registeremail/email.c

/*
        RegisterEmail A webservice for selfhosted email servers to make it easy registering Emails (And optionally Enabling SSH)
        Copyright (C) 2024 Mike Nolan

        This program is free software: you can redistribute it and/or modify
        it under the terms of the GNU General Public License as published by
        the Free Software Foundation, either version 3 of the License, or
        (at your option) any later version.

        This program is distributed in the hope that it will be useful,
        but WITHOUT ANY WARRANTY; without even the implied warranty of
        MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
        GNU General Public License for more details.

        You should have received a copy of the GNU General Public License
        along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/
#include <jansson.h>
#include <stdio.h>
#include <sysexits.h>
#include <string.h>
#include <sys/types.h>
#include <pwd.h>
#include <shadow.h>
#include <crypt.h>
#include <stdbool.h>
const char* required_user = "tesses";
const char* mail = "mail";
const char* deny_group = "no_ssh";
const char* sudoer_group = "sudo";
void create_user(const char* username, const char* password, const char* fullname)
{
    char cmdline[1024];
    snprintf(cmdline,sizeof(cmdline),"/sbin/adduser %s",username);
    FILE* f=popen(cmdline,"w");
    fprintf(f,"%s\n%s\n%s\n\n\n\n\ny\n",password,password,fullname);
    fflush(f);
    fclose(f);
    
    snprintf(cmdline,sizeof(cmdline),"/sbin/usermod -aG %s %s",mail, username);
    system(cmdline);
}
void block_ssh(const char* username)
{
    char cmdline[1024];
    snprintf(cmdline,sizeof(cmdline),"/sbin/usermod -aG %s %s",deny_group,username);
    system(cmdline);
}

void enable_sudo(const char* username)
{
    char cmdline[1024];
    snprintf(cmdline,sizeof(cmdline),"/sbin/usermod -aG %s %s",sudoer_group,username);
    system(cmdline);
}
//https://stackoverflow.com/a/63173069
bool password_correct(const char* user, const char* password)
{
    struct passwd* passwdEntry = getpwnam( user );
    if ( !passwdEntry )
    {
        printf( "User '%s' doesn't exist\n", user );
        return false;
    }

    if ( 0 != strcmp( passwdEntry->pw_passwd, "x" ) )
    {
        return strcmp( passwdEntry->pw_passwd, crypt( password, passwdEntry->pw_passwd ) ) == 0;
    }
    else
    {
        // password is in shadow file
        struct spwd* shadowEntry = getspnam( user );
        if ( !shadowEntry )
        {
            printf( "Failed to read shadow entry for user '%s'\n", user );
            return false;
        }

        return strcmp( shadowEntry->sp_pwdp, crypt( password, shadowEntry->sp_pwdp ) ) == 0;
    }
}
int main(int argc,char** argv)
{
    struct json_t* json=json_loadf(stdin,0,NULL);
    if(json)
    {
        struct json_t* username= json_object_get(json,"username");
        struct json_t* password=json_object_get(json,"password");
        struct json_t* admin_username = json_object_get(json,"admin_user");
        struct json_t* admin_password = json_object_get(json,"admin_pass");
        struct json_t* full_name = json_object_get(json,"fullname");
        struct json_t* has_sudo = json_object_get(json,"has_sudo");
        struct json_t* can_login_ssh = json_object_get(json,"can_login_ssh");

        if(json_typeof(username) == JSON_STRING && json_typeof(password) == JSON_STRING && json_typeof(admin_username) == JSON_STRING && json_typeof(admin_password) == JSON_STRING && json_typeof(full_name) == JSON_STRING)
        {
            if(json_string_length(username) > 256) return 1; 
            const char* _username = json_string_value(username);
            const char* _password = json_string_value(password);
            const char* _admin_user = json_string_value(admin_username);
            const char* _admin_pass = json_string_value(admin_password);
            const char* _fullname = json_string_value(full_name);
            if(strcmp(_admin_user,required_user) != 0 || !password_correct(_admin_user,_admin_pass))
            {
                return EX_NOPERM;
            }
            create_user(_username,_password,_fullname);
            if(json_typeof(has_sudo) == JSON_TRUE)
            {
                enable_sudo(_username);
            }

            if(json_typeof(can_login_ssh) == JSON_FALSE)
            {
                block_ssh(_username);
            }
            
            json_decref(json);
            return 0;
        }
        

        json_decref(json);

        return EX_DATAERR;
    }
    return EX_DATAERR;
}