1 /* $OpenBSD: readpass.c,v 1.51 2015/12/11 00:20:04 mmcc 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 *
ssh_askpass(char * askpass,const char * msg)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 *)NULL);
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 explicit_bzero(buf, sizeof(buf));
103 return NULL;
104 }
105
106 buf[strcspn(buf, "\r\n")] = '\0';
107 pass = xstrdup(buf);
108 explicit_bzero(buf, 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 *
read_passphrase(const char * prompt,int flags)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 explicit_bzero(buf, sizeof(buf));
166 return ret;
167 }
168
169 int
ask_permission(const char * fmt,...)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 free(p);
190 }
191
192 return (allowed);
193 }
194