116 lines
3.7 KiB
Go
116 lines
3.7 KiB
Go
package sysadm
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import (
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"fmt"
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"os"
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"os/user"
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"path/filepath"
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"strconv"
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"strings"
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"ssh-access-tui/internal/model"
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)
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// managedMarker delimits the block we own inside authorized_keys, so the
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// file can in principle carry other content without us clobbering it.
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const managedMarker = "# ssh-access-tui managed key — do not edit by hand, use the TUI"
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// BuildKeyOptions renders the authorized_keys option string that is the
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// actual security boundary for a jump/forward-only account:
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// - restrict disables pty, X11, agent-forwarding, user-rc, etc.
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// - port-forwarding re-enables (only) local/dynamic forwarding
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// - permitopen=... whitelists exactly the address:port pairs this key
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// may forward to — this is what makes "only these destinations" a
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// protocol-level guarantee rather than a client-side convention. Every
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// service on every host the user's groups grant becomes one
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// permitopen= entry here, independent of how many services share a
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// host or how many hosts share a port number.
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//
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// Reverse forwarding (-R) is intentionally never granted here.
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func BuildKeyOptions(forwards []model.Forward) string {
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if len(forwards) == 0 {
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// No forwards assigned yet: restrict everything, permit nothing, so
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// the key authenticates but cannot open forwarding channels anywhere.
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return "restrict"
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}
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opts := []string{"restrict", "port-forwarding"}
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for _, f := range forwards {
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opts = append(opts, fmt.Sprintf(`permitopen="%s:%s"`, f.Address, strconv.Itoa(f.Port)))
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}
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return strings.Join(opts, ",")
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}
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// WriteAuthorizedKeys writes the single managed key line (with its
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// permitopen restrictions) into ~<username>/.ssh/authorized_keys, replacing
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// any previous ssh-access-tui-managed line for that user.
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func WriteAuthorizedKeys(username, pubKeyLine string, forwards []model.Forward) error {
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u, err := user.Lookup(username)
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if err != nil {
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return fmt.Errorf("lookup user %s: %w", username, err)
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}
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sshDir := filepath.Join(u.HomeDir, ".ssh")
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if err := os.MkdirAll(sshDir, 0o700); err != nil {
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return fmt.Errorf("create .ssh dir: %w", err)
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}
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line := fmt.Sprintf("%s %s", BuildKeyOptions(forwards), strings.TrimSpace(pubKeyLine))
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content := managedMarker + "\n" + line + "\n"
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akPath := filepath.Join(sshDir, "authorized_keys")
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if err := os.WriteFile(akPath, []byte(content), 0o600); err != nil {
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return fmt.Errorf("write authorized_keys: %w", err)
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}
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if err := chownRecursive(sshDir, u); err != nil {
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return fmt.Errorf("chown .ssh dir: %w", err)
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}
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return nil
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}
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// DisableAuthorizedKeys comments out the managed key so the account cannot
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// authenticate at all, without deleting the record of what the key was
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// (useful when re-enabling a returning employee later).
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func DisableAuthorizedKeys(username string) error {
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u, err := user.Lookup(username)
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if err != nil {
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return fmt.Errorf("lookup user %s: %w", username, err)
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}
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akPath := filepath.Join(u.HomeDir, ".ssh", "authorized_keys")
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data, err := os.ReadFile(akPath)
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if os.IsNotExist(err) {
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return nil
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}
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if err != nil {
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return fmt.Errorf("read authorized_keys: %w", err)
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}
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lines := strings.Split(string(data), "\n")
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for i, l := range lines {
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if strings.HasPrefix(l, "restrict") {
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lines[i] = "# LOCKED: " + l
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}
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}
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return os.WriteFile(akPath, []byte(strings.Join(lines, "\n")), 0o600)
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}
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func chownRecursive(dir string, u *user.User) error {
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uid, err := strconv.Atoi(u.Uid)
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if err != nil {
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return err
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}
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gid, err := strconv.Atoi(u.Gid)
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if err != nil {
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return err
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}
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if err := os.Chown(dir, uid, gid); err != nil {
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return err
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}
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entries, err := os.ReadDir(dir)
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if err != nil {
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return err
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}
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for _, e := range entries {
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if err := os.Chown(filepath.Join(dir, e.Name()), uid, gid); err != nil {
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return err
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}
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}
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return nil
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}
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