/*
 * Process identity: max25-bcprd runs unprivileged; init drops from root.
 */
#define _GNU_SOURCE
#include "bcpr/bcpr_runas.h"

#include <errno.h>
#include <grp.h>
#include <pwd.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

int bcpr_runas_refuse_root(int dry_run)
{
    if (geteuid() == 0 && !dry_run) {
        fprintf(stderr,
                "max25-bcprd: refusing to run as root — use max25-bcprd-init "
                "(setuid) for live SER12\n");
        return -1;
    }
    return 0;
}

int bcpr_runas_drop(const bcpr_config_t *cfg)
{
    struct passwd *pw;
    struct group *gr = NULL;
    gid_t gid;
    uid_t uid;
    const char *name;

    if (!cfg || !cfg->run_user[0]) {
        fprintf(stderr, "max25-bcpr: [max25-bcpr] user= required for daemon\n");
        return -1;
    }
    if (geteuid() != 0) {
        fprintf(stderr, "max25-bcpr: privilege drop requires euid=0\n");
        return -1;
    }

    pw = getpwnam(cfg->run_user);
    if (!pw) {
        fprintf(stderr, "max25-bcpr: unknown user=%s\n", cfg->run_user);
        return -1;
    }
    uid = pw->pw_uid;
    gid = pw->pw_gid;
    name = pw->pw_name;

    if (cfg->run_group[0]) {
        gr = getgrnam(cfg->run_group);
        if (!gr) {
            fprintf(stderr, "max25-bcpr: unknown group=%s\n", cfg->run_group);
            return -1;
        }
        gid = gr->gr_gid;
    }

    if (initgroups(name, gid) != 0) {
        fprintf(stderr, "max25-bcpr: initgroups(%s) failed: %s\n", name,
                strerror(errno));
        return -1;
    }
    if (setgid(gid) != 0) {
        fprintf(stderr, "max25-bcpr: setgid failed: %s\n", strerror(errno));
        return -1;
    }
    if (setuid(uid) != 0) {
        fprintf(stderr, "max25-bcpr: setuid failed: %s\n", strerror(errno));
        return -1;
    }
    if (setuid(0) == 0) {
        fprintf(stderr, "max25-bcpr: privilege drop incomplete\n");
        return -1;
    }

    fprintf(stderr, "max25-bcpr: running as uid=%u gid=%u (%s)\n",
            (unsigned)uid, (unsigned)gid, name);
    return 0;
}