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package idtools // import "github.com/docker/docker/pkg/idtools"
import (
"fmt"
"os/exec"
"regexp"
"sort"
"strconv"
"strings"
"sync"
)
// add a user and/or group to Linux /etc/passwd, /etc/group using standard
// Linux distribution commands:
// adduser --system --shell /bin/false --disabled-login --disabled-password --no-create-home --group <username>
// useradd -r -s /bin/false <username>
var (
once sync.Once
userCommand string
idOutRegexp = regexp.MustCompile(`uid=([0-9]+).*gid=([0-9]+)`)
)
const (
// default length for a UID/GID subordinate range
defaultRangeLen = 65536
defaultRangeStart = 100000
)
// AddNamespaceRangesUser takes a username and uses the standard system
// utility to create a system user/group pair used to hold the
// /etc/sub{uid,gid} ranges which will be used for user namespace
// mapping ranges in containers.
func AddNamespaceRangesUser(name string) (int, int, error) {
if err := addUser(name); err != nil {
return -1, -1, fmt.Errorf("error adding user %q: %v", name, err)
}
// Query the system for the created uid and gid pair
out, err := exec.Command("id", name).CombinedOutput()
if err != nil {
return -1, -1, fmt.Errorf("error trying to find uid/gid for new user %q: %v", name, err)
}
matches := idOutRegexp.FindStringSubmatch(strings.TrimSpace(string(out)))
if len(matches) != 3 {
return -1, -1, fmt.Errorf("can't find uid, gid from `id` output: %q", string(out))
}
uid, err := strconv.Atoi(matches[1])
if err != nil {
return -1, -1, fmt.Errorf("can't convert found uid (%s) to int: %v", matches[1], err)
}
gid, err := strconv.Atoi(matches[2])
if err != nil {
return -1, -1, fmt.Errorf("Can't convert found gid (%s) to int: %v", matches[2], err)
}
// Now we need to create the subuid/subgid ranges for our new user/group (system users
// do not get auto-created ranges in subuid/subgid)
if err := createSubordinateRanges(name); err != nil {
return -1, -1, fmt.Errorf("couldn't create subordinate ID ranges: %v", err)
}
return uid, gid, nil
}
func addUser(name string) error {
once.Do(func() {
// set up which commands are used for adding users/groups dependent on distro
if _, err := resolveBinary("adduser"); err == nil {
userCommand = "adduser"
} else if _, err := resolveBinary("useradd"); err == nil {
userCommand = "useradd"
}
})
var args []string
switch userCommand {
case "adduser":
args = []string{"--system", "--shell", "/bin/false", "--no-create-home", "--disabled-login", "--disabled-password", "--group", name}
case "useradd":
args = []string{"-r", "-s", "/bin/false", name}
default:
return fmt.Errorf("cannot add user; no useradd/adduser binary found")
}
if out, err := exec.Command(userCommand, args...).CombinedOutput(); err != nil {
return fmt.Errorf("failed to add user with error: %v; output: %q", err, string(out))
}
return nil
}
func createSubordinateRanges(name string) error {
// first, we should verify that ranges weren't automatically created
// by the distro tooling
ranges, err := parseSubuid(name)
if err != nil {
return fmt.Errorf("error while looking for subuid ranges for user %q: %v", name, err)
}
if len(ranges) == 0 {
// no UID ranges; let's create one
startID, err := findNextUIDRange()
if err != nil {
return fmt.Errorf("can't find available subuid range: %v", err)
}
idRange := fmt.Sprintf("%d-%d", startID, startID+defaultRangeLen-1)
out, err := exec.Command("usermod", "-v", idRange, name).CombinedOutput()
if err != nil {
return fmt.Errorf("unable to add subuid range to user: %q; output: %s, err: %v", name, out, err)
}
}
ranges, err = parseSubgid(name)
if err != nil {
return fmt.Errorf("error while looking for subgid ranges for user %q: %v", name, err)
}
if len(ranges) == 0 {
// no GID ranges; let's create one
startID, err := findNextGIDRange()
if err != nil {
return fmt.Errorf("can't find available subgid range: %v", err)
}
idRange := fmt.Sprintf("%d-%d", startID, startID+defaultRangeLen-1)
out, err := exec.Command("usermod", "-w", idRange, name).CombinedOutput()
if err != nil {
return fmt.Errorf("unable to add subgid range to user: %q; output: %s, err: %v", name, out, err)
}
}
return nil
}
func findNextUIDRange() (int, error) {
ranges, err := parseSubuid("ALL")
if err != nil {
return -1, fmt.Errorf("couldn't parse all ranges in /etc/subuid file: %v", err)
}
sort.Sort(ranges)
return findNextRangeStart(ranges)
}
func findNextGIDRange() (int, error) {
ranges, err := parseSubgid("ALL")
if err != nil {
return -1, fmt.Errorf("couldn't parse all ranges in /etc/subgid file: %v", err)
}
sort.Sort(ranges)
return findNextRangeStart(ranges)
}
func findNextRangeStart(rangeList ranges) (int, error) {
startID := defaultRangeStart
for _, arange := range rangeList {
if wouldOverlap(arange, startID) {
startID = arange.Start + arange.Length
}
}
return startID, nil
}
func wouldOverlap(arange subIDRange, ID int) bool {
low := ID
high := ID + defaultRangeLen
if (low >= arange.Start && low <= arange.Start+arange.Length) ||
(high <= arange.Start+arange.Length && high >= arange.Start) {
return true
}
return false
}
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