readpass.c

   1 /* $OpenBSD: readpass.c,v 1.47 2006/08/03 03:34:42 deraadt 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 <stdarg.h>
  37 #include <stdio.h>
  38 #include <stdlib.h>
  39 #include <string.h>
  40 #include <unistd.h>
  41
  42 #include "xmalloc.h"
  43 #include "misc.h"
  44 #include "pathnames.h"
  45 #include "log.h"
  46 #include "ssh.h"
  47 #include "uidswap.h"
  48
  49 static char *
  50 ssh_askpass(char *askpass, const char *msg)
  51 {
  52         pid_t pid;
  53         size_t len;
  54         char *pass;
  55         int p[2], status, ret;
  56         char buf[1024];
  57
  58         if (fflush(stdout) != 0)
  59                 error("ssh_askpass: fflush: %s", strerror(errno));
  60         if (askpass == NULL)
  61                 fatal("internal error: askpass undefined");
  62         if (pipe(p) < 0) {
  63                 error("ssh_askpass: pipe: %s", strerror(errno));
  64                 return NULL;
  65         }
  66         if ((pid = fork()) < 0) {
  67                 error("ssh_askpass: fork: %s", strerror(errno));
  68                 return NULL;
  69         }
  70         if (pid == 0) {
  71                 permanently_drop_suid(getuid());
  72                 close(p[0]);
  73                 if (dup2(p[1], STDOUT_FILENO) < 0)
  74                         fatal("ssh_askpass: dup2: %s", strerror(errno));
  75                 execlp(askpass, askpass, msg, (char *) 0);
  76                 fatal("ssh_askpass: exec(%s): %s", askpass, strerror(errno));
  77         }
  78         close(p[1]);
  79
  80         len = ret = 0;
  81         do {
  82                 ret = read(p[0], buf + len, sizeof(buf) - 1 - len);
  83                 if (ret == -1 && errno == EINTR)
  84                         continue;
  85                 if (ret <= 0)
  86                         break;
  87                 len += ret;
  88         } while (sizeof(buf) - 1 - len > 0);
  89         buf[len] = '\0';
  90
  91         close(p[0]);
  92         while (waitpid(pid, &status, 0) < 0)
  93                 if (errno != EINTR)
  94                         break;
  95
  96         if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
  97                 memset(buf, 0, sizeof(buf));
  98                 return NULL;
  99         }
 100
 101         buf[strcspn(buf, "\r\n")] = '\0';
 102         pass = xstrdup(buf);
 103         memset(buf, 0, sizeof(buf));
 104         return pass;
 105 }
 106
 107 /*
 108  * Reads a passphrase from /dev/tty with echo turned off/on.  Returns the
 109  * passphrase (allocated with xmalloc).  Exits if EOF is encountered. If
 110  * RP_ALLOW_STDIN is set, the passphrase will be read from stdin if no
 111  * tty is available
 112  */
 113 char *
 114 read_passphrase(const char *prompt, int flags)
 115 {
 116         char *askpass = NULL, *ret, buf[1024];
 117         int rppflags, use_askpass = 0, ttyfd;
 118
 119         rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF;
 120         if (flags & RP_USE_ASKPASS)
 121                 use_askpass = 1;
 122         else if (flags & RP_ALLOW_STDIN) {
 123                 if (!isatty(STDIN_FILENO)) {
 124                         debug("read_passphrase: stdin is not a tty");
 125                         use_askpass = 1;
 126                 }
 127         } else {
 128                 rppflags |= RPP_REQUIRE_TTY;
 129                 ttyfd = open(_PATH_TTY, O_RDWR);
 130                 if (ttyfd >= 0)
 131                         close(ttyfd);
 132                 else {
 133                         debug("read_passphrase: can't open %s: %s", _PATH_TTY,
 134                             strerror(errno));
 135                         use_askpass = 1;
 136                 }
 137         }
 138
 139         if ((flags & RP_USE_ASKPASS) && getenv("DISPLAY") == NULL)
 140                 return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");
 141
 142         if (use_askpass && getenv("DISPLAY")) {
 143                 if (getenv(SSH_ASKPASS_ENV))
 144                         askpass = getenv(SSH_ASKPASS_ENV);
 145                 else
 146                         askpass = _PATH_SSH_ASKPASS_DEFAULT;
 147                 if ((ret = ssh_askpass(askpass, prompt)) == NULL)
 148                         if (!(flags & RP_ALLOW_EOF))
 149                                 return xstrdup("");
 150                 return ret;
 151         }
 152
 153         if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) {
 154                 if (flags & RP_ALLOW_EOF)
 155                         return NULL;
 156                 return xstrdup("");
 157         }
 158
 159         ret = xstrdup(buf);
 160         memset(buf, 'x', sizeof buf);
 161         return ret;
 162 }
 163
 164 int
 165 ask_permission(const char *fmt, ...)
 166 {
 167         va_list args;
 168         char *p, prompt[1024];
 169         int allowed = 0;
 170
 171         va_start(args, fmt);
 172         vsnprintf(prompt, sizeof(prompt), fmt, args);
 173         va_end(args);
 174
 175         p = read_passphrase(prompt, RP_USE_ASKPASS|RP_ALLOW_EOF);
 176         if (p != NULL) {
 177                 /*
 178                  * Accept empty responses and responses consisting
 179                  * of the word "yes" as affirmative.
 180                  */
 181                 if (*p == '\0' || *p == '\n' ||
 182                     strcasecmp(p, "yes") == 0)
 183                         allowed = 1;
 184                 xfree(p);
 185         }
 186
 187         return (allowed);
 188 }