utils-std

id.c (6333B)

// utils-std: Collection of commonly available Unix tools
// SPDX-FileCopyrightText: 2017 Haelwenn (lanodan) Monnier <contact+utils@hacktivis.me>
// SPDX-License-Identifier: MPL-2.0
#define _DEFAULT_SOURCE // getgrouplist (4.4BSD+)
#include <grp.h>        // getgrgid, getgroups, getgrouplist(glibc)
#include <pwd.h>        // getpwuid
#include <stdbool.h>    // bool
#include <stdio.h>      // printf, perror
#include <stdlib.h>     // calloc, free
#include <sys/types.h>  // uid_t
#include <unistd.h>     // getuid, getgid, getopt, opt*, getgrouplist(FreeBSD, NetBSD)
const char *argv0 = "id";
bool name_flag = false;
static int
simple_list_groups(struct passwd *pw, int ngroups, gid_t *groups)
{
	bool first = true;
	// Don't print basegid twice when present in pw and grouplist
	bool basegid_done = false;
	for(int i = 0; i < ngroups; i++)
	{
		if(groups[i] == pw->pw_gid)
		{
			if(basegid_done)
				continue;
			else
				basegid_done = true;
		}
		if(name_flag)
		{
			struct group *lgr = getgrgid(groups[i]);
			if(lgr == NULL) return 1;
			if(!first) putchar(' ');
			printf("%s", lgr->gr_name);
		}
		else
		{
			if(!first) putchar(' ');
			printf("%u", groups[i]);
		}
		first = false;
	}
	putchar('\n');
	return 0;
}
static int
list_groups(struct passwd *pw, int ngroups, gid_t *groups)
{
	bool first = true;
	// Don't print basegid twice when present in pw and grouplist
	bool basegid_done = false;
	printf(" groups=");
	for(int i = 0; i < ngroups; i++)
	{
		struct group *lgr = getgrgid(groups[i]);
		if(groups[i] == pw->pw_gid)
		{
			if(basegid_done)
				continue;
			else
				basegid_done = true;
		}
		if(name_flag)
		{
			if(lgr == NULL) return 1;
			if(!first) putchar(' ');
			printf("%s", lgr->gr_name);
		}
		else
		{
			if(!first) putchar(',');
			printf("%u", groups[i]);
			if(lgr != NULL) printf("(%s)", lgr->gr_name);
		}
		first = false;
	}
	putchar('\n');
	return 0;
}
static int
print_gid(const char *field, struct group *gr, gid_t gid)
{
	if(gr && gr->gr_name)
	{
		if(name_flag) return printf("%s=%s", field, gr->gr_name);
		return printf("%s=%u(%s)", field, gid, gr->gr_name);
	}
	else
	{
		if(name_flag) return -1;
		return printf("%s=%u", field, gid);
	}
}
static int
print_uid(const char *field, struct passwd *pw, uid_t uid)
{
	if(pw && pw->pw_name)
	{
		if(name_flag) return printf("%s=%s", field, pw->pw_name);
		return printf("%s=%u(%s)", field, uid, pw->pw_name);
	}
	else
	{
		if(name_flag) return -1;
		return printf("%s=%u", field, uid);
	}
}
static void
safe_getpwuid(uid_t uid, struct passwd *res)
{
	struct passwd *pw = getpwuid(uid);
	if(pw != NULL) *res = *pw;
}
enum id_modes
{
	ID_NORMAL,
	ID_GROUPS,
	ID_GID,
	ID_UID,
};
static void
usage(void)
{
	fprintf(stderr, "Usage: id [-Ggu] [-nr] [user]\n");
}
int
main(int argc, char *argv[])
{
	int ret = 0;
	enum id_modes mode = ID_NORMAL;
	bool real_flag = false;
	int ngroups = 0;
	int ngroups_max = (int)sysconf(_SC_NGROUPS_MAX) + 1;
	if(ngroups_max <= 0)
	{
		perror("id: error: sysconf(_SC_NGROUPS_MAX)");
		return 1;
	}
	gid_t *groups = NULL;
	groups = calloc(ngroups_max, sizeof(*groups));
	if(groups == NULL)
	{
