container/seccomp: remove export pipe

This was only useful when wrapping bwrap.

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

container/seccomp/hash_test.go

@@ -1,6 +1,7 @@
 package seccomp_test
 
 import (
+	"crypto/sha512"
 	"encoding/hex"
 
 	"hakurei.app/container/bits"
@@ -12,18 +13,18 @@ type (
 		seccomp.ExportFlag
 		bits.FilterPreset
 	}
-	bpfLookup map[bpfPreset][]byte
+	bpfLookup map[bpfPreset][sha512.Size]byte
 )
 
-func toHash(s string) []byte {
-	if len(s) != 128 {
+func toHash(s string) [sha512.Size]byte {
+	if len(s) != sha512.Size*2 {
 		panic("bad sha512 string length")
 	}
 	if v, err := hex.DecodeString(s); err != nil {
 		panic(err.Error())
-	} else if len(v) != 64 {
+	} else if len(v) != sha512.Size {
 		panic("unreachable")
 	} else {
-		return v
+		return ([sha512.Size]byte)(v)
 	}
 }

container/seccomp/libseccomp-helper.c

@@ -9,14 +9,16 @@
 
 #define LEN(arr) (sizeof(arr) / sizeof((arr)[0]))
 
-int32_t hakurei_export_filter(int *ret_p, int fd, uint32_t arch,
-                              uint32_t multiarch,
+int32_t hakurei_scmp_make_filter(int *ret_p, uintptr_t allocate_p,
+                                 uint32_t arch, uint32_t multiarch,
                                  struct hakurei_syscall_rule *rules,
                                  size_t rules_sz, hakurei_export_flag flags) {
   int i;
   int last_allowed_family;
   int disallowed;
   struct hakurei_syscall_rule *rule;
+  void *buf;
+  size_t len = 0;
 
   int32_t res = 0; /* refer to resPrefix for message */
 
@@ -108,14 +110,26 @@ int32_t hakurei_export_filter(int *ret_p, int fd, uint32_t arch,
   seccomp_rule_add_exact(ctx, SCMP_ACT_ERRNO(EAFNOSUPPORT), SCMP_SYS(socket), 1,
                          SCMP_A0(SCMP_CMP_GE, last_allowed_family + 1));
 
-  if (fd < 0) {
+  if (allocate_p == 0) {
     *ret_p = seccomp_load(ctx);
     if (*ret_p != 0) {
       res = 7;
       goto out;
     }
   } else {
-    *ret_p = seccomp_export_bpf(ctx, fd);
+    *ret_p = seccomp_export_bpf_mem(ctx, NULL, &len);
+    if (*ret_p != 0) {
+      res = 6;
+      goto out;
+    }
+
+    buf = hakurei_scmp_allocate(allocate_p, len);
+    if (buf == NULL) {
+      res = 4;
+      goto out;
+    }
+
+    *ret_p = seccomp_export_bpf_mem(ctx, buf, &len);
     if (*ret_p != 0) {
       res = 6;
       goto out;

container/seccomp/libseccomp-helper.h

@@ -18,7 +18,8 @@ struct hakurei_syscall_rule {
   struct scmp_arg_cmp *arg;
 };
 
-int32_t hakurei_export_filter(int *ret_p, int fd, uint32_t arch,
-                              uint32_t multiarch,
+extern void *hakurei_scmp_allocate(uintptr_t f, size_t len);
+int32_t hakurei_scmp_make_filter(int *ret_p, uintptr_t allocate_p,
+                                 uint32_t arch, uint32_t multiarch,
                                  struct hakurei_syscall_rule *rules,
                                  size_t rules_sz, hakurei_export_flag flags);

container/seccomp/libseccomp.go

@@ -3,7 +3,7 @@ package seccomp
 /*
 #cgo linux pkg-config: --static libseccomp
 
-#include <libseccomp-helper.h>
+#include "libseccomp-helper.h"
 #include <sys/personality.h>
 */
 import "C"
@@ -11,23 +11,21 @@ import (
 	"errors"
 	"fmt"
 	"runtime"
+	"runtime/cgo"
 	"syscall"
 	"unsafe"
 )
 
-const (
-	PER_LINUX   = C.PER_LINUX
-	PER_LINUX32 = C.PER_LINUX32
-)
-
-var (
-	ErrInvalidRules = errors.New("invalid native rules slice")
-)
+// ErrInvalidRules is returned for a zero-length rules slice.
+var ErrInvalidRules = errors.New("invalid native rules slice")
 
 // LibraryError represents a libseccomp error.
 type LibraryError struct {
+	// User facing description of the libseccomp function returning the error.
 	Prefix string
+	// Negated errno value returned by libseccomp.
 	Seccomp syscall.Errno
+	// Global errno value on return.
 	Errno error
 }
 
@@ -56,7 +54,9 @@ func (e *LibraryError) Is(err error) bool {
 }
 
 type (
+	// ScmpSyscall represents a syscall number passed to libseccomp via [NativeRule.Syscall].
 	ScmpSyscall = C.int
+	// ScmpErrno represents an errno value passed to libseccomp via [NativeRule.Errno].
 	ScmpErrno = C.int
 )
 
