package idtools // import "github.com/docker/docker/pkg/idtools" import ( "fmt" "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 // useradd -r -s /bin/false 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" ) // 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 }