1 /* $OpenBSD: readpass.c,v 1.69 2021/07/23 05:56:47 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 * 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 * 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 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 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 * 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 kill(pid, SIGTERM); 290 fatal_f("calloc failed"); 291 } 292 ret->pid = pid; 293 ret->osigchld = osigchld; 294 out: 295 free(prompt); 296 return ret; 297 } 298 299 void 300 notify_complete(struct notifier_ctx *ctx, const char *fmt, ...) 301 { 302 int ret; 303 char *msg = NULL; 304 va_list args; 305 306 if (ctx != NULL && fmt != NULL && ctx->pid == -1) { 307 /* 308 * notify_start wrote to stderr, so send conclusion message 309 * there too 310 */ 311 va_start(args, fmt); 312 xvasprintf(&msg, fmt, args); 313 va_end(args); 314 writemsg(msg); 315 free(msg); 316 } 317 318 if (ctx == NULL || ctx->pid <= 0) { 319 free(ctx); 320 return; 321 } 322 kill(ctx->pid, SIGTERM); 323 while ((ret = waitpid(ctx->pid, NULL, 0)) == -1) { 324 if (errno != EINTR) 325 break; 326 } 327 if (ret == -1) 328 fatal_f("waitpid: %s", strerror(errno)); 329 ssh_signal(SIGCHLD, ctx->osigchld); 330 free(ctx); 331 } 332