@@ -88,12 +88,23 @@ var resPrefix = [...]string{
 	3: "seccomp_arch_add failed (multiarch)",
 	4: "internal libseccomp failure",
 	5: "seccomp_rule_add failed",
-	6: "seccomp_export_bpf failed",
+	6: "seccomp_export_bpf_mem failed",
 	7: "seccomp_load failed",
 }
 
-// Export streams filter contents to fd, or installs it to the current process if fd < 0.
-func Export(fd int, rules []NativeRule, flags ExportFlag) error {
+// cbAllocateBuffer is the function signature for the function handle passed to hakurei_export_filter
+// which allocates the buffer that the resulting bpf program is copied into, and writes its slice header
+// to a value held by the caller.
+type cbAllocateBuffer = func(len C.size_t) (buf unsafe.Pointer)
+
+//export hakurei_scmp_allocate
+func hakurei_scmp_allocate(f C.uintptr_t, len C.size_t) (buf unsafe.Pointer) {
+	return cgo.Handle(f).Value().(cbAllocateBuffer)(len)
+}
+
+// makeFilter generates a bpf program from a slice of [NativeRule] and writes the resulting byte slice to p.
+// The filter is installed to the current process if p is nil.
+func makeFilter(rules []NativeRule, flags ExportFlag, p *[]byte) error {
 	if len(rules) == 0 {
 		return ErrInvalidRules
 	}
@@ -117,33 +128,56 @@ func Export(fd int, rules []NativeRule, flags ExportFlag) error {
 
 	var ret C.int
 
-	var rulesPinner runtime.Pinner
+	var scmpPinner runtime.Pinner
 	for i := range rules {
 		rule := &rules[i]
-		rulesPinner.Pin(rule)
+		scmpPinner.Pin(rule)
 		if rule.Arg != nil {
-			rulesPinner.Pin(rule.Arg)
+			scmpPinner.Pin(rule.Arg)
 		}
 	}
-	res, err := C.hakurei_export_filter(
-		&ret, C.int(fd),
+
+	var allocateP cgo.Handle
+	if p != nil {
+		allocateP = cgo.NewHandle(func(len C.size_t) (buf unsafe.Pointer) {
+			// this is so the slice header gets a Go pointer
+			*p = make([]byte, len)
+
+			buf = unsafe.Pointer(unsafe.SliceData(*p))
+			scmpPinner.Pin(buf)
+			return
+		})
+	}
+
+	res, err := C.hakurei_scmp_make_filter(
+		&ret, C.uintptr_t(allocateP),
 		arch, multiarch,
 		(*C.struct_hakurei_syscall_rule)(unsafe.Pointer(&rules[0])),
 		C.size_t(len(rules)),
 		flags,
 	)
-	rulesPinner.Unpin()
+	scmpPinner.Unpin()
+	if p != nil {
+		allocateP.Delete()
+	}
 
 	if prefix := resPrefix[res]; prefix != "" {
-		return &LibraryError{
-			prefix,
-			-syscall.Errno(ret),
-			err,
-		}
+		return &LibraryError{prefix, syscall.Errno(-ret), err}
 	}
 	return err
 }
 
+// Export generates a bpf program from a slice of [NativeRule].
+// Errors returned by libseccomp is wrapped in [LibraryError].
+func Export(rules []NativeRule, flags ExportFlag) (data []byte, err error) {
+	err = makeFilter(rules, flags, &data)
+	return
+}
+
+// Load generates a bpf program from a slice of [NativeRule] and enforces it on the current process.
+// Errors returned by libseccomp is wrapped in [LibraryError].
+func Load(rules []NativeRule, flags ExportFlag) error { return makeFilter(rules, flags, nil) }
+
 // ScmpCompare is the equivalent of scmp_compare;
 // Comparison operators
 type ScmpCompare = C.enum_scmp_compare
@@ -184,7 +218,15 @@ type ScmpArgCmp struct {
 	DatumA, DatumB ScmpDatum
 }
 
-// only used for testing
+const (
+	// PersonaLinux is passed in a [ScmpDatum] for filtering calls to syscall.SYS_PERSONALITY.
+	PersonaLinux = C.PER_LINUX
+	// PersonaLinux32 is passed in a [ScmpDatum] for filtering calls to syscall.SYS_PERSONALITY.
+	PersonaLinux32 = C.PER_LINUX32
+)
+
+// syscallResolveName resolves a syscall number by name via seccomp_syscall_resolve_name.
+// This function is only for testing the lookup tables and included here for convenience.
 func syscallResolveName(s string) (trap int) {
 	v := C.CString(s)
 	trap = int(C.seccomp_syscall_resolve_name(v))

container/seccomp/libseccomp_test.go

@@ -3,8 +3,6 @@ package seccomp_test
 import (
 	"crypto/sha512"
 	"errors"
-	"io"
-	"slices"
 	"syscall"
 	"testing"
 
@@ -12,6 +10,67 @@ import (
 	. "hakurei.app/container/seccomp"
 )
 
