test/sandbox/ptrace: dump seccomp bpf program

Signed-off-by: Ophestra <cat@gensokyo.uk>

test/sandbox/ptrace.go

@@ -0,0 +1,115 @@
+package sandbox
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+	"syscall"
+	"time"
+	"unsafe"
+)
+
+const (
+	NULL = 0
+
+	PTRACE_ATTACH             = 16
+	PTRACE_DETACH             = 17
+	PTRACE_SECCOMP_GET_FILTER = 0x420c
+)
+
+type ptraceError struct {
+	op    string
+	errno syscall.Errno
+}
+
+func (p *ptraceError) Error() string { return fmt.Sprintf("%s: %v", p.op, p.errno) }
+
+func (p *ptraceError) Unwrap() error {
+	if p.errno == 0 {
+		return nil
+	}
+	return p.errno
+}
+
+func ptrace(op uintptr, pid, addr int, data unsafe.Pointer) (r uintptr, errno syscall.Errno) {
+	r, _, errno = syscall.Syscall6(syscall.SYS_PTRACE, op, uintptr(pid), uintptr(addr), uintptr(data), NULL, NULL)
+	return
+}
+
+func ptraceAttach(pid int) error {
+	const (
+		statePrefix = "State:"
+		stateSuffix = "t (tracing stop)"
+	)
+
+	var r io.ReadSeekCloser
+	if f, err := os.Open(fmt.Sprintf("/proc/%d/status", pid)); err != nil {
+		return err
+	} else {
+		r = f
+	}
+
+	if _, errno := ptrace(PTRACE_ATTACH, pid, 0, nil); errno != 0 {
+		return &ptraceError{"PTRACE_ATTACH", errno}
+	}
+
+	// ugly! but there does not appear to be another way
+	for {
+		time.Sleep(10 * time.Millisecond)
+
+		if _, err := r.Seek(0, io.SeekStart); err != nil {
+			return err
+		}
+		s := bufio.NewScanner(r)
+
+		var found bool
+		for s.Scan() {
+			found = strings.HasPrefix(s.Text(), statePrefix)
+			if found {
+				break
+			}
+		}
+		if err := s.Err(); err != nil {
+			return err
+		}
+
+		if !found {
+			return syscall.EBADE
+		}
+
+		if strings.HasSuffix(s.Text(), stateSuffix) {
+			break
+		}
+	}
+
+	return nil
+}
+
+func ptraceDetach(pid int) error {
+	if _, errno := ptrace(PTRACE_DETACH, pid, 0, nil); errno != 0 {
+		return &ptraceError{"PTRACE_DETACH", errno}
+	}
+	return nil
+}
+
+type sockFilter struct { /* Filter block */
+	code uint16 /* Actual filter code */
+	jt   uint8  /* Jump true */
+	jf   uint8  /* Jump false */
+	k    uint32 /* Generic multiuse field */
+}
+
+func getFilter(pid, index int) ([]sockFilter, error) {
+	var buf []sockFilter
+	if n, errno := ptrace(PTRACE_SECCOMP_GET_FILTER, pid, index, nil); errno != 0 {
+		return nil, &ptraceError{"PTRACE_SECCOMP_GET_FILTER", errno}
+	} else {
+		buf = make([]sockFilter, n)
+	}
+	if _, errno := ptrace(PTRACE_SECCOMP_GET_FILTER, pid, index, unsafe.Pointer(&buf[0])); errno != 0 {
+		return nil, &ptraceError{"PTRACE_SECCOMP_GET_FILTER", errno}
+	}
+	return buf, nil
+}