readpass.c

   1 /* $OpenBSD: readpass.c,v 1.44 2006/07/22 20:48:23 stevesk 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 <string.h>
  38 #include <unistd.h>
  39
  40 #include "xmalloc.h"
  41 #include "misc.h"
  42 #include "pathnames.h"
  43 #include "log.h"
  44 #include "ssh.h"
  45 #include "uidswap.h"
  46
  47 static char *
  48 ssh_askpass(char *askpass, const char *msg)
  49 {
  50         pid_t pid;
  51         size_t len;
  52         char *pass;
  53         int p[2], status, ret;
  54         char buf[1024];
  55
  56         if (fflush(stdout) != 0)
  57                 error("ssh_askpass: fflush: %s", strerror(errno));
  58         if (askpass == NULL)
  59                 fatal("internal error: askpass undefined");
  60         if (pipe(p) < 0) {
  61                 error("ssh_askpass: pipe: %s", strerror(errno));
  62                 return NULL;
  63         }
  64         if ((pid = fork()) < 0) {
  65                 error("ssh_askpass: fork: %s", strerror(errno));
  66                 return NULL;
  67         }
  68         if (pid == 0) {
  69                 permanently_drop_suid(getuid());
  70                 close(p[0]);
  71                 if (dup2(p[1], STDOUT_FILENO) < 0)
  72                         fatal("ssh_askpass: dup2: %s", strerror(errno));
  73                 execlp(askpass, askpass, msg, (char *) 0);
  74                 fatal("ssh_askpass: exec(%s): %s", askpass, strerror(errno));
  75         }
  76         close(p[1]);
  77
  78         len = ret = 0;
  79         do {
  80                 ret = read(p[0], buf + len, sizeof(buf) - 1 - len);
  81                 if (ret == -1 && errno == EINTR)
  82                         continue;
  83                 if (ret <= 0)
  84                         break;
  85                 len += ret;
  86         } while (sizeof(buf) - 1 - len > 0);
  87         buf[len] = '\0';
  88
  89         close(p[0]);
  90         while (waitpid(pid, &status, 0) < 0)
  91                 if (errno != EINTR)
  92                         break;
  93
  94         if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
  95                 memset(buf, 0, sizeof(buf));
  96                 return NULL;
  97         }
  98
  99         buf[strcspn(buf, "\r\n")] = '\0';
 100         pass = xstrdup(buf);
 101         memset(buf, 0, sizeof(buf));
 102         return pass;
 103 }
 104
 105 /*
 106  * Reads a passphrase from /dev/tty with echo turned off/on.  Returns the
 107  * passphrase (allocated with xmalloc).  Exits if EOF is encountered. If
 108  * RP_ALLOW_STDIN is set, the passphrase will be read from stdin if no
 109  * tty is available
 110  */
 111 char *
 112 read_passphrase(const char *prompt, int flags)
 113 {
 114         char *askpass = NULL, *ret, buf[1024];
 115         int rppflags, use_askpass = 0, ttyfd;
 116
 117         rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF;
 118         if (flags & RP_USE_ASKPASS)
 119                 use_askpass = 1;
 120         else if (flags & RP_ALLOW_STDIN) {
 121                 if (!isatty(STDIN_FILENO)) {
 122                         debug("read_passphrase: stdin is not a tty");
 123                         use_askpass = 1;
 124                 }
 125         } else {
 126                 rppflags |= RPP_REQUIRE_TTY;
 127                 ttyfd = open(_PATH_TTY, O_RDWR);
 128                 if (ttyfd >= 0)
 129                         close(ttyfd);
 130                 else {
 131                         debug("read_passphrase: can't open %s: %s", _PATH_TTY,
 132                             strerror(errno));
 133                         use_askpass = 1;
 134                 }
 135         }
 136
 137         if ((flags & RP_USE_ASKPASS) && getenv("DISPLAY") == NULL)
 138                 return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");
 139
 140         if (use_askpass && getenv("DISPLAY")) {
 141                 if (getenv(SSH_ASKPASS_ENV))
 142                         askpass = getenv(SSH_ASKPASS_ENV);
 143                 else
 144                         askpass = _PATH_SSH_ASKPASS_DEFAULT;
 145                 if ((ret = ssh_askpass(askpass, prompt)) == NULL)
 146                         if (!(flags & RP_ALLOW_EOF))
 147                                 return xstrdup("");
 148                 return ret;
 149         }
 150
 151         if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) {
 152                 if (flags & RP_ALLOW_EOF)
 153                         return NULL;
 154                 return xstrdup("");
 155         }
 156
 157         ret = xstrdup(buf);
 158         memset(buf, 'x', sizeof buf);
 159         return ret;
 160 }
 161
 162 int
 163 ask_permission(const char *fmt, ...)
 164 {
 165         va_list args;
 166         char *p, prompt[1024];
 167         int allowed = 0;
 168
 169         va_start(args, fmt);
 170         vsnprintf(prompt, sizeof(prompt), fmt, args);
 171         va_end(args);
 172
 173         p = read_passphrase(prompt, RP_USE_ASKPASS|RP_ALLOW_EOF);
 174         if (p != NULL) {
 175                 /*
 176                  * Accept empty responses and responses consisting
 177                  * of the word "yes" as affirmative.
 178                  */
 179                 if (*p == '\0' || *p == '\n' ||
 180                     strcasecmp(p, "yes") == 0)
 181                         allowed = 1;
 182                 xfree(p);
 183         }
 184
 185         return (allowed);
 186 }