		perror("id: error: calloc(groups)");
		return 1;
	}
	// geteuid, getuid, getegid, getgid shall always be successful
	uid_t uid = getuid();
	uid_t euid = geteuid();
	gid_t gid = getgid();
	gid_t egid = getegid();
	struct passwd pw = {.pw_uid = uid, .pw_gid = gid};
	struct passwd epw = {.pw_uid = euid, .pw_gid = egid};
	for(int c = -1; (c = getopt(argc, argv, ":Ggunr")) != -1;)
	{
		switch(c)
		{
		case 'G':
			mode = ID_GROUPS;
			break;
		case 'u':
			mode = ID_UID;
			break;
		case 'g':
			mode = ID_GID;
			break;
		case 'n':
			name_flag = true;
			break;
		case 'r':
			real_flag = true;
			break;
		case '?':
			fprintf(stderr, "%s: error: Unhandled option '-%c'\n", argv0, optopt);
			usage();
			free(groups);
			return 1;
		default:
			fprintf(stderr, "%s: error: Unhandled getopt case '%c'\n", argv0, c);
			usage();
			free(groups);
			return 1;
		}
	}
	argc -= optind;
	argv += optind;
	if(argc == 0)
	{
		safe_getpwuid(uid, &pw);
		safe_getpwuid(euid, &epw);
		// Get groups from currently running process instead of configuration
		ngroups = getgroups(ngroups_max, groups);
		if(ngroups < 0)
		{
			perror("id: error: getgroups");
			goto failure;
		}
	}
	else if(argc == 1)
	{
		struct passwd *pw_n = getpwnam(argv[0]);
		if(pw_n == NULL)
		{
			goto failure;
		}
		pw = *pw_n;
		epw = *pw_n;
		uid = pw.pw_uid;
		euid = epw.pw_uid;
		gid = pw.pw_gid;
		egid = epw.pw_gid;
		// Can only get groups from configuration
		if(getgrouplist(pw.pw_name, pw.pw_gid, groups, &ngroups_max) < 0)
		{
			perror("id: error: getgrouplist");
			goto failure;
		}
		ngroups = ngroups_max;
	}
	else
	{
		usage();
	}
	struct group *gr = getgrgid(gid);
	struct group *egr = getgrgid(egid);
	if(mode == ID_GID)
	{
		if(!real_flag) gid = egid;
		if(!name_flag)
		{
			ret = printf("%u\n", gid);
		}
		else
		{
			if(gr == NULL || gr->gr_name == NULL)
			{
				ret--;
				fprintf(stderr, "%s: error: Cannot find name for group ID %u\n", argv0, gid);
				printf("%u\n", gid);
			}
			else
			{
				ret = printf("%s\n", gr->gr_name);
			}
		}
		if(ret < 0) goto failure;
		goto done;
	}
	if(mode == ID_UID)
	{
		if(!real_flag) uid = euid;
		if(!name_flag)
		{
			ret = printf("%u\n", uid);
		}
		else
		{
			if(pw.pw_name == NULL)
			{
				ret--;
				fprintf(stderr, "%s: error: Cannot find name for user ID %u\n", argv0, uid);
				printf("%u\n", uid);
			}
			else
			{
				ret = printf("%s\n", pw.pw_name);
			}
		}
		if(ret < 0) goto failure;
		goto done;
	}
	if(mode == ID_GROUPS)
	{
		if(real_flag)
		{
			ret = simple_list_groups(&pw, ngroups, groups);
		}
		else
		{
			ret = simple_list_groups(&epw, ngroups, groups);
		}
		if(ret != 0) goto failure;
		goto done;
	}
	ret = print_uid("uid", &pw, uid);
	if(ret < 0) goto failure;
	if(euid != uid)
	{
		ret = print_uid(" euid", &epw, euid);
		if(ret < 0) goto failure;
	}
	ret = print_gid(" gid", gr, gid);
	if(ret < 0) goto failure;
	if(egid != gid)
	{
		ret = print_gid(" egid", egr, egid);
		if(ret < 0) goto failure;
	}
	if(list_groups(&pw, ngroups, groups) != 0) goto failure;
	ret = printf("\n");
	if(ret < 0) goto failure;
done:
	free(groups);
	return 0;
failure:
	free(groups);
	return 1;
}