/* $OpenBSD: readpass.c,v 1.70 2022/05/27 04:27:49 dtucker Exp $ */

/*

 * Copyright (c) 2001 Markus Friedl.  All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the above copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

#include "includes.h"

#include <sys/types.h>

#include <sys/wait.h>

#include <errno.h>

#include <fcntl.h>

#ifdef HAVE_PATHS_H

# include <paths.h>

#endif

#include <signal.h>

#include <stdarg.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <unistd.h>

#include "xmalloc.h"

#include "misc.h"

#include "pathnames.h"

#include "log.h"

#include "ssh.h"

#include "uidswap.h"

static char *

ssh_askpass(char *askpass, const char *msg, const char *env_hint)

{

  pid_t pid, ret;

  size_t len;

  char *pass;

  int p[2], status;

  char buf[1024];

  void (*osigchld)(int);

  if (fflush(stdout) != 0)

    error_f("fflush: %s", strerror(errno));

  if (askpass == NULL)

    fatal("internal error: askpass undefined");

  if (pipe(p) == -1) {

    error_f("pipe: %s", strerror(errno));

    return NULL;

  }

  osigchld = ssh_signal(SIGCHLD, SIG_DFL);

  if ((pid = fork()) == -1) {

    error_f("fork: %s", strerror(errno));

    ssh_signal(SIGCHLD, osigchld);

    return NULL;

  }

  if (pid == 0) {

    close(p[0]);

    if (dup2(p[1], STDOUT_FILENO) == -1)

      fatal_f("dup2: %s", strerror(errno));

    if (env_hint != NULL)

      setenv("SSH_ASKPASS_PROMPT", env_hint, 1);

    execlp(askpass, askpass, msg, (char *)NULL);

    fatal_f("exec(%s): %s", askpass, strerror(errno));

  }

  close(p[1]);

  len = 0;

  do {

    ssize_t r = read(p[0], buf + len, sizeof(buf) - 1 - len);

    if (r == -1 && errno == EINTR)

      continue;

    if (r <= 0)

      break;

    len += r;

  } while (sizeof(buf) - 1 - len > 0);

  buf[len] = '\0';

  close(p[0]);

  while ((ret = waitpid(pid, &status, 0)) == -1)

    if (errno != EINTR)

      break;

  ssh_signal(SIGCHLD, osigchld);

  if (ret == -1 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {

    explicit_bzero(buf, sizeof(buf));

    return NULL;

  }

  buf[strcspn(buf, "\r\n")] = '\0';

  pass = xstrdup(buf);

  explicit_bzero(buf, sizeof(buf));

  return pass;

}

/* private/internal read_passphrase flags */

#define RP_ASK_PERMISSION 0x8000 /* pass hint to askpass for confirm UI */

/*

 * Reads a passphrase from /dev/tty with echo turned off/on.  Returns the

 * passphrase (allocated with xmalloc).  Exits if EOF is encountered. If

 * RP_ALLOW_STDIN is set, the passphrase will be read from stdin if no

 * tty is or askpass program is available

 */

char *

read_passphrase(const char *prompt, int flags)

{

  char cr = '\r', *askpass = NULL, *ret, buf[1024];

  int rppflags, ttyfd, use_askpass = 0, allow_askpass = 0;

  const char *askpass_hint = NULL;

  const char *s;

  if ((s = getenv("DISPLAY")) != NULL)

    allow_askpass = *s != '\0';

  if ((s = getenv(SSH_ASKPASS_REQUIRE_ENV)) != NULL) {

    if (strcasecmp(s, "force") == 0) {

      use_askpass = 1;

      allow_askpass = 1;

    } else if (strcasecmp(s, "prefer") == 0)

      use_askpass = allow_askpass;

    else if (strcasecmp(s, "never") == 0)

      allow_askpass = 0;

  }

  rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF;

  if (use_askpass)

    debug_f("requested to askpass");

  else if (flags & RP_USE_ASKPASS)

    use_askpass = 1;

  else if (flags & RP_ALLOW_STDIN) {

    if (!isatty(STDIN_FILENO)) {

      debug_f("stdin is not a tty");

      use_askpass = 1;

    }

  } else {

    rppflags |= RPP_REQUIRE_TTY;

    ttyfd = open(_PATH_TTY, O_RDWR);

    if (ttyfd >= 0) {

      /*

       * If we're on a tty, ensure that show the prompt at

       * the beginning of the line. This will hopefully

       * clobber any password characters the user has

       * optimistically typed before echo is disabled.

