1 /* $OpenBSD: readpass.c,v 1.61 2020/01/23 07:10:22 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("%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 *
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, use_askpass = 0, ttyfd;
127 const char *askpass_hint = NULL;
128
129 rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF;
130 if (flags & RP_USE_ASKPASS)
131 use_askpass = 1;
132 else if (flags & RP_ALLOW_STDIN) {
133 if (!isatty(STDIN_FILENO)) {
134 debug("read_passphrase: stdin is not a tty");
135 use_askpass = 1;
136 }
137 } else {
138 rppflags |= RPP_REQUIRE_TTY;
139 ttyfd = open(_PATH_TTY, O_RDWR);
140 if (ttyfd >= 0) {
141 /*
142 * If we're on a tty, ensure that show the prompt at
143 * the beginning of the line. This will hopefully
144 * clobber any password characters the user has
145 * optimistically typed before echo is disabled.
146 */
147 (void)write(ttyfd, &cr, 1);
148 close(ttyfd);
149 } else {
150 debug("read_passphrase: can't open %s: %s", _PATH_TTY,
151 strerror(errno));
152 use_askpass = 1;
153 }
154 }
155
156 if ((flags & RP_USE_ASKPASS) && getenv("DISPLAY") == NULL)
157 return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");
158
159 if (use_askpass && getenv("DISPLAY")) {
160 if (getenv(SSH_ASKPASS_ENV))
161 askpass = getenv(SSH_ASKPASS_ENV);
162 else
163 askpass = _PATH_SSH_ASKPASS_DEFAULT;
164 if ((flags & RP_ASK_PERMISSION) != 0)
165 askpass_hint = "confirm";
166 if ((ret = ssh_askpass(askpass, prompt, askpass_hint)) == NULL)
167 if (!(flags & RP_ALLOW_EOF))
168 return xstrdup("");
169 return ret;
170 }
171
172 if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) {
173 if (flags & RP_ALLOW_EOF)
174 return NULL;
175 return xstrdup("");
176 }
177
178 ret = xstrdup(buf);
179 explicit_bzero(buf, sizeof(buf));
180 return ret;
181 }
182
183 int
ask_permission(const char * fmt,...)184 ask_permission(const char *fmt, ...)
185 {
186 va_list args;
187 char *p, prompt[1024];
188 int allowed = 0;
189
190 va_start(args, fmt);
191 vsnprintf(prompt, sizeof(prompt), fmt, args);
192 va_end(args);
193
194 p = read_passphrase(prompt,
195 RP_USE_ASKPASS|RP_ALLOW_EOF|RP_ASK_PERMISSION);
196 if (p != NULL) {
197 /*
198 * Accept empty responses and responses consisting
199 * of the word "yes" as affirmative.
200 */
201 if (*p == '\0' || *p == '\n' ||
202 strcasecmp(p, "yes") == 0)
203 allowed = 1;
204 free(p);
205 }
206
207 return (allowed);
208 }
209
210 struct notifier_ctx {
211 pid_t pid;
212 void (*osigchld)(int);
213 };
214
215 struct notifier_ctx *
notify_start(int force_askpass,const char * fmt,...)216 notify_start(int force_askpass, const char *fmt, ...)
217 {
218 va_list args;
219 char *prompt = NULL;
220 int devnull;
221 pid_t pid;
222 void (*osigchld)(int);
223 const char *askpass;
224 struct notifier_ctx *ret;
225
226 va_start(args, fmt);
227 xvasprintf(&prompt, fmt, args);
228 va_end(args);
229
230 if (fflush(NULL) != 0)
231 error("%s: fflush: %s", __func__, strerror(errno));
232 if (!force_askpass && isatty(STDERR_FILENO)) {
233 (void)write(STDERR_FILENO, "\r", 1);
234 (void)write(STDERR_FILENO, prompt, strlen(prompt));
235 (void)write(STDERR_FILENO, "\r\n", 2);
236 free(prompt);
237 return NULL;
238 }
239 if ((askpass = getenv("SSH_ASKPASS")) == NULL)
240 askpass = _PATH_SSH_ASKPASS_DEFAULT;
241 if (getenv("DISPLAY") == NULL || *askpass == '\0') {
242 debug3("%s: cannot notify", __func__);
243 free(prompt);
244 return NULL;
245 }
246 osigchld = ssh_signal(SIGCHLD, SIG_DFL);
247 if ((pid = fork()) == -1) {
248 error("%s: fork: %s", __func__, strerror(errno));
249 ssh_signal(SIGCHLD, osigchld);
250 free(prompt);
251 return NULL;
252 }
253 if (pid == 0) {
254 if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1)
255 fatal("%s: open %s", __func__, strerror(errno));
256 if (dup2(devnull, STDIN_FILENO) == -1 ||
257 dup2(devnull, STDOUT_FILENO) == -1)
258 fatal("%s: dup2: %s", __func__, strerror(errno));
259 closefrom(STDERR_FILENO + 1);
260 setenv("SSH_ASKPASS_PROMPT", "none", 1); /* hint to UI */
261 execlp(askpass, askpass, prompt, (char *)NULL);
262 error("%s: exec(%s): %s", __func__, askpass, strerror(errno));
263 _exit(1);
264 /* NOTREACHED */
265 }
266 if ((ret = calloc(1, sizeof(*ret))) == NULL) {
267 kill(pid, SIGTERM);
268 fatal("%s: calloc failed", __func__);
269 }
270 ret->pid = pid;
271 ret->osigchld = osigchld;
272 free(prompt);
273 return ret;
274 }
275
276 void
notify_complete(struct notifier_ctx * ctx)277 notify_complete(struct notifier_ctx *ctx)
278 {
279 int ret;
280
281 if (ctx == NULL || ctx->pid <= 0) {
282 free(ctx);
283 return;
284 }
285 kill(ctx->pid, SIGTERM);
286 while ((ret = waitpid(ctx->pid, NULL, 0)) == -1) {
287 if (errno != EINTR)
288 break;
289 }
290 if (ret == -1)
291 fatal("%s: waitpid: %s", __func__, strerror(errno));
292 ssh_signal(SIGCHLD, ctx->osigchld);
293 free(ctx);
294 }
295