Change subordinate range-owning user to be a system user
Change user/group creation to use flags to adduser/useradd to enforce it being a system user. Use system user defaults that auto-create a matching group. These changes allow us to remove all group creation code, and in doing so we also removed the code that finds available uid, gid integers and use post-creation query to gather the system-generated uid and gid. The only added complexity is that today distros don't auto-create subordinate ID ranges for a new ID if it is a system ID, so we now need to handle finding a free range and then calling the `usermod` tool to add the ranges for that ID. Note that this requires the distro supports the `-v` and `-w` flags on `usermod` for subordinate ID range additions. Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp)
This commit is contained in:
Phil Estes
parent
45b2a57d1c
commit
c18e7f3a04
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@ -155,6 +155,9 @@ func parseSubgid(username string) (ranges, error) {
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return parseSubidFile(subgidFileName, username)
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}
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// parseSubidFile will read the appropriate file (/etc/subuid or /etc/subgid)
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// and return all found ranges for a specified username. If the special value
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// "ALL" is supplied for username, then all ranges in the file will be returned
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func parseSubidFile(path, username string) (ranges, error) {
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var rangeList ranges
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@ -178,8 +181,7 @@ func parseSubidFile(path, username string) (ranges, error) {
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if len(parts) != 3 {
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return rangeList, fmt.Errorf("Cannot parse subuid/gid information: Format not correct for %s file", path)
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}
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if parts[0] == username {
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// return the first entry for a user; ignores potential for multiple ranges per user
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if parts[0] == username || username == "ALL" {
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startid, err := strconv.Atoi(parts[1])
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if err != nil {
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return rangeList, fmt.Errorf("String to int conversion failed during subuid/gid parsing of %s: %v", path, err)
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@ -4,31 +4,31 @@ import (
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"fmt"
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"os/exec"
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"path/filepath"
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"regexp"
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"sort"
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"strconv"
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"strings"
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"syscall"
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)
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// add a user and/or group to Linux /etc/passwd, /etc/group using standard
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// Linux distribution commands:
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// adduser --uid <id> --shell /bin/login --no-create-home --disabled-login --ingroup <groupname> <username>
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// useradd -M -u <id> -s /bin/nologin -N -g <groupname> <username>
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// addgroup --gid <id> <groupname>
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// groupadd -g <id> <groupname>
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const baseUID int = 10000
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const baseGID int = 10000
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const idMAX int = 65534
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// adduser --system --shell /bin/false --disabled-login --disabled-password --no-create-home --group <username>
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// useradd -r -s /bin/false <username>
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var (
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userCommand string
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groupCommand string
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userCommand string
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cmdTemplates = map[string]string{
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"adduser": "--uid %d --shell /bin/false --no-create-home --disabled-login --ingroup %s %s",
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"useradd": "-M -u %d -s /bin/false -N -g %s %s",
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"addgroup": "--gid %d %s",
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"groupadd": "-g %d %s",
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"adduser": "--system --shell /bin/false --no-create-home --disabled-login --disabled-password --group %s",
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"useradd": "-r -s /bin/false %s",
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"usermod": "-%s %d-%d %s",
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}
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idOutRegexp = regexp.MustCompile(`uid=([0-9]+).*gid=([0-9]+)`)
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// default length for a UID/GID subordinate range
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defaultRangeLen = 65536
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defaultRangeStart = 100000
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userMod = "usermod"
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)
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func init() {
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@ -38,11 +38,6 @@ func init() {
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} else if _, err := resolveBinary("useradd"); err == nil {
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userCommand = "useradd"
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}
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if _, err := resolveBinary("addgroup"); err == nil {
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groupCommand = "addgroup"
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} else if _, err := resolveBinary("groupadd"); err == nil {
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groupCommand = "groupadd"
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}
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}
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func resolveBinary(binname string) (string, error) {
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@ -62,94 +57,132 @@ func resolveBinary(binname string) (string, error) {
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return "", fmt.Errorf("Binary %q does not resolve to a binary of that name in $PATH (%q)", binname, resolvedPath)
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}
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// AddNamespaceRangesUser takes a name and finds an unused uid, gid pair
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// and calls the appropriate helper function to add the group and then
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// the user to the group in /etc/group and /etc/passwd respectively.
