77 lines
1.8 KiB
C
77 lines
1.8 KiB
C
/**
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* chkgrp is a program that checks if a user is a member of a group.
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*
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* Author: Johannes Findeisen <you@hanez.org> - 2025
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* Homepage: https://git.xw3.org/hanez/chkgrp
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* License: Apache-2.0 (see LICENSE)
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*/
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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 <pwd.h>
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#include <grp.h>
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#include <unistd.h>
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#include <errno.h>
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#include <limits.h>
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#ifndef LOGIN_NAME_MAX
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#define LOGIN_NAME_MAX 256
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#endif
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int main(int argc, char *argv[])
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{
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if (argc != 3) {
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fprintf(stderr, "Usage: %s <username> <groupname>\n", argv[0]);
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return 2;
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}
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const char *username = argv[1];
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const char *groupname = argv[2];
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// Runtime check for max name length
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long max_name_len = sysconf(_SC_LOGIN_NAME_MAX);
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if (max_name_len <= 0 || max_name_len > 1024) {
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max_name_len = LOGIN_NAME_MAX;
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}
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if (strlen(username) > (size_t)max_name_len) {
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fprintf(stderr, "Error: Username too long (max %ld characters).\n",
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max_name_len);
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return 2;
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}
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if (strlen(groupname) > (size_t)max_name_len) {
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fprintf(stderr, "Error: Group name too long (max %ld characters).\n",
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max_name_len);
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return 2;
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}
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struct passwd *pw = getpwnam(username);
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if (!pw) {
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fprintf(stderr, "Error: User '%s' not found.\n", username);
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return 2;
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}
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struct group *gr = getgrnam(groupname);
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if (!gr) {
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fprintf(stderr, "Error: Group '%s' not found.\n", groupname);
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return 2;
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}
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if (pw->pw_gid == gr->gr_gid) {
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puts("Yes");
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return 0;
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}
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for (char **members = gr->gr_mem; *members != NULL; members++) {
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if (strcmp(*members, username) == 0) {
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puts("Yes");
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return 0;
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}
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}
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puts("No");
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return 1;
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}
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