test/internal/testsuite: move ptrace helpers

This also cleans up their API.

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

4 files changed, 163 insertions, 4 deletions

diff --git a/test/internal/testsuite/ptrace.go b/test/internal/testsuite/ptrace.go
new file mode 100644
index 00000000..4fcf1508
--- /dev/null
+++ b/test/internal/testsuite/ptrace.go
@@ -0,0 +1,136 @@
+package testsuite
+
+import (
+	"crypto/sha512"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+const (
+	// _PTRACE_ATTACH attaches to the process specified in pid.
+	_PTRACE_ATTACH = 16
+	// _PTRACE_DETACH restarts the stopped tracee as for PTRACE_CONT, but first
+	// detaches from it.
+	_PTRACE_DETACH = 17
+
+	// _PTRACE_SECCOMP_GET_FILTER allows the tracer to dump the tracee's classic
+	// BPF filters.
+	_PTRACE_SECCOMP_GET_FILTER = 0x420c
+)
+
+// ptrace wraps the ptrace syscall.
+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),
+		0, 0,
+	)
+	return
+}
+
+// ptraceAttach attaches to the process referred to by pid.
+func ptraceAttach(pid int) error {
+	if _, errno := ptrace(_PTRACE_ATTACH, pid, 0, nil); errno != 0 {
+		return os.NewSyscallError("PTRACE_ATTACH", errno)
+	}
+
+	var status syscall.WaitStatus
+	for {
+		if _, err := syscall.Wait4(
+			pid,
+			&status,
+			syscall.WALL,
+			nil,
+		); err != nil {
+			if errors.Is(err, syscall.EINTR) {
+				continue
+			}
+			return os.NewSyscallError("wait4", err)
+		}
+		break
+	}
+
+	return nil
+}
+
+// ptraceDetach detaches from the attached process referred to by pid.
+func ptraceDetach(pid int) error {
+	if _, errno := ptrace(_PTRACE_DETACH, pid, 0, nil); errno != 0 {
+		return os.NewSyscallError("PTRACE_DETACH", errno)
+	}
+	return nil
+}
+
+// getFilter dumps the specified tracee's cBPF filter at the specified index
+// and returns the resulting payload. T must be eight bytes long and must not
+// contain pointers.
+func getFilter(pid, index int) ([]syscall.SockFilter, error) {
+	var buf []syscall.SockFilter
+	if n, errno := ptrace(
+		_PTRACE_SECCOMP_GET_FILTER,
+		pid, index, nil,
+	); errno != 0 {
+		return nil, os.NewSyscallError("PTRACE_SECCOMP_GET_FILTER", errno)
+	} else {
+		buf = make([]syscall.SockFilter, n)
+	}
+	if _, errno := ptrace(
+		_PTRACE_SECCOMP_GET_FILTER,
+		pid, index, unsafe.Pointer(&buf[0]),
+	); errno != 0 {
+		return nil, os.NewSyscallError("PTRACE_SECCOMP_GET_FILTER", errno)
+	}
+	return buf, nil
+}
+
+// CheckFilter checks the process at pid to have its first filter's contents
+// match the sha512 checksum specified in hexadecimal string representation.
+func CheckFilter(pid, index int, sum string) (err error) {
+	if err = ptraceAttach(pid); err != nil {
+		return
+	}
+	defer func() {
+		if detachErr := ptraceDetach(pid); err == nil {
+			err = detachErr
+		}
+	}()
+
+	var (
+		buf  []syscall.SockFilter
+		want []byte
+	)
+
+	if want, err = hex.DecodeString(sum); err != nil {
+		return
+	}
+
+	h := sha512.New()
+	if buf, err = getFilter(pid, index); err != nil {
+		return
+	} else {
+		h.Write(unsafe.Slice(
+			(*byte)(unsafe.Pointer(&buf[0])),
+			uintptr(len(buf))*unsafe.Sizeof(buf[0]),
+		))
+	}
+
+	if got := h.Sum(nil); string(got) != string(want) {
+		return fmt.Errorf(
+			"bad filter\n\t got: %s\n\twant: %s",
+			hex.EncodeToString(got),
+			sum,
+		)
+	}
+	return
+}
diff --git a/test/internal/testsuite/ptrace_test.go b/test/internal/testsuite/ptrace_test.go
new file mode 100644
index 00000000..eaaed131
--- /dev/null
+++ b/test/internal/testsuite/ptrace_test.go
@@ -0,0 +1,13 @@
+package testsuite
+
+import (
+	"syscall"
+	"testing"
+	"unsafe"
+)
+
+func TestBlockSize(t *testing.T) {
+	if sz := unsafe.Sizeof(syscall.SockFilter{}); sz != 8 {
+		t.Fatalf("invalid filter block size %d", sz)
+	}
+}
diff --git a/test/internal/testsuite/testsuite.go b/test/internal/testsuite/testsuite.go
index 9233818d..2173509d 100644
--- a/test/internal/testsuite/testsuite.go
+++ b/test/internal/testsuite/testsuite.go
@@ -13,10 +13,6 @@ import (
 func init() {
 	log.SetFlags(0)
 	log.SetPrefix("testsuite: ")
-
-	if os.Geteuid() != 0 {
-		log.Fatal("this program must run as root")
-	}
 }
 
 // ReceiveSignals blocks until a termination signal arrives, and terminates.
diff --git a/test/internal/testsuite/testsuite_root.go b/test/internal/testsuite/testsuite_root.go
new file mode 100644
index 00000000..830e272c
--- /dev/null
+++ b/test/internal/testsuite/testsuite_root.go
@@ -0,0 +1,14 @@
+//go:build testsuite
+
+package testsuite
+
+import (
+	"log"
+	"os"
+)
+
+func init() {
+	if os.Geteuid() != 0 {
+		log.Fatal("this program must run as root")
+	}
+}