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Ørjan Malde |
d16cc0 |
/* mlogin: minimalistic login */
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Ørjan Malde |
d16cc0 |
/* Copyright (c) 2019 Ørjan Malde */
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Ørjan Malde |
d16cc0 |
/* Released under LGPL, see COPYRIGHT.MLOGIN */
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Ørjan Malde |
d16cc0 |
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Ørjan Malde |
24d238 |
#define _GNU_SOURCE
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Ørjan Malde |
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#include <sys/types.h>
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Ørjan Malde |
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#include <unistd.h>
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Ørjan Malde |
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#include <stdlib.h>
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Ørjan Malde |
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#include <stdio.h>
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Ørjan Malde |
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#include <stdbool.h>
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Ørjan Malde |
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#include <string.h>
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Ørjan Malde |
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#include <grp.h>
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Ørjan Malde |
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#include <pwd.h>
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Ørjan Malde |
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#include <errno.h>
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Ørjan Malde |
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#include <signal.h>
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Ørjan Malde |
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#ifdef __midipix__
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Ørjan Malde |
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#define IFLAG 1
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Ørjan Malde |
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#else
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Ørjan Malde |
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#define IFLAG 0
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Ørjan Malde |
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#endif
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Ørjan Malde |
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Ørjan Malde |
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#include "login.h"
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Ørjan Malde |
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#ifndef HAVE_EXPLICIT_BZERO
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void explicit_bzero(void*, size_t);
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#endif
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Ørjan Malde |
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Ørjan Malde |
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static bool switch_user_context(struct passwd* pw, const char* username)
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Ørjan Malde |
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{
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#ifndef __midipix__
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if(!getuid()) {
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if(initgroups(username, pw->pw_gid) == -1) {
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printf("initgroups failed: %s", strerror(errno));
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exit(1);
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}
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Ørjan Malde |
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}
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Ørjan Malde |
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#endif
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/* this works for linux and midipix */
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if(setgid(pw->pw_gid))
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return false;
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if(setuid(pw->pw_uid))
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return false;
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return true;
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}
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static bool do_login(struct passwd* pwd, int pflag)
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{
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if(*pwd->pw_shell == '\0')
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pwd->pw_shell = "/bin/sh"; /* if /bin/sh doesn't exist, I do not care. blow up. */
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if(chdir(pwd->pw_dir) < 0) {
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printf("no home directory %s!\n", pwd->pw_dir); // handle -EPERM, -ENOMEM, -ESYMLNK
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if(chdir("/") == -1) {
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printf("chdir failed with %s", strerror(errno));
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return false;
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}
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pwd->pw_dir = "/";
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}
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if(!pflag)
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(void)clearenv();
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(void)setenv("HOME", pwd->pw_dir, 1);
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(void)setenv("SHELL", pwd->pw_shell, 1);
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(void)setenv("TERM", "xterm", 0); /* rrrr. needs researching */
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(void)setenv("LOGNAME", pwd->pw_name, 1);
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(void)setenv("USER", pwd->pw_name, 1);
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#if 0
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(void)setenv("PS1", "$ ", 0);
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#endif
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(void)setenv("PATH", "/local/sbin:/local/bin:/sbin:/bin", 0);
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(void)signal(SIGTSTP, SIG_DFL);
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(void)signal(SIGQUIT, SIG_DFL);
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(void)signal(SIGINT, SIG_DFL);
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execlp(pwd->pw_shell, "-l", (const char*)NULL);
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Ørjan Malde |
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return false;
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Ørjan Malde |
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}
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Ørjan Malde |
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Ørjan Malde |
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int main(int argc, char **argv)
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Ørjan Malde |
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{
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Ørjan Malde |
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/* we don't want ^D etc to mess up the logic */
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Ørjan Malde |
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(void)signal(SIGTSTP, SIG_IGN);
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Ørjan Malde |
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(void)signal(SIGQUIT, SIG_IGN);
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Ørjan Malde |
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(void)signal(SIGINT, SIG_IGN);
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Ørjan Malde |
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Ørjan Malde |
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struct passwd *pwd;
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Ørjan Malde |
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char* username = NULL;
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Ørjan Malde |
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int c;
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int pflag, fflag, iflag = 0;
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Ørjan Malde |
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Ørjan Malde |
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while((c = getopt(argc, argv, "pfh:iw")) != -1)
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Ørjan Malde |
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switch(c) {
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Ørjan Malde |
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case 'p':
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Ørjan Malde |
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pflag = 1; break;
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Ørjan Malde |
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case 'f':
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Ørjan Malde |
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fflag = 1; break; /* unused, pointless currently */
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Ørjan Malde |
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case 'h':
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Ørjan Malde |
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if(getuid()) {
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Ørjan Malde |
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exit(1);
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Ørjan Malde |
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}
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Ørjan Malde |
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break;
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Ørjan Malde |
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case 'i':
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Ørjan Malde |
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iflag = IFLAG; break;
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Ørjan Malde |
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default:
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Ørjan Malde |
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case '?':
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Ørjan Malde |
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usage();
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Ørjan Malde |
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break;
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Ørjan Malde |
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}
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argv += optind;
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Ørjan Malde |
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if(*argv)
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Ørjan Malde |
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username = *argv;
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Ørjan Malde |
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else {
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Ørjan Malde |
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printf("login: ");
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Ørjan Malde |
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fflush(0);
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Ørjan Malde |
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(void)scanf("%ms", &username);
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Ørjan Malde |
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}
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Ørjan Malde |
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pwd = getpwnam(username);
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if(pwd) {
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if(!iflag) {
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char* pw = getpass("Password: ");
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if(!(*pwd->pw_passwd == '\0' && !strlen(pw))) {
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Ørjan Malde |
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char* pw_encrypted = crypt(pw, pwd->pw_passwd);
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if(!timingsafe_memcmp(pw_encrypted, pwd->pw_passwd, strlen(pw_encrypted))) {
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puts("Login incorrect.");
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explicit_bzero(pw, strlen(pw));
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exit(1);
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}
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explicit_bzero(pw, strlen(pw));
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Ørjan Malde |
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}
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Ørjan Malde |
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}
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}
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else {
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/* asking for password even if the user is not found, no /etc/passwd is found, etc. */
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/* this stops easy probing for accounts */
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char* pw = getpass("Password: ");
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puts("Login incorrect.");
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explicit_bzero(pw, strlen(pw));
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exit(1);
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}
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Ørjan Malde |
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endpwent();
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Ørjan Malde |
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Ørjan Malde |
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/* authenticated, attempt to set user context and spawn user shell */
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Ørjan Malde |
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if(switch_user_context(pwd, username)) {
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if(!do_login(pwd, pflag)) {
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puts("failed to spawn shell.");
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Ørjan Malde |
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}
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Ørjan Malde |
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}
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Ørjan Malde |
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puts("could not switch to specified user.");
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Ørjan Malde |
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}
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Ørjan Malde |
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Ørjan Malde |
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void usage(void) {
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Ørjan Malde |
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puts("login -p (preserve environment)");
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Ørjan Malde |
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puts("login -f (no secondary authentication, unused)");
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Ørjan Malde |
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puts("login -h (pass remote server name to login, unused)");
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Ørjan Malde |
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exit(0);
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Ørjan Malde |
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}
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