109 lines
2.2 KiB
C
109 lines
2.2 KiB
C
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#include <errno.h>
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#include <pwd.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/wait.h>
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#include <unistd.h>
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static char* echoing_fgets(char* buf, size_t size, FILE* stream)
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{
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char* s = buf;
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memset(buf, 0, size);
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while (size)
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{
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int c = fgetc(stream);
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if (c == EOF)
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{
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if (ferror(stream)) return NULL;
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if (feof(stream))
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{
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if (s != buf) return s;
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else
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return NULL;
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};
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}
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size--;
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*buf = (char)c;
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buf++;
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*buf = 0;
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putchar((char)c);
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if ((char)c == '\n') return s;
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}
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return s;
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}
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static void strip_newline(char* str)
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{
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size_t len = strlen(str);
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if (str[len - 1] == '\n') str[len - 1] = 0;
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}
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static void login_as(struct passwd* user)
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{
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pid_t child = fork();
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if (child < 0)
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{
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perror("fork");
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return;
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}
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if (child == 0)
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{
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setuid(user->pw_uid);
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setgid(user->pw_gid);
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char* argv[] = {user->pw_shell, NULL};
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execv(argv[0], argv);
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perror("execv");
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exit(EXIT_FAILURE);
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}
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wait(NULL);
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}
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static int login()
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{
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printf("Username: ");
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char username[BUFSIZ];
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echoing_fgets(username, BUFSIZ, stdin);
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strip_newline(username);
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if (strcmp("exit", username) == 0) return 1;
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struct passwd* user = getpwnam(username);
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if (!user)
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{
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if (errno) perror("getpwnam");
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else
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printf("Unknown user %s\n", username);
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return 0;
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}
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printf("Password: ");
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char password[BUFSIZ];
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fgets(password, BUFSIZ, stdin);
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strip_newline(password);
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puts("\n");
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if (strcmp(user->pw_passwd, password) == 0)
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{
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login_as(user);
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puts("logout\n");
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}
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else
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puts("Invalid password.\n");
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return 0;
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}
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int main(int argc, char** argv)
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{
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if (getuid() != 0)
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{
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fprintf(stderr,
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"%s must be run as root.\nYou are probably looking for the 'su' command, which lets you switch users "
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"once logged in.\n",
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argv[0]);
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return EXIT_FAILURE;
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}
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for (;;)
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{
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if (login()) return EXIT_SUCCESS;
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}
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(void)argc;
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}
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