1 /* $OpenBSD: readpass.c,v 1.53 2019/01/19 04:15:56 tb 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 <sys/types.h> 27 #include <sys/wait.h> 28 29 #include <errno.h> 30 #include <fcntl.h> 31 #include <paths.h> 32 #include <readpassphrase.h> 33 #include <signal.h> 34 #include <stdarg.h> 35 #include <stdio.h> 36 #include <stdlib.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, ret; 51 size_t len; 52 char *pass; 53 int p[2], status; 54 char buf[1024]; 55 void (*osigchld)(int); 56 57 if (fflush(stdout) != 0) 58 error("ssh_askpass: fflush: %s", strerror(errno)); 59 if (askpass == NULL) 60 fatal("internal error: askpass undefined"); 61 if (pipe(p) < 0) { 62 error("ssh_askpass: pipe: %s", strerror(errno)); 63 return NULL; 64 } 65 osigchld = signal(SIGCHLD, SIG_DFL); 66 if ((pid = fork()) < 0) { 67 error("ssh_askpass: fork: %s", strerror(errno)); 68 signal(SIGCHLD, osigchld); 69 return NULL; 70 } 71 if (pid == 0) { 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 *)NULL); 76 fatal("ssh_askpass: exec(%s): %s", askpass, strerror(errno)); 77 } 78 close(p[1]); 79 80 len = 0; 81 do { 82 ssize_t r = read(p[0], buf + len, sizeof(buf) - 1 - len); 83 84 if (r == -1 && errno == EINTR) 85 continue; 86 if (r <= 0) 87 break; 88 len += r; 89 } while (sizeof(buf) - 1 - len > 0); 90 buf[len] = '\0'; 91 92 close(p[0]); 93 while ((ret = waitpid(pid, &status, 0)) < 0) 94 if (errno != EINTR) 95 break; 96 signal(SIGCHLD, osigchld); 97 if (ret == -1 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) { 98 explicit_bzero(buf, sizeof(buf)); 99 return NULL; 100 } 101 102 buf[strcspn(buf, "\r\n")] = '\0'; 103 pass = xstrdup(buf); 104 explicit_bzero(buf, sizeof(buf)); 105 return pass; 106 } 107 108 /* 109 * Reads a passphrase from /dev/tty with echo turned off/on. Returns the 110 * passphrase (allocated with xmalloc). Exits if EOF is encountered. If 111 * RP_ALLOW_STDIN is set, the passphrase will be read from stdin if no 112 * tty is available 113 */ 114 char * 115 read_passphrase(const char *prompt, int flags) 116 { 117 char cr = '\r', *askpass = NULL, *ret, buf[1024]; 118 int rppflags, use_askpass = 0, ttyfd; 119 120 rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF; 121 if (flags & RP_USE_ASKPASS) 122 use_askpass = 1; 123 else if (flags & RP_ALLOW_STDIN) { 124 if (!isatty(STDIN_FILENO)) { 125 debug("read_passphrase: stdin is not a tty"); 126 use_askpass = 1; 127 } 128 } else { 129 rppflags |= RPP_REQUIRE_TTY; 130 ttyfd = open(_PATH_TTY, O_RDWR); 131 if (ttyfd >= 0) { 132 /* 133 * If we're on a tty, ensure that show the prompt at 134 * the beginning of the line. This will hopefully 135 * clobber any password characters the user has 136 * optimistically typed before echo is disabled. 137 */ 138 (void)write(ttyfd, &cr, 1); 139 close(ttyfd); 140 } else { 141 debug("read_passphrase: can't open %s: %s", _PATH_TTY, 142 strerror(errno)); 143 use_askpass = 1; 144 } 145 } 146 147 if ((flags & RP_USE_ASKPASS) && getenv("DISPLAY") == NULL) 148 return (flags & RP_ALLOW_EOF) ? NULL : xstrdup(""); 149 150 if (use_askpass && getenv("DISPLAY")) { 151 if (getenv(SSH_ASKPASS_ENV)) 152 askpass = getenv(SSH_ASKPASS_ENV); 153 else 154 askpass = _PATH_SSH_ASKPASS_DEFAULT; 155 if ((ret = ssh_askpass(askpass, prompt)) == NULL) 156 if (!(flags & RP_ALLOW_EOF)) 157 return xstrdup(""); 158 return ret; 159 } 160 161 if (readpassphrase(prompt, buf, sizeof buf, rppflags) == NULL) { 162 if (flags & RP_ALLOW_EOF) 163 return NULL; 164 return xstrdup(""); 165 } 166 167 ret = xstrdup(buf); 168 explicit_bzero(buf, sizeof(buf)); 169 return ret; 170 } 171 172 int 173 ask_permission(const char *fmt, ...) 174 { 175 va_list args; 176 char *p, prompt[1024]; 177 int allowed = 0; 178 179 va_start(args, fmt); 180 vsnprintf(prompt, sizeof(prompt), fmt, args); 181 va_end(args); 182 183 p = read_passphrase(prompt, RP_USE_ASKPASS|RP_ALLOW_EOF); 184 if (p != NULL) { 185 /* 186 * Accept empty responses and responses consisting 187 * of the word "yes" as affirmative. 188 */ 189 if (*p == '\0' || *p == '\n' || 190 strcasecmp(p, "yes") == 0) 191 allowed = 1; 192 free(p); 193 } 194 195 return (allowed); 196 } 197