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// This new user's /etc/sub{uid,gid} ranges will be used for user namespace
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// AddNamespaceRangesUser takes a username and uses the standard system
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// utility to create a system user/group pair used to hold the
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// /etc/sub{uid,gid} ranges which will be used for user namespace
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// mapping ranges in containers.
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func AddNamespaceRangesUser(name string) (int, int, error) {
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// Find unused uid, gid pair
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uid, err := findUnusedUID(baseUID)
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if err != nil {
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return -1, -1, fmt.Errorf("Unable to find unused UID: %v", err)
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}
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gid, err := findUnusedGID(baseGID)
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if err != nil {
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return -1, -1, fmt.Errorf("Unable to find unused GID: %v", err)
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if err := addUser(name); err != nil {
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return -1, -1, fmt.Errorf("Error adding user %q: %v", name, err)
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}
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// First add the group that we will use
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if err := addGroup(name, gid); err != nil {
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return -1, -1, fmt.Errorf("Error adding group %q: %v", name, err)
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// Query the system for the created uid and gid pair
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out, err := execCmd("id", name)
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if err != nil {
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return -1, -1, fmt.Errorf("Error trying to find uid/gid for new user %q: %v", name, err)
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}
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// Add the user as a member of the group
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if err := addUser(name, uid, name); err != nil {
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return -1, -1, fmt.Errorf("Error adding user %q: %v", name, err)
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matches := idOutRegexp.FindStringSubmatch(strings.TrimSpace(string(out)))
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if len(matches) != 3 {
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return -1, -1, fmt.Errorf("Can't find uid, gid from `id` output: %q", string(out))
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}
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uid, err := strconv.Atoi(matches[1])
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if err != nil {
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return -1, -1, fmt.Errorf("Can't convert found uid (%s) to int: %v", matches[1], err)
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}
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gid, err := strconv.Atoi(matches[2])
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if err != nil {
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return -1, -1, fmt.Errorf("Can't convert found gid (%s) to int: %v", matches[2], err)
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}
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// Now we need to create the subuid/subgid ranges for our new user/group (system users
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// do not get auto-created ranges in subuid/subgid)
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if err := createSubordinateRanges(name); err != nil {
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return -1, -1, fmt.Errorf("Couldn't create subordinate ID ranges: %v", err)
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}
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return uid, gid, nil
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}
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func addUser(userName string, uid int, groupName string) error {
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func addUser(userName string) error {
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if userCommand == "" {
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return fmt.Errorf("Cannot add user; no useradd/adduser binary found")
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}
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args := fmt.Sprintf(cmdTemplates[userCommand], uid, groupName, userName)
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return execAddCmd(userCommand, args)
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}
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func addGroup(groupName string, gid int) error {
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if groupCommand == "" {
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return fmt.Errorf("Cannot add group; no groupadd/addgroup binary found")
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}
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args := fmt.Sprintf(cmdTemplates[groupCommand], gid, groupName)
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// only error out if the error isn't that the group already exists
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// if the group exists then our needs are already met
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if err := execAddCmd(groupCommand, args); err != nil && !strings.Contains(err.Error(), "already exists") {
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return err
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}
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return nil
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}
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func execAddCmd(cmd, args string) error {
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execCmd := exec.Command(cmd, strings.Split(args, " ")...)
