r = read(p[0], buf + len, sizeof(buf) - 1 - len);
89
90 if (r == -1 && errno == EINTR)
91 continue;
92 if (r <= 0)
93 break;
94 len += r;
95 } while (sizeof(buf) - 1 - len > 0);
96 buf[len] = '\0';
97
98 close(p[0]);
99 while ((ret = waitpid(pid, &status, 0)) == -1)
100 if (errno != EINTR)
101 break;
102 ssh_signal(SIGCHLD, osigchld);
103 if (ret == -1 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
104 explicit_bzero(buf, sizeof(buf));
105 return NULL;
106 }
107
108 buf[strcspn(buf, "\r\n")] = '\0';
109 pass = xstrdup(buf);
110 explicit_bzero(buf, sizeof(buf));
111 return pass;
112 }
113
114 /* private/internal read_passphrase flags */
115 #define RP_ASK_PERMISSION 0x8000 /* pass hint to askpass for confirm UI */
116
117 /*
118 * Reads a passphrase from /dev/tty with echo turned off/on. Returns the
119 * passphrase (allocated with xmalloc). Exits if EOF is encountered. If
120 * RP_ALLOW_STDIN is set, the passphrase will be read from stdin if no
121 * tty is or askpass program is available
122 */
123 char *
read_passphrase(const char * prompt,int flags)124 read_passphrase(const char *prompt, int flags)
125 {
126 char cr = '\r', *ret, buf[1024];
127 int rppflags, ttyfd, use_askpass = 0, allow_askpass = 0;
128 const char *askpass_hint = NULL, *askpass = NULL;
129 const char *s;
130
131 if (((s = getenv("DISPLAY")) != NULL && *s != '\0') ||
132 ((s = getenv("WAYLAND_DISPLAY")) != NULL && *s != '\0'))
133 allow_askpass = 1;
134 if ((s = getenv(SSH_ASKPASS_REQUIRE_ENV)) != NULL) {
135 if (strcasecmp(s, "force") == 0) {
136 use_askpass = 1;
137 allow_askpass = 1;
138 } else if (strcasecmp(s, "prefer") == 0)
139 use_askpass = allow_askpass;
140 else if (strcasecmp(s, "never") == 0)
141 allow_askpass = 0;
142 }
143
144 rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF;
145 if (use_askpass)
146 debug_f("requested to askpass");
147 else if (flags & RP_USE_ASKPASS)
148 use_askpass = 1;
149 else if (flags & RP_ALLOW_STDIN) {
150 if (!isatty(STDIN_FILENO)) {
151 debug_f("stdin is not a tty");
152 use_askpass = 1;
153 }
154 } else {
155 rppflags |= RPP_REQUIRE_TTY;
156 ttyfd = open(_PATH_TTY, O_RDWR);
157 if (ttyfd >= 0) {
158 /*
159 * If we're on a tty, ensure that show the prompt at
160 * the beginning of the line. This will hopefully
161 * clobber any password characters the user has
162 * optimistically typed before echo is disabled.
163 */
164 (void)write(ttyfd, &cr, 1);
165 close(ttyfd);
166 } else {
167 debug_f("can't open %s: %s", _PATH_TTY,
168 strerror(errno));
169 use_askpass = 1;
170 }
171 }
172
173 if ((flags & RP_USE_ASKPASS) && !allow_askpass)
174 return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");
175
176 if (use_askpass && allow_askpass) {
177 if (getenv(SSH_ASKPASS_ENV))
178 askpass = getenv(SSH_ASKPASS_ENV);
179 else
180 askpass = _PATH_SSH_ASKPASS_DEFAULT;
181 if ((flags & RP_ASK_PERMISSION) != 0)
182 askpass_hint = "confirm";
183 if ((ret = ssh_askpass(askpass, prompt, askpass_hint)) == NULL)
184 if (!(flags & RP_ALLOW_EOF))
185 return xstrdup("");
186 return ret;
187 }
188
189 if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) {
190 if (flags & RP_ALLOW_EOF)
191 return NULL;
192 return xstrdup("");
193 }
194
195 ret = xstrdup(buf);
196 explicit_bzero(buf, sizeof(buf));
197 return ret;
198 }
199
200 int
ask_permission(const char * fmt,...)201 ask_permission(const char *fmt, ...)
