104 lines
3.0 KiB
C
104 lines
3.0 KiB
C
#define _GNU_SOURCE /* See feature_test_macros(7) */
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#include <stdio.h>
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#include <stdlib.h>
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#include <stdbool.h>
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#include <unistd.h>
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#include <string.h>
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#include <sys/types.h>
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bool check_user(char *filename, char *username, unsigned long *new_start) {
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/*
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* Check whether the user exists in the uid file (subuid, subgid).
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* Return exists or not, and set the new_start if need it.
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*
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* Args:
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* filename (char *): means the uid file (subuid or subgid).
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* username (char *): the user who run this excutable file.
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* new_start (unsigned long *): it's a pointer, save the new start point.
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* Return:
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* exist (bool): exist or not
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*/
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FILE *fp = fopen(filename, "r");
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if (fp == NULL) {
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printf("[ERROR] Please contact Unix Manager.\n");
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exit(1);
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}
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// read data from subuid, subgid
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char line[100];
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char user[30];
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unsigned long start, size; // 0~2^32-1, equal to subuid
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bool exist = false;
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while (fgets(line, sizeof(line), fp)) {
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sscanf(line, "%[^:]:%lu:%lu", user, &start, &size);
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*new_start = start + size;
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if (strcmp(username, user) == 0) exist = true;
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}
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fclose(fp);
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return exist;
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}
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void insert_user(char *filename, char *username, unsigned long start) {
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/*
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* Insert the user into uid file
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* It will setup the next start uid automatically
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* == it will change /etc/subuid or /etc/subgid ==
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*
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* Args:
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* filename (char *): means the uid file (subuid or subgid).
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* username (char *): the user who run this excutable file.
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* new_start (unsigned long ): it's a value, means the next start uid
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* Return:
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* No
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*/
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FILE *fp = fopen(filename, "a");
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if (fp == NULL) {
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printf("[ERROR] Please contact Unix Manager.\n");
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exit(1);
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}
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char new_line[100];
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sprintf(new_line, "%s:%lu:%d\n", username, start, 65536);
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fputs(new_line, fp);
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fclose(fp);
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printf("[SUCCESS] %s has been inserted in %s\n", username, filename);
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}
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int main() {
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int ret;
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char *username = getlogin();
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uid_t ruid, euid, suid;
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getresuid(&ruid, &euid, &suid);
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printf("ruid=%d, euid=%d, suid=%d\n", ruid, euid, suid);
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ret = setuid(0);
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printf("ret=%d\n", ret);
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if (ret != 0) {
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perror("Error:");
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exit(1);
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}
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getresuid(&ruid, &euid, &suid);
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printf("ruid=%d, euid=%d, suid=%d\n", ruid, euid, suid);
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char filenames[2][20] = {
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"/etc/subuid", "/etc/subgid"
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};
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bool exist;
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unsigned long new_start; // 0~2^32-1, equal to subuid
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for (int i=0; i<2; i++) {
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new_start = 100000; // subuid, subgid default from 100000~165535
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exist = check_user(filenames[i], username, &new_start);
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if (exist) {
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printf("[WARNING] %s has been in %s, no change\n", username, filenames[i]);
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} else {
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insert_user(filenames[i], username, new_start);
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}
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}
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return 0;
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}
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