moby/pkg/idtools/usergroupadd_linux.go
Phil Estes c6f45fd2ee Lazy init useradd and remove init()
This should not have been in init() as it causes these lookups to happen
in all reexecs of the Docker binary. The only time it needs to be
resolved is when a user is added, which is extremely rare.

Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com>
2016-04-06 17:53:45 -04:00

188 lines
5.6 KiB
Go

package idtools
import (
"fmt"
"os/exec"
"path/filepath"
"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
cmdTemplates = map[string]string{
"adduser": "--system --shell /bin/false --no-create-home --disabled-login --disabled-password --group %s",
"useradd": "-r -s /bin/false %s",
"usermod": "-%s %d-%d %s",
}
idOutRegexp = regexp.MustCompile(`uid=([0-9]+).*gid=([0-9]+)`)
// default length for a UID/GID subordinate range
defaultRangeLen = 65536
defaultRangeStart = 100000
userMod = "usermod"
)
func resolveBinary(binname string) (string, error) {
binaryPath, err := exec.LookPath(binname)
if err != nil {
return "", err
}
resolvedPath, err := filepath.EvalSymlinks(binaryPath)
if err != nil {
return "", err
}
//only return no error if the final resolved binary basename
//matches what was searched for
if filepath.Base(resolvedPath) == binname {
return resolvedPath, nil
}
return "", fmt.Errorf("Binary %q does not resolve to a binary of that name in $PATH (%q)", binname, resolvedPath)
}
// 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 := execCmd("id", name)
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(userName 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"
}
})
if userCommand == "" {
return fmt.Errorf("Cannot add user; no useradd/adduser binary found")
}
args := fmt.Sprintf(cmdTemplates[userCommand], userName)
out, err := execCmd(userCommand, args)
if 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)
}
out, err := execCmd(userMod, fmt.Sprintf(cmdTemplates[userMod], "v", startID, startID+defaultRangeLen-1, name))
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)
}
out, err := execCmd(userMod, fmt.Sprintf(cmdTemplates[userMod], "w", startID, startID+defaultRangeLen-1, name))
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
}
func execCmd(cmd, args string) ([]byte, error) {
execCmd := exec.Command(cmd, strings.Split(args, " ")...)
return execCmd.CombinedOutput()
}