crypto/openssh/readpass.c

   1 /* $OpenBSD: readpass.c,v 1.70 2022/05/27 04:27:49 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 *
  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                 if (pid != -1)
 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 }