1 /* pt_chmod - helper program for `grantpt'.
2 Copyright (C) 1998-2021 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19 #include <argp.h>
20 #include <errno.h>
21 #include <error.h>
22 #include <grp.h>
23 #include <libintl.h>
24 #include <locale.h>
25 #include <signal.h>
26 #include <stdio.h>
27 #include <stdlib.h>
28 #include <string.h>
29 #include <sys/stat.h>
30 #include <unistd.h>
31 #ifdef HAVE_LIBCAP
32 # include <sys/capability.h>
33 # include <sys/prctl.h>
34 #endif
35
36 #include "pty-private.h"
37
38 /* Get libc version number. */
39 #include "../version.h"
40
41 #define PACKAGE _libc_intl_domainname
42
43 /* Name and version of program. */
44 static void print_version (FILE *stream, struct argp_state *state);
45 void (*argp_program_version_hook) (FILE *, struct argp_state *) = print_version;
46
47 /* Function to print some extra text in the help message. */
48 static char *more_help (int key, const char *text, void *input);
49
50 /* Data structure to communicate with argp functions. */
51 static struct argp argp =
52 {
53 NULL, NULL, NULL, NULL, NULL, more_help
54 };
55
56
57 /* Print the version information. */
58 static void
print_version(FILE * stream,struct argp_state * state)59 print_version (FILE *stream, struct argp_state *state)
60 {
61 fprintf (stream, "pt_chown %s%s\n", PKGVERSION, VERSION);
62 fprintf (stream, gettext ("\
63 Copyright (C) %s Free Software Foundation, Inc.\n\
64 This is free software; see the source for copying conditions. There is NO\n\
65 warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.\n\
66 "), "2021");
67 }
68
69 static char *
more_help(int key,const char * text,void * input)70 more_help (int key, const char *text, void *input)
71 {
72 char *cp;
73 char *tp;
74
75 switch (key)
76 {
77 case ARGP_KEY_HELP_PRE_DOC:
78 asprintf (&cp, gettext ("\
79 Set the owner, group and access permission of the slave pseudo\
80 terminal corresponding to the master pseudo terminal passed on\
81 file descriptor `%d'. This is the helper program for the\
82 `grantpt' function. It is not intended to be run directly from\
83 the command line.\n"),
84 PTY_FILENO);
85 return cp;
86 case ARGP_KEY_HELP_EXTRA:
87 /* We print some extra information. */
88 if (asprintf (&tp, gettext ("\
89 For bug reporting instructions, please see:\n\
90 %s.\n"), REPORT_BUGS_TO) < 0)
91 return NULL;
92 if (asprintf (&cp, gettext ("\
93 The owner is set to the current user, the group is set to `%s',\
94 and the access permission is set to `%o'.\n\n\
95 %s"),
96 TTY_GROUP, S_IRUSR|S_IWUSR|S_IWGRP, tp) < 0)
97 {
98 free (tp);
99 return NULL;
100 }
101 return cp;
102 default:
103 break;
104 }
105 return (char *) text;
106 }
107
108 static int
do_pt_chown(void)109 do_pt_chown (void)
110 {
111 char *pty;
112 struct stat64 st;
113 struct group *p;
114 gid_t gid;
115
116 /* Check that PTY_FILENO is a valid master pseudo terminal. */
117 pty = ptsname (PTY_FILENO);
118 if (pty == NULL)
119 return errno == EBADF ? FAIL_EBADF : FAIL_EINVAL;
120
121 /* Check that the returned slave pseudo terminal is a
122 character device. */
123 if (stat64 (pty, &st) < 0 || !S_ISCHR (st.st_mode))
124 return FAIL_EINVAL;
125
126 /* Get the group ID of the special `tty' group. */
127 p = getgrnam (TTY_GROUP);
128 gid = p ? p->gr_gid : getgid ();
129
130 /* Set the owner to the real user ID, and the group to that special
131 group ID. */
132 if (chown (pty, getuid (), gid) < 0)
133 return FAIL_EACCES;
134
135 /* Set the permission mode to readable and writable by the owner,
136 and writable by the group. */
137 if ((st.st_mode & ACCESSPERMS) != (S_IRUSR|S_IWUSR|S_IWGRP)
138 && chmod (pty, S_IRUSR|S_IWUSR|S_IWGRP) < 0)
139 return FAIL_EACCES;
140
141 return 0;
142 }
143
144
145 int
main(int argc,char * argv[])146 main (int argc, char *argv[])
147 {
148 uid_t euid = geteuid ();
149 uid_t uid = getuid ();
150 int remaining;
151 sigset_t signalset;
152
153 /* Clear any signal mask from the parent process. */
154 sigemptyset (&signalset);
155 sigprocmask (SIG_SETMASK, &signalset, NULL);
156
157 if (argc == 1 && euid == 0)
158 {
159 #ifdef HAVE_LIBCAP
160 /* Drop privileges. */
161 if (uid != euid)
162 {
163 static const cap_value_t cap_list[] =
164 { CAP_CHOWN, CAP_FOWNER };
165 # define ncap_list (sizeof (cap_list) / sizeof (cap_list[0]))
166 cap_t caps = cap_init ();
167 if (caps == NULL)
168 return FAIL_ENOMEM;
169
170 /* There is no reason why these should not work. */
171 cap_set_flag (caps, CAP_PERMITTED, ncap_list, cap_list, CAP_SET);
172 cap_set_flag (caps, CAP_EFFECTIVE, ncap_list, cap_list, CAP_SET);
173
174 int res = cap_set_proc (caps);
175
176 cap_free (caps);
177
178 if (__glibc_unlikely (res != 0))
179 return FAIL_EXEC;
180 }
181 #endif
182
183 /* Normal invocation of this program is with no arguments and
184 with privileges. */
185 return do_pt_chown ();
186 }
187
188 /* We aren't going to be using privileges, so drop them right now. */
189 setuid (uid);
190
191 /* Set locale via LC_ALL. */
192 setlocale (LC_ALL, "");
193
194 /* Set the text message domain. */
195 textdomain (PACKAGE);
196
197 /* parse and process arguments. */
198 argp_parse (&argp, argc, argv, 0, &remaining, NULL);
199
200 if (remaining < argc)
201 {
202 /* We should not be called with any non-option parameters. */
203 error (0, 0, gettext ("too many arguments"));
204 argp_help (&argp, stdout, ARGP_HELP_SEE | ARGP_HELP_EXIT_ERR,
205 program_invocation_short_name);
206 return EXIT_FAILURE;
207 }
208
209 /* Check if we are properly installed. */
210 if (euid != 0)
211 error (FAIL_EXEC, 0, gettext ("needs to be installed setuid `root'"));
212
213 return EXIT_SUCCESS;
214 }
215