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 <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 * 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 * 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) 128 allow_askpass = *s != '\0'; 129 if ((s = getenv(SSH_ASKPASS_REQUIRE_ENV)) != NULL) { 130 if (strcasecmp(s, "force") == 0) { 131 use_askpass = 1; 132 allow_askpass = 1; 133 } else if (strcasecmp(s, "prefer") == 0) 134 use_askpass = allow_askpass; 135 else if (strcasecmp(s, "never") == 0) 136 allow_askpass = 0; 137 } 138 139 rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF; 140 if (use_askpass) 141 debug_f("requested to askpass"); 142 else if (flags & RP_USE_ASKPASS) 143 use_askpass = 1; 144 else if (flags & RP_ALLOW_STDIN) { 145 if (!isatty(STDIN_FILENO)) { 146 debug_f("stdin is not a tty"); 147 use_askpass = 1; 148 } 149 } else { 150 rppflags |= RPP_REQUIRE_TTY; 151 ttyfd = open(_PATH_TTY, O_RDWR); 152 if (ttyfd >= 0) { 153 /* 154 * If we're on a tty, ensure that show the prompt at 155 * the beginning of the line. This will hopefully 156 * clobber any password characters the user has 157 * optimistically typed before echo is disabled. 158 */ 159 (void)write(ttyfd, &cr, 1); 160 close(ttyfd); 161 } else { 162 debug_f("can't open %s: %s", _PATH_TTY, 163 strerror(errno)); 164 use_askpass = 1; 165 } 166 } 167 168 if ((flags & RP_USE_ASKPASS) && !allow_askpass) 169 return (flags & RP_ALLOW_EOF) ? NULL : xstrdup(""); 170 171 if (use_askpass && allow_askpass) { 172 if (getenv(SSH_ASKPASS_ENV)) 173 askpass = getenv(SSH_ASKPASS_ENV); 174 else 175 askpass = _PATH_SSH_ASKPASS_DEFAULT; 176 if ((flags & RP_ASK_PERMISSION) != 0) 177 askpass_hint = "confirm"; 178 if ((ret = ssh_askpass(askpass, prompt, askpass_hint)) == NULL) 179 if (!(flags & RP_ALLOW_EOF)) 180 return xstrdup(""); 181 return ret; 182 } 183 184 if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) { 185 if (flags & RP_ALLOW_EOF) 186 return NULL; 187 return xstrdup(""); 188 } 189 190 ret = xstrdup(buf); 191 explicit_bzero(buf, sizeof(buf)); 192 return ret; 193 } 194 195 int 196 ask_permission(const char *fmt, ...) 197 { 198 va_list args; 199 char *p, prompt[1024]; 200 int allowed = 0; 201 202 va_start(args, fmt); 203 vsnprintf(prompt, sizeof(prompt), fmt, args); 204 va_end(args); 205 206 p = read_passphrase(prompt, 207 RP_USE_ASKPASS|RP_ALLOW_EOF|RP_ASK_PERMISSION); 208 if (p != NULL) { 209 /* 210 * Accept empty responses and responses consisting 211 * of the word "yes" as affirmative. 212 */ 213 if (*p == '\0' || *p == '\n' || 214 strcasecmp(p, "yes") == 0) 215 allowed = 1; 216 free(p); 217 } 218 219 return (allowed); 220 } 221 222 static void 223 writemsg(const char *msg) 224 { 225 (void)write(STDERR_FILENO, "\r", 1); 226 (void)write(STDERR_FILENO, msg, strlen(msg)); 227 (void)write(STDERR_FILENO, "\r\n", 2); 228 } 229 230 struct notifier_ctx { 231 pid_t pid; 232 void (*osigchld)(int); 233 }; 234 235 struct notifier_ctx * 236 notify_start(int force_askpass, const char *fmt, ...) 237 { 238 va_list args; 239 char *prompt = NULL; 240 pid_t pid = -1; 241 void (*osigchld)(int) = NULL; 242 const char *askpass, *s; 243 struct notifier_ctx *ret = NULL; 244 245 va_start(args, fmt); 246 xvasprintf(&prompt, fmt, args); 247 va_end(args); 248 249 if (fflush(NULL) != 0) 250 error_f("fflush: %s", strerror(errno)); 251 if (!force_askpass && isatty(STDERR_FILENO)) { 252 writemsg(prompt); 253 goto out_ctx; 254 } 255 if ((askpass = getenv("SSH_ASKPASS")) == NULL) 256 askpass = _PATH_SSH_ASKPASS_DEFAULT; 257 if (*askpass == '\0') { 258 debug3_f("cannot notify: no askpass"); 259 goto out; 260 } 261 if (getenv("DISPLAY") == NULL && 262 ((s = getenv(SSH_ASKPASS_REQUIRE_ENV)) == NULL || 263 strcmp(s, "force") != 0)) { 264 debug3_f("cannot notify: no display"); 265 goto out; 266 } 267 osigchld = ssh_signal(SIGCHLD, SIG_DFL); 268 if ((pid = fork()) == -1) { 269 error_f("fork: %s", strerror(errno)); 270 ssh_signal(SIGCHLD, osigchld); 271 free(prompt); 272 return NULL; 273 } 274 if (pid == 0) { 275 if (stdfd_devnull(1, 1, 0) == -1) 276 fatal_f("stdfd_devnull failed"); 277 closefrom(STDERR_FILENO + 1); 278 setenv("SSH_ASKPASS_PROMPT", "none", 1); /* hint to UI */ 279 execlp(askpass, askpass, prompt, (char *)NULL); 280 error_f("exec(%s): %s", askpass, strerror(errno)); 281 _exit(1); 282 /* NOTREACHED */ 283 } 284 out_ctx: 285 if ((ret = calloc(1, sizeof(*ret))) == NULL) { 286 kill(pid, SIGTERM); 287 fatal_f("calloc failed"); 288 } 289 ret->pid = pid; 290 ret->osigchld = osigchld; 291 out: 292 free(prompt); 293 return ret; 294 } 295 296 void 297 notify_complete(struct notifier_ctx *ctx, const char *fmt, ...) 298 { 299 int ret; 300 char *msg = NULL; 301 va_list args; 302 303 if (ctx != NULL && fmt != NULL && ctx->pid == -1) { 304 /* 305 * notify_start wrote to stderr, so send conclusion message 306 * there too 307 */ 308 va_start(args, fmt); 309 xvasprintf(&msg, fmt, args); 310 va_end(args); 311 writemsg(msg); 312 free(msg); 313 } 314 315 if (ctx == NULL || ctx->pid <= 0) { 316 free(ctx); 317 return; 318 } 319 kill(ctx->pid, SIGTERM); 320 while ((ret = waitpid(ctx->pid, NULL, 0)) == -1) { 321 if (errno != EINTR) 322 break; 323 } 324 if (ret == -1) 325 fatal_f("waitpid: %s", strerror(errno)); 326 ssh_signal(SIGCHLD, ctx->osigchld); 327 free(ctx); 328 } 329