Program: CWE-862
Project: CVE-2019-12875
Buggy source:
/* abuild-sudo.c - limited root privileges for users in "abuild" group
 *
 * Copyright (C) 2012 Natanael Copa <ncopa@alpinelinux.org>
 * All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published
 * by the Free Software Foundation. See http://www.gnu.org/ for details.
 */

#include <sys/types.h>

#include <err.h>
#include <grp.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#ifndef ABUILD_GROUP
#define ABUILD_GROUP "abuild"
#endif

static const char* valid_cmds[] = {
	"/bin/adduser",
	"/usr/sbin/adduser",
	"/bin/addgroup",
	"/usr/sbin/addgroup",
	"/sbin/apk",
	"/usr/bin/abuild-rmtemp",
	NULL
};

const char *get_command_path(const char *cmd)
{
	const char *p;
	int i;
	for (i = 0; valid_cmds[i] != NULL; i++) {
		if (access(valid_cmds[i], F_OK) == -1)
			continue;
		p = strrchr(valid_cmds[i], '/') + 1;
		if (strcmp(p, cmd) == 0)
			return valid_cmds[i];
	}
	return NULL;
}

int is_in_group(gid_t group)
{
	int ngroups_max = sysconf(_SC_NGROUPS_MAX) + 1;
	gid_t *buf = malloc(ngroups_max * sizeof(gid_t));
	int ngroups;
	int i;
	if (buf == NULL) {
		perror("malloc");
		return 0;
	}
	ngroups = getgroups(ngroups_max, buf);
	for (i = 0; i < ngroups; i++) {
		if (buf[i] == group)
			break;
	}
	free(buf);
	return i < ngroups;
}

int main(int argc, const char *argv[])
{
	struct group *grent;
	const char *cmd;
	const char *path;
	int i;
	struct passwd *pw;

	grent = getgrnam(ABUILD_GROUP);
	if (grent == NULL)
		errx(1, "%s: Group not found", ABUILD_GROUP);

	char *name = NULL;
	pw = getpwuid(getuid());
	if (pw)
		name = pw->pw_name;

	if (!is_in_group(grent->gr_gid)) {
		errx(1, "User %s is not a member of group %s\n",
			name ? name : "(unknown)", ABUILD_GROUP);
	}

	if (name == NULL)
		warnx("Could not find username for uid %d\n", getuid());
	setenv("USER", name ?: "", 1);

	cmd = strrchr(argv[0], '/');
	if (cmd)
		cmd++;
	else
		cmd = argv[0];
	cmd = strchr(cmd, '-');
	if (cmd == NULL)
		errx(1, "Calling command has no '-'");
	cmd++;

	path = get_command_path(cmd);
	if (path == NULL)
		errx(1, "%s: Not a valid subcommand", cmd);

	/* we dont allow --allow-untrusted option */
	for (i = 1; i < argc; i++)
		if (strcmp(argv[i], "--allow-untrusted") == 0)
			errx(1, "%s: not allowed option", "--allow-untrusted");

	argv[0] = path;
	/* set our uid to root so bbsuid --install works */
	setuid(0);
	/* set our gid to root so apk commit hooks run with the same gid as for "sudo apk add ..." */
	setgid(0);
	execv(path, (char * const*)argv);
	perror(path);
	return 1;
}


Fixed version (ground truth):
/* abuild-sudo.c - limited root privileges for users in "abuild" group
 *
 * Copyright (C) 2012 Natanael Copa <ncopa@alpinelinux.org>
 * All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published
 * by the Free Software Foundation. See http://www.gnu.org/ for details.
 */

#include <sys/types.h>

#include <err.h>
#include <grp.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#ifndef ABUILD_GROUP
#define ABUILD_GROUP "abuild"
#endif

static const char* valid_cmds[] = {
	"/bin/adduser",
	"/usr/sbin/adduser",
	"/bin/addgroup",
	"/usr/sbin/addgroup",
	"/sbin/apk",
	"/usr/bin/abuild-rmtemp",
	NULL
};

static const char* invalid_opts[] = {
	"--allow-untrusted",
	"--keys-dir",
	NULL,
};

const char *get_command_path(const char *cmd)
{
	const char *p;
	int i;
	for (i = 0; valid_cmds[i] != NULL; i++) {
		if (access(valid_cmds[i], F_OK) == -1)
			continue;
		p = strrchr(valid_cmds[i], '/') + 1;
		if (strcmp(p, cmd) == 0)
			return valid_cmds[i];
	}
	return NULL;
}

void check_option(const char *opt)
{
	int i;
	for (i = 0; invalid_opts[i] != NULL; i++)
		if (strcmp(opt, invalid_opts[i]) == 0)
			errx(1, "%s: not allowed option", opt);
}

int is_in_group(gid_t group)
{
	int ngroups_max = sysconf(_SC_NGROUPS_MAX) + 1;
	gid_t *buf = malloc(ngroups_max * sizeof(gid_t));
	int ngroups;
	int i;
	if (buf == NULL) {
		perror("malloc");
		return 0;
	}
	ngroups = getgroups(ngroups_max, buf);
	for (i = 0; i < ngroups; i++) {
		if (buf[i] == group)
			break;
	}
	free(buf);
	return i < ngroups;
}

int main(int argc, const char *argv[])
{
	struct group *grent;
	const char *cmd;
	const char *path;
	int i;
	struct passwd *pw;

	grent = getgrnam(ABUILD_GROUP);
	if (grent == NULL)
		errx(1, "%s: Group not found", ABUILD_GROUP);

	char *name = NULL;
	pw = getpwuid(getuid());
	if (pw)
		name = pw->pw_name;

	if (!is_in_group(grent->gr_gid)) {
		errx(1, "User %s is not a member of group %s\n",
			name ? name : "(unknown)", ABUILD_GROUP);
	}

	if (name == NULL)
		warnx("Could not find username for uid %d\n", getuid());
	setenv("USER", name ?: "", 1);

	cmd = strrchr(argv[0], '/');
	if (cmd)
		cmd++;
	else
		cmd = argv[0];
	cmd = strchr(cmd, '-');
	if (cmd == NULL)
		errx(1, "Calling command has no '-'");
	cmd++;

	path = get_command_path(cmd);
	if (path == NULL)
		errx(1, "%s: Not a valid subcommand", cmd);

	for (i = 1; i < argc; i++)
		check_option(argv[i]);

	argv[0] = path;
	/* set our uid to root so bbsuid --install works */
	setuid(0);
	/* set our gid to root so apk commit hooks run with the same gid as for "sudo apk add ..." */
	setgid(0);
	execv(path, (char * const*)argv);
	perror(path);
	return 1;
}