1 /* chsh.c - Change login shell.
2 *
3 * Copyright 2021 Michael Christensen
4 *
5 * See http://refspecs.linuxfoundation.org/LSB_4.1.0/LSB-Core-generic/LSB-Core-generic/chsh.html
6
7 USE_CHSH(NEWTOY(chsh, ">1R:s:a", TOYFLAG_USR|TOYFLAG_BIN|TOYFLAG_STAYROOT))
8
9 config CHSH
10 bool "chsh"
11 default n
12 help
13 usage: chsh [-s SHELL] [-R CHROOT_DIR] [USER]
14
15 Change user's login shell.
16
17 -s Use SHELL instead of prompting
18 -R Act on CHROOT_DIR instead of host
19
20 Non-root users can only change their own shell to one listed in /etc/shells.
21 */
22
23 #define FOR_chsh
24 #include "toys.h"
25
26 GLOBALS(
27 char *s, *R;
28 )
29
chsh_main()30 void chsh_main()
31 {
32 FILE *file;
33 char *user, *line, *shell, *encrypted;
34 struct passwd *passwd_info;
35 struct spwd *shadow_info;
36
37 // Get uid user information, may be discarded later
38
39 if ((user = *toys.optargs)) {
40 if (strcmp((passwd_info = xgetpwnam(user))->pw_name, user))
41 if (geteuid()) errno = EPERM, error_exit(0);
42 } else user = (passwd_info = xgetpwuid(getuid()))->pw_name;
43
44 // Get a password, encrypt it, wipe it, and check it
45 if (mlock(toybuf, sizeof(toybuf))) perror_exit("mlock");
46 if (!(shadow_info = getspnam(passwd_info->pw_name))) perror_exit("getspnam");
47 if (read_password(toybuf, sizeof(toybuf), "Password: ")) *toybuf = 0;
48 if (!(encrypted = crypt(toybuf, shadow_info->sp_pwdp))) perror_exit("crypt");
49 memset(toybuf, 0, sizeof(toybuf));
50 munlock(toybuf, sizeof(toybuf)); // prevents memset from "optimizing" away.
51 if (strcmp(encrypted, shadow_info->sp_pwdp)) perror_exit("Bad password");
52
53 // Get new shell (either -s or interactive)
54 file = xfopen("/etc/shells", "r");
55 if (toys.optflags) shell = TT.s;
56 else {
57 xprintf("Login shell for %s [%s]:", user, passwd_info->pw_shell);
58 if (!(shell = xgetline(stdin))) xexit();
59 if (!*shell) xexit();
60 }
61
62 // Verify supplied shell in /etc/shells, or get default shell
63 if (*shell) while ((line = xgetline(file)) && strcmp(shell, line)) free(line);
64 else do line = xgetline(file); while (line && *line != '/');
65 if (!line) error_exit("Shell not found in '/etc/shells'");
66
67 // Update /etc/passwd
68 if (!update_password("/etc/passwd", user, line,6)) perror_exit("/etc/passwd");
69 }
70