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/*
Copyright 2022 Sam Anthony
This file is part of samanthony.xyz.
samanthony.xyz 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.
samanthony.xyz 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
samanthony.xyz. If not, see <https://www.gnu.org/licenses/>.
*/
package main
import (
"bufio"
"errors"
"fmt"
"golang.org/x/sys/unix"
"log"
"os"
"runtime"
"strconv"
"strings"
)
func uidOf(user string) (int, error) {
passwdFile, err := os.Open("/etc/passwd")
if err != nil {
return -1, err
}
defer passwdFile.Close()
scanner := bufio.NewScanner(passwdFile)
scanner.Split(bufio.ScanLines)
for scanner.Scan() {
line := scanner.Text()
parsed := strings.Split(line, ":")
name := parsed[0]
if name == user {
uid, err := strconv.Atoi(parsed[2])
if err != nil {
return -1, err
}
return uid, nil
}
}
return -1, errors.New(fmt.Sprintf("user '%s' not in /etc/passwd", user))
}
func gidOf(group string) (int, error) {
groupFile, err := os.Open("/etc/group")
if err != nil {
return -1, err
}
defer groupFile.Close()
scanner := bufio.NewScanner(groupFile)
scanner.Split(bufio.ScanLines)
for scanner.Scan() {
line := scanner.Text()
parsed := strings.Split(line, ":")
name := parsed[0]
if name == group {
gid, err := strconv.Atoi(parsed[2])
if err != nil {
return -1, err
}
return gid, nil
}
}
return -1, errors.New(fmt.Sprintf("group '%s' not in /etc/group", group))
}
func dropPerms(uid, gid int) error {
if runtime.GOOS != "linux" {
if err := unix.Setgid(gid); err != nil {
return errors.New(fmt.Sprintf("setgid(%d): %v", gid, err))
}
if err := unix.Setuid(uid); err != nil {
return errors.New(fmt.Sprintf("setuid(%d): %v", uid, err))
}
return nil
} else {
// setuid/setgid has supposedly been fully supported on Linux
// since go 1.16 but I can't seem to get it to work properly.
log.Print("setgid not supported on Linux, skipping.")
log.Print("setuid not supported on Linux, skipping.")
return nil
}
}
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