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out, err := execCmd.CombinedOutput()
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args := fmt.Sprintf(cmdTemplates[userCommand], userName)
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out, err := execCmd(userCommand, args)
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if err != nil {
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return fmt.Errorf("Failed to add user/group with error: %v; output: %q", err, string(out))
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return fmt.Errorf("Failed to add user with error: %v; output: %q", err, string(out))
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}
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return nil
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}
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func findUnusedUID(startUID int) (int, error) {
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return findUnused("passwd", startUID)
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}
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func createSubordinateRanges(name string) error {
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func findUnusedGID(startGID int) (int, error) {
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return findUnused("group", startGID)
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}
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func findUnused(file string, id int) (int, error) {
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for {
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cmdStr := fmt.Sprintf("cat /etc/%s | cut -d: -f3 | grep '^%d$'", file, id)
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cmd := exec.Command("sh", "-c", cmdStr)
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if err := cmd.Run(); err != nil {
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// if a non-zero return code occurs, then we know the ID was not found
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// and is usable
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if exiterr, ok := err.(*exec.ExitError); ok {
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// The program has exited with an exit code != 0
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if status, ok := exiterr.Sys().(syscall.WaitStatus); ok {
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if status.ExitStatus() == 1 {
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//no match, we can use this ID
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return id, nil
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}
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}
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}
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return -1, fmt.Errorf("Error looking in /etc/%s for unused ID: %v", file, err)
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// first, we should verify that ranges weren't automatically created
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// by the distro tooling
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ranges, err := parseSubuid(name)
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if err != nil {
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return fmt.Errorf("Error while looking for subuid ranges for user %q: %v", name, err)
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}
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if len(ranges) == 0 {
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// no UID ranges; let's create one
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startID, err := findNextUIDRange()
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if err != nil {
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return fmt.Errorf("Can't find available subuid range: %v", err)
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}
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id++
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if id > idMAX {
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return -1, fmt.Errorf("Maximum id in %q reached with finding unused numeric ID", file)
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out, err := execCmd(userMod, fmt.Sprintf(cmdTemplates[userMod], "v", startID, startID+defaultRangeLen-1, name))
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if err != nil {
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return fmt.Errorf("Unable to add subuid range to user: %q; output: %s, err: %v", name, out, err)
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}
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}
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ranges, err = parseSubgid(name)
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if err != nil {
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return fmt.Errorf("Error while looking for subgid ranges for user %q: %v", name, err)
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}
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if len(ranges) == 0 {
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// no GID ranges; let's create one
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startID, err := findNextGIDRange()
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if err != nil {
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return fmt.Errorf("Can't find available subgid range: %v", err)
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}
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out, err := execCmd(userMod, fmt.Sprintf(cmdTemplates[userMod], "w", startID, startID+defaultRangeLen-1, name))
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if err != nil {
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return fmt.Errorf("Unable to add subgid range to user: %q; output: %s, err: %v", name, out, err)
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}
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}
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return nil
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}
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func findNextUIDRange() (int, error) {
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ranges, err := parseSubuid("ALL")
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if err != nil {
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return -1, fmt.Errorf("Couldn't parse all ranges in /etc/subuid file: %v", err)
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}
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sort.Sort(ranges)
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return findNextRangeStart(ranges)
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}
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func findNextGIDRange() (int, error) {
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ranges, err := parseSubgid("ALL")
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if err != nil {
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return -1, fmt.Errorf("Couldn't parse all ranges in /etc/subgid file: %v", err)
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}
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sort.Sort(ranges)
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return findNextRangeStart(ranges)
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}
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func findNextRangeStart(rangeList ranges) (int, error) {
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startID := defaultRangeStart
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for _, arange := range rangeList {
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if wouldOverlap(arange, startID) {
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startID = arange.Start + arange.Length
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}
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}
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return startID, nil
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}
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func wouldOverlap(arange subIDRange, ID int) bool {
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low := ID
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high := ID + defaultRangeLen
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if (low >= arange.Start && low <= arange.Start+arange.Length) ||
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(high <= arange.Start+arange.Length && high >= arange.Start) {
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return true
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}
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return false
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}
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func execCmd(cmd, args string) ([]byte, error) {
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execCmd := exec.Command(cmd, strings.Split(args, " ")...)
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return execCmd.CombinedOutput()
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}
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