1 /* $NetBSD: readpass.c,v 1.16 2021/03/05 17:47:16 christos Exp $ */ 2 /* $OpenBSD: readpass.c,v 1.68 2020/11/10 07:46:20 claudio 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 1.16 2021/03/05 17:47:16 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 * 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 available 122 */ 123 char * 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) 132 allow_askpass = *s != '\0'; 133 if ((s = getenv(SSH_ASKPASS_REQUIRE_ENV)) != NULL) { 134 if (strcasecmp(s, "force") == 0) { 135 use_askpass = 1; 136 allow_askpass = 1; 137 } else if (strcasecmp(s, "prefer") == 0) 138 use_askpass = allow_askpass; 139 else if (strcasecmp(s, "never") == 0) 140 allow_askpass = 0; 141 } 142 143 rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF; 144 if (use_askpass) 145 debug_f("requested to askpass"); 146 else if (flags & RP_USE_ASKPASS) 147 use_askpass = 1; 148 else if (flags & RP_ALLOW_STDIN) { 149 if (!isatty(STDIN_FILENO)) { 150 debug("read_passphrase: stdin is not a tty"); 151 use_askpass = 1; 152 } 153 } else { 154 rppflags |= RPP_REQUIRE_TTY; 155 ttyfd = open(_PATH_TTY, O_RDWR); 156 if (ttyfd >= 0) { 157 /* 158 * If we're on a tty, ensure that show the prompt at 159 * the beginning of the line. This will hopefully 160 * clobber any password characters the user has 161 * optimistically typed before echo is disabled. 162 */ 163 (void)write(ttyfd, &cr, 1); 164 close(ttyfd); 165 } else { 166 debug("read_passphrase: can't open %s: %s", _PATH_TTY, 167 strerror(errno)); 168 use_askpass = 1; 169 } 170 } 171 172 if ((flags & RP_USE_ASKPASS) && !allow_askpass) 173 return (flags & RP_ALLOW_EOF) ? NULL : xstrdup(""); 174 175 if (use_askpass && allow_askpass) { 176 if (getenv(SSH_ASKPASS_ENV)) 177 askpass = getenv(SSH_ASKPASS_ENV); 178 else 179 askpass = _PATH_SSH_ASKPASS_DEFAULT; 180 if ((flags & RP_ASK_PERMISSION) != 0) 181 askpass_hint = "confirm"; 182 if ((ret = ssh_askpass(askpass, prompt, askpass_hint)) == NULL) 183 if (!(flags & RP_ALLOW_EOF)) 184 return xstrdup(""); 185 return ret; 186 } 187 188 if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) { 189 if (flags & RP_ALLOW_EOF) 190 return NULL; 191 return xstrdup(""); 192 } 193 194 ret = xstrdup(buf); 195 explicit_bzero(buf, sizeof(buf)); 196 return ret; 197 } 198 199 int 200 ask_permission(const char *fmt, ...) 201 { 202 va_list args; 203 char *p, prompt[1024]; 204 int allowed = 0; 205 206 va_start(args, fmt); 207 vsnprintf(prompt, sizeof(prompt), fmt, args); 208 va_end(args); 209 210 p = read_passphrase(prompt, 211 RP_USE_ASKPASS|RP_ALLOW_EOF|RP_ASK_PERMISSION); 212 if (p != NULL) { 213 /* 214 * Accept empty responses and responses consisting 215 * of the word "yes" as affirmative. 216 */ 217 if (*p == '\0' || *p == '\n' || 218 strcasecmp(p, "yes") == 0) 219 allowed = 1; 220 free(p); 221 } 222 223 return (allowed); 224 } 225 226 static void 227 writemsg(const char *msg) 228 { 229 (void)write(STDERR_FILENO, "\r", 1); 230 (void)write(STDERR_FILENO, msg, strlen(msg)); 231 (void)write(STDERR_FILENO, "\r\n", 2); 232 } 233 234 struct notifier_ctx { 235 pid_t pid; 236 void (*osigchld)(int); 237 }; 238 239 struct notifier_ctx * 240 notify_start(int force_askpass, const char *fmt, ...) 241 { 242 va_list args; 243 char *prompt = NULL; 244 pid_t pid = -1; 245 void (*osigchld)(int) = NULL; 246 const char *askpass, *s; 247 struct notifier_ctx *ret = NULL; 248 249 va_start(args, fmt); 250 xvasprintf(&prompt, fmt, args); 251 va_end(args); 252 253 if (fflush(NULL) != 0) 254 error_f("fflush: %s", strerror(errno)); 255 if (!force_askpass && isatty(STDERR_FILENO)) { 256 writemsg(prompt); 257 goto out_ctx; 258 } 259 if ((askpass = getenv("SSH_ASKPASS")) == NULL) 260 askpass = _PATH_SSH_ASKPASS_DEFAULT; 261 if (*askpass == '\0') { 262 debug3_f("cannot notify: no askpass"); 263 goto out; 264 } 265 if (getenv("DISPLAY") == NULL && 266 ((s = getenv(SSH_ASKPASS_REQUIRE_ENV)) == NULL || 267 strcmp(s, "force") != 0)) { 268 debug3_f("cannot notify: no display"); 269 goto out; 270 } 271 osigchld = ssh_signal(SIGCHLD, SIG_DFL); 272 if ((pid = fork()) == -1) { 273 error_f("fork: %s", strerror(errno)); 274 ssh_signal(SIGCHLD, osigchld); 275 free(prompt); 276 return NULL; 277 } 278 if (pid == 0) { 279 if (stdfd_devnull(1, 1, 0) == -1) 280 fatal_f("stdfd_devnull failed"); 281 closefrom(STDERR_FILENO + 1); 282 setenv("SSH_ASKPASS_PROMPT", "none", 1); /* hint to UI */ 283 execlp(askpass, askpass, prompt, (char *)NULL); 284 error_f("exec(%s): %s", askpass, strerror(errno)); 285 _exit(1); 286 /* NOTREACHED */ 287 } 288 out_ctx: 289 if ((ret = calloc(1, sizeof(*ret))) == NULL) { 290 kill(pid, SIGTERM); 291 fatal_f("calloc failed"); 292 } 293 ret->pid = pid; 294 ret->osigchld = osigchld; 295 out: 296 free(prompt); 297 return ret; 298 } 299 300 void 301 notify_complete(struct notifier_ctx *ctx, const char *fmt, ...) 302 { 303 int ret; 304 char *msg = NULL; 305 va_list args; 306 307 if (ctx != NULL && fmt != NULL && ctx->pid == -1) { 308 /* 309 * notify_start wrote to stderr, so send conclusion message 310 * there too 311 */ 312 va_start(args, fmt); 313 xvasprintf(&msg, fmt, args); 314 va_end(args); 315 writemsg(msg); 316 free(msg); 317 } 318 319 if (ctx == NULL || ctx->pid <= 0) { 320 free(ctx); 321 return; 322 } 323 kill(ctx->pid, SIGTERM); 324 while ((ret = waitpid(ctx->pid, NULL, 0)) == -1) { 325 if (errno != EINTR) 326 break; 327 } 328 if (ret == -1) 329 fatal_f("waitpid: %s", strerror(errno)); 330 ssh_signal(SIGCHLD, ctx->osigchld); 331 free(ctx); 332 } 333