202 {
203 va_list args;
204 char *p, prompt[1024];
205 int allowed = 0;
206
207 va_start(args, fmt);
208 vsnprintf(prompt, sizeof(prompt), fmt, args);
209 va_end(args);
210
211 p = read_passphrase(prompt,
212 RP_USE_ASKPASS|RP_ALLOW_EOF|RP_ASK_PERMISSION);
213 if (p != NULL) {
214 /*
215 * Accept empty responses and responses consisting
216 * of the word "yes" as affirmative.
217 */
218 if (*p == '\0' || *p == '\n' ||
219 strcasecmp(p, "yes") == 0)
220 allowed = 1;
221 free(p);
222 }
223
224 return (allowed);
225 }
226
227 static void
writemsg(const char * msg)228 writemsg(const char *msg)
229 {
230 (void)write(STDERR_FILENO, "\r", 1);
231 (void)write(STDERR_FILENO, msg, strlen(msg));
232 (void)write(STDERR_FILENO, "\r\n", 2);
233 }
234
235 struct notifier_ctx {
236 pid_t pid;
237 void (*osigchld)(int);
238 };
239
240 struct notifier_ctx *
notify_start(int force_askpass,const char * fmt,...)241 notify_start(int force_askpass, const char *fmt, ...)
242 {
243 va_list args;
244 char *prompt = NULL;
245 pid_t pid = -1;
246 void (*osigchld)(int) = NULL;
247 const char *askpass, *s;
248 struct notifier_ctx *ret = NULL;
249
250 va_start(args, fmt);
251 xvasprintf(&prompt, fmt, args);
252 va_end(args);
253
254 if (fflush(NULL) != 0)
255 error_f("fflush: %s", strerror(errno));
256 if (!force_askpass && isatty(STDERR_FILENO)) {
257 writemsg(prompt);
258 goto out_ctx;
259 }
260 if ((askpass = getenv("SSH_ASKPASS")) == NULL)
261 askpass = _PATH_SSH_ASKPASS_DEFAULT;
262 if (*askpass == '\0') {
263 debug3_f("cannot notify: no askpass");
264 goto out;
265 }
266 if (getenv("DISPLAY") == NULL && getenv("WAYLAND_DISPLAY") == NULL &&
267 ((s = getenv(SSH_ASKPASS_REQUIRE_ENV)) == NULL ||
268 strcmp(s, "force") != 0)) {
269 debug3_f("cannot notify: no display");
270 goto out;
271 }
272 osigchld = ssh_signal(SIGCHLD, SIG_DFL);
273 if ((pid = fork()) == -1) {
274 error_f("fork: %s", strerror(errno));
275 ssh_signal(SIGCHLD, osigchld);
276 free(prompt);
277 return NULL;
278 }
279 if (pid == 0) {
280 if (stdfd_devnull(1, 1, 0) == -1)
281 fatal_f("stdfd_devnull failed");
282 closefrom(STDERR_FILENO + 1);
283 setenv("SSH_ASKPASS_PROMPT", "none", 1); /* hint to UI */
284 execlp(askpass, askpass, prompt, (char *)NULL);
285 error_f("exec(%s): %s", askpass, strerror(errno));
286 _exit(1);
287 /* NOTREACHED */
288 }
289 out_ctx:
290 if ((ret = calloc(1, sizeof(*ret))) == NULL) {
291 if (pid != -1)
292 kill(pid, SIGTERM);
293 fatal_f("calloc failed");
294 }
295 ret->pid = pid;
296 ret->osigchld = osigchld;
297 out:
298 free(prompt);
299 return ret;
300 }
301
302 void
notify_complete(struct notifier_ctx * ctx,const char * fmt,...)303 notify_complete(struct notifier_ctx *ctx, const char *fmt, ...)
304 {
305 int ret;
306 char *msg = NULL;
307 va_list args;
308
309 if (ctx != NULL && fmt != NULL && ctx->pid == -1) {
310 /*
311 * notify_start wrote to stderr, so send conclusion message
312 * there too
313 */
314 va_start(args, fmt);
315 xvasprintf(&msg, fmt, args);
316 va_end(args);
317 writemsg(msg);
318 free(msg);
319 }
320
321 if (ctx == NULL || ctx->pid <= 0) {
322 free(ctx);
323 return;
324 }
325 kill(ctx->pid, SIGTERM);
326 while ((ret = waitpid(ctx->pid, NULL, 0)) == -1) {
327 if (errno != EINTR)
328 break;
329 }
330 if (ret == -1)
331 fatal_f("waitpid: %s", strerror(errno));
332 ssh_signal(SIGCHLD, ctx->osigchld);
333 free(ctx);
334 }
335