118 lines
2.7 KiB
Go
118 lines
2.7 KiB
Go
package shim
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import (
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"context"
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"encoding/gob"
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"errors"
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"os"
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"os/exec"
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"strconv"
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"strings"
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"syscall"
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"time"
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"git.gensokyo.uk/security/fortify/internal"
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"git.gensokyo.uk/security/fortify/internal/fmsg"
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"git.gensokyo.uk/security/fortify/sandbox"
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)
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// used by the parent process
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type Shim struct {
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// user switcher process
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cmd *exec.Cmd
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// fallback exit notifier with error returned killing the process
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killFallback chan error
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// monitor to shim encoder
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encoder *gob.Encoder
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}
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func (s *Shim) Unwrap() *exec.Cmd { return s.cmd }
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func (s *Shim) Fallback() chan error { return s.killFallback }
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func (s *Shim) String() string {
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if s.cmd == nil {
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return "(unused shim manager)"
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}
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return s.cmd.String()
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}
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func (s *Shim) Start(
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aid string,
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supp []string,
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) (*time.Time, error) {
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// prepare user switcher invocation
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fsuPath := internal.MustFsuPath()
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s.cmd = exec.Command(fsuPath)
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// pass shim setup pipe
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if fd, e, err := sandbox.Setup(&s.cmd.ExtraFiles); err != nil {
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return nil, fmsg.WrapErrorSuffix(err,
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"cannot create shim setup pipe:")
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} else {
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s.encoder = e
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s.cmd.Env = []string{
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Env + "=" + strconv.Itoa(fd),
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"FORTIFY_APP_ID=" + aid,
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}
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}
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// format fsu supplementary groups
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if len(supp) > 0 {
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fmsg.Verbosef("attaching supplementary group ids %s", supp)
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s.cmd.Env = append(s.cmd.Env, "FORTIFY_GROUPS="+strings.Join(supp, " "))
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}
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s.cmd.Stdin, s.cmd.Stdout, s.cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
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s.cmd.Dir = "/"
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fmsg.Verbose("starting shim via fsu:", s.cmd)
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// withhold messages to stderr
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fmsg.Suspend()
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if err := s.cmd.Start(); err != nil {
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return nil, fmsg.WrapErrorSuffix(err,
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"cannot start fsu:")
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}
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startTime := time.Now().UTC()
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return &startTime, nil
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}
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func (s *Shim) Serve(ctx context.Context, params *Params) error {
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// kill shim if something goes wrong and an error is returned
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s.killFallback = make(chan error, 1)
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killShim := func() {
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if err := s.cmd.Process.Signal(os.Interrupt); err != nil {
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s.killFallback <- err
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}
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}
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defer func() { killShim() }()
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encodeErr := make(chan error)
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go func() { encodeErr <- s.encoder.Encode(params) }()
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select {
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// encode return indicates setup completion
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case err := <-encodeErr:
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if err != nil {
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return fmsg.WrapErrorSuffix(err,
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"cannot transmit shim config:")
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}
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killShim = func() {}
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return nil
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// setup canceled before payload was accepted
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case <-ctx.Done():
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err := ctx.Err()
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if errors.Is(err, context.Canceled) {
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return fmsg.WrapError(syscall.ECANCELED,
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"shim setup canceled")
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}
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if errors.Is(err, context.DeadlineExceeded) {
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return fmsg.WrapError(syscall.ETIMEDOUT,
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"deadline exceeded waiting for shim")
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}
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// unreachable
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return err
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}
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}
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