readpass.c

   1 /* $OpenBSD: readpass.c,v 1.48 2010/12/15 00:49:27 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 "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)
  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("ssh_askpass: fflush: %s", strerror(errno));
  62         if (askpass == NULL)
  63                 fatal("internal error: askpass undefined");
  64         if (pipe(p) < 0) {
  65                 error("ssh_askpass: pipe: %s", strerror(errno));
  66                 return NULL;
  67         }
  68         osigchld = signal(SIGCHLD, SIG_DFL);
  69         if ((pid = fork()) < 0) {
  70                 error("ssh_askpass: fork: %s", strerror(errno));
  71                 signal(SIGCHLD, osigchld);
  72                 return NULL;
  73         }
  74         if (pid == 0) {
  75                 permanently_drop_suid(getuid());
  76                 close(p[0]);
  77                 if (dup2(p[1], STDOUT_FILENO) < 0)
  78                         fatal("ssh_askpass: dup2: %s", strerror(errno));
  79                 execlp(askpass, askpass, msg, (char *) 0);
  80                 fatal("ssh_askpass: exec(%s): %s", askpass, strerror(errno));
  81         }
  82         close(p[1]);
  83
  84         len = 0;
  85         do {
  86                 ssize_t r = read(p[0], buf + len, sizeof(buf) - 1 - len);
  87
  88                 if (r == -1 && errno == EINTR)
  89                         continue;
  90                 if (r <= 0)
  91                         break;
  92                 len += r;
  93         } while (sizeof(buf) - 1 - len > 0);
  94         buf[len] = '\0';
  95
  96         close(p[0]);
  97         while ((ret = waitpid(pid, &status, 0)) < 0)
  98                 if (errno != EINTR)
  99                         break;
 100         signal(SIGCHLD, osigchld);
 101         if (ret == -1 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 102                 memset(buf, 0, sizeof(buf));
 103                 return NULL;
 104         }
 105
 106         buf[strcspn(buf, "\r\n")] = '\0';
 107         pass = xstrdup(buf);
 108         memset(buf, 0, sizeof(buf));
 109         return pass;
 110 }
 111
 112 /*
 113  * Reads a passphrase from /dev/tty with echo turned off/on.  Returns the
 114  * passphrase (allocated with xmalloc).  Exits if EOF is encountered. If
 115  * RP_ALLOW_STDIN is set, the passphrase will be read from stdin if no
 116  * tty is available
 117  */
 118 char *
 119 read_passphrase(const char *prompt, int flags)
 120 {
 121         char *askpass = NULL, *ret, buf[1024];
 122         int rppflags, use_askpass = 0, ttyfd;
 123
 124         rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF;
 125         if (flags & RP_USE_ASKPASS)
 126                 use_askpass = 1;
 127         else if (flags & RP_ALLOW_STDIN) {
 128                 if (!isatty(STDIN_FILENO)) {
 129                         debug("read_passphrase: stdin is not a tty");
 130                         use_askpass = 1;
 131                 }
 132         } else {
 133                 rppflags |= RPP_REQUIRE_TTY;
 134                 ttyfd = open(_PATH_TTY, O_RDWR);
 135                 if (ttyfd >= 0)
 136                         close(ttyfd);
 137                 else {
 138                         debug("read_passphrase: can't open %s: %s", _PATH_TTY,
 139                             strerror(errno));
 140                         use_askpass = 1;
 141                 }
 142         }
 143
 144         if ((flags & RP_USE_ASKPASS) && getenv("DISPLAY") == NULL)
 145                 return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");
 146
 147         if (use_askpass && getenv("DISPLAY")) {
 148                 if (getenv(SSH_ASKPASS_ENV))
 149                         askpass = getenv(SSH_ASKPASS_ENV);
 150                 else
 151                         askpass = _PATH_SSH_ASKPASS_DEFAULT;
 152                 if ((ret = ssh_askpass(askpass, prompt)) == NULL)
 153                         if (!(flags & RP_ALLOW_EOF))
 154                                 return xstrdup("");
 155                 return ret;
 156         }
 157
 158         if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) {
 159                 if (flags & RP_ALLOW_EOF)
 160                         return NULL;
 161                 return xstrdup("");
 162         }
 163
 164         ret = xstrdup(buf);
 165         memset(buf, 'x', sizeof buf);
 166         return ret;
 167 }
 168
 169 int
 170 ask_permission(const char *fmt, ...)
 171 {
 172         va_list args;
 173         char *p, prompt[1024];
 174         int allowed = 0;
 175
 176         va_start(args, fmt);
 177         vsnprintf(prompt, sizeof(prompt), fmt, args);
 178         va_end(args);
 179
 180         p = read_passphrase(prompt, RP_USE_ASKPASS|RP_ALLOW_EOF);
 181         if (p != NULL) {
 182                 /*
 183                  * Accept empty responses and responses consisting
 184                  * of the word "yes" as affirmative.
 185                  */
 186                 if (*p == '\0' || *p == '\n' ||
 187                     strcasecmp(p, "yes") == 0)
 188                         allowed = 1;
 189                 xfree(p);
 190         }
 191
 192         return (allowed);
 193 }