       */

      (void)write(ttyfd, &cr, 1);

      close(ttyfd);

    } else {

      debug_f("can't open %s: %s", _PATH_TTY,

          strerror(errno));

      use_askpass = 1;

    }

  }

  if ((flags & RP_USE_ASKPASS) && !allow_askpass)

    return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");

  if (use_askpass && allow_askpass) {

    if (getenv(SSH_ASKPASS_ENV))

      askpass = getenv(SSH_ASKPASS_ENV);

    else

      askpass = _PATH_SSH_ASKPASS_DEFAULT;

    if ((flags & RP_ASK_PERMISSION) != 0)

      askpass_hint = "confirm";

    if ((ret = ssh_askpass(askpass, prompt, askpass_hint)) == NULL)

      if (!(flags & RP_ALLOW_EOF))

        return xstrdup("");

    return ret;

  }

  if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) {

    if (flags & RP_ALLOW_EOF)

      return NULL;

    return xstrdup("");

  }

  ret = xstrdup(buf);

  explicit_bzero(buf, sizeof(buf));

  return ret;

}

int

ask_permission(const char *fmt, ...)

{

  va_list args;

  char *p, prompt[1024];

  int allowed = 0;

  va_start(args, fmt);

  vsnprintf(prompt, sizeof(prompt), fmt, args);

  va_end(args);

  p = read_passphrase(prompt,

      RP_USE_ASKPASS|RP_ALLOW_EOF|RP_ASK_PERMISSION);

  if (p != NULL) {

    /*

     * Accept empty responses and responses consisting

     * of the word "yes" as affirmative.

     */

    if (*p == '\0' || *p == '\n' ||

        strcasecmp(p, "yes") == 0)

      allowed = 1;

    free(p);

  }

  return (allowed);

}

static void

writemsg(const char *msg)

{

  (void)write(STDERR_FILENO, "\r", 1);

  (void)write(STDERR_FILENO, msg, strlen(msg));

  (void)write(STDERR_FILENO, "\r\n", 2);

}

struct notifier_ctx {

  pid_t pid;

  void (*osigchld)(int);

};

struct notifier_ctx *

notify_start(int force_askpass, const char *fmt, ...)

{

  va_list args;

  char *prompt = NULL;

  pid_t pid = -1;

  void (*osigchld)(int) = NULL;

  const char *askpass, *s;

  struct notifier_ctx *ret = NULL;

  va_start(args, fmt);

  xvasprintf(&prompt, fmt, args);

  va_end(args);

  if (fflush(NULL) != 0)

    error_f("fflush: %s", strerror(errno));

  if (!force_askpass && isatty(STDERR_FILENO)) {

    writemsg(prompt);

    goto out_ctx;

  }

  if ((askpass = getenv("SSH_ASKPASS")) == NULL)

    askpass = _PATH_SSH_ASKPASS_DEFAULT;

  if (*askpass == '\0') {

    debug3_f("cannot notify: no askpass");

    goto out;

  }

  if (getenv("DISPLAY") == NULL &&

      ((s = getenv(SSH_ASKPASS_REQUIRE_ENV)) == NULL ||

      strcmp(s, "force") != 0)) {

    debug3_f("cannot notify: no display");

    goto out;

  }

  osigchld = ssh_signal(SIGCHLD, SIG_DFL);

  if ((pid = fork()) == -1) {

    error_f("fork: %s", strerror(errno));

    ssh_signal(SIGCHLD, osigchld);

    free(prompt);

    return NULL;

  }

  if (pid == 0) {

    if (stdfd_devnull(1, 1, 0) == -1)

      fatal_f("stdfd_devnull failed");

    closefrom(STDERR_FILENO + 1);

    setenv("SSH_ASKPASS_PROMPT", "none", 1); /* hint to UI */

    execlp(askpass, askpass, prompt, (char *)NULL);

    error_f("exec(%s): %s", askpass, strerror(errno));

    _exit(1);

    /* NOTREACHED */

  }

 out_ctx:

  if ((ret = calloc(1, sizeof(*ret))) == NULL) {

    if (pid != -1)

      kill(pid, SIGTERM);

    fatal_f("calloc failed");

  }

  ret->pid = pid;

  ret->osigchld = osigchld;

 out:

  free(prompt);

  return ret;

}

void

notify_complete(struct notifier_ctx *ctx, const char *fmt, ...)

{

  int ret;

  char *msg = NULL;

  va_list args;

  if (ctx != NULL && fmt != NULL && ctx->pid == -1) {

    /*

     * notify_start wrote to stderr, so send conclusion message

     * there too

    */

    va_start(args, fmt);

    xvasprintf(&msg, fmt, args);

    va_end(args);

    writemsg(msg);

    free(msg);

  }

  if (ctx == NULL || ctx->pid <= 0) {

    free(ctx);

    return;

  }

  kill(ctx->pid, SIGTERM);

  while ((ret = waitpid(ctx->pid, NULL, 0)) == -1) {

    if (errno != EINTR)

      break;

  }

  if (ret == -1)

    fatal_f("waitpid: %s", strerror(errno));

  ssh_signal(SIGCHLD, ctx->osigchld);

  free(ctx);

}