+func TestLibraryError(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name    string
+		sample  *LibraryError
+		want    string
+		wantIs  bool
+		compare error
+	}{
+		{
+			"full",
+			&LibraryError{Prefix: "seccomp_export_bpf failed", Seccomp: syscall.ECANCELED, Errno: syscall.EBADF},
+			"seccomp_export_bpf failed: operation canceled (bad file descriptor)",
+			true,
+			&LibraryError{Prefix: "seccomp_export_bpf failed", Seccomp: syscall.ECANCELED, Errno: syscall.EBADF},
+		},
+		{
+			"errno only",
+			&LibraryError{Prefix: "seccomp_init failed", Errno: syscall.ENOMEM},
+			"seccomp_init failed: cannot allocate memory",
+			false,
+			nil,
+		},
+		{
+			"seccomp only",
+			&LibraryError{Prefix: "internal libseccomp failure", Seccomp: syscall.EFAULT},
+			"internal libseccomp failure: bad address",
+			true,
+			syscall.EFAULT,
+		},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			if errors.Is(tc.sample, tc.compare) != tc.wantIs {
+				t.Errorf("errors.Is(%#v, %#v) did not return %v",
+					tc.sample, tc.compare, tc.wantIs)
+			}
+
+			if got := tc.sample.Error(); got != tc.want {
+				t.Errorf("Error: %q, want %q",
+					got, tc.want)
+			}
+		})
+	}
+
+	t.Run("invalid", func(t *testing.T) {
+		t.Parallel()
+
+		wantPanic := "invalid libseccomp error"
+		defer func() {
+			if r := recover(); r != wantPanic {
+				t.Errorf("panic: %q, want %q", r, wantPanic)
+			}
+		}()
+		_ = new(LibraryError).Error()
+	})
+}
+
 func TestExport(t *testing.T) {
 	t.Parallel()
 
@@ -38,61 +97,34 @@ func TestExport(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			e := New(Preset(tc.presets, tc.flags), tc.flags)
 			want := bpfExpected[bpfPreset{tc.flags, tc.presets}]
-			digest := sha512.New()
-
-			if _, err := io.Copy(digest, e); (err != nil) != tc.wantErr {
-				t.Errorf("Exporter: error = %v, wantErr %v", err, tc.wantErr)
+			if data, err := Export(Preset(tc.presets, tc.flags), tc.flags); (err != nil) != tc.wantErr {
+				t.Errorf("Export: error = %v, wantErr %v", err, tc.wantErr)
 				return
-			}
-			if err := e.Close(); err != nil {
-				t.Errorf("Close: error = %v", err)
-			}
-			if got := digest.Sum(nil); !slices.Equal(got, want) {
-				t.Fatalf("Export: hash = %x, want %x",
-					got, want)
+			} else if got := sha512.Sum512(data); got != want {
+				t.Fatalf("Export: hash = %x, want %x", got, want)
 				return
 			}
 		})
 	}
-
-	t.Run("close without use", func(t *testing.T) {
-		e := New(Preset(0, 0), 0)
-		if err := e.Close(); !errors.Is(err, syscall.EINVAL) {
-			t.Errorf("Close: error = %v", err)
-			return
-		}
-	})
-
-	t.Run("close partial read", func(t *testing.T) {
-		e := New(Preset(0, 0), 0)
-		if _, err := e.Read(nil); err != nil {
-			t.Errorf("Read: error = %v", err)
-			return
-		}
-		// the underlying implementation uses buffered io, so the outcome of this is nondeterministic;
-		// that is not harmful however, so both outcomes are checked for here
-		if err := e.Close(); err != nil &&
-			(!errors.Is(err, syscall.ECANCELED) || !errors.Is(err, syscall.EBADF)) {
-			t.Errorf("Close: error = %v", err)
-			return
-		}
-	})
 }
 
 func BenchmarkExport(b *testing.B) {
-	buf := make([]byte, 8)
+	const exportFlags = AllowMultiarch | AllowCAN | AllowBluetooth
+	const presetFlags = PresetExt | PresetDenyNS | PresetDenyTTY | PresetDenyDevel | PresetLinux32
+	var want = bpfExpected[bpfPreset{exportFlags, presetFlags}]
+
 	for b.Loop() {
-		e := New(
-			Preset(PresetExt|PresetDenyNS|PresetDenyTTY|PresetDenyDevel|PresetLinux32,
-				AllowMultiarch|AllowCAN|AllowBluetooth),
-			AllowMultiarch|AllowCAN|AllowBluetooth)
-		if _, err := io.CopyBuffer(io.Discard, e, buf); err != nil {
-			b.Fatalf("cannot export: %v", err)
+		data, err := Export(Preset(presetFlags, exportFlags), exportFlags)
+
+		b.StopTimer()
+		if err != nil {
+			b.Fatalf("Export: error = %v", err)
 		}
-		if err := e.Close(); err != nil {
-			b.Fatalf("cannot close exporter: %v", err)
+		if got := sha512.Sum512(data); got != want {
+			b.Fatalf("Export: hash = %x, want %x", got, want)
+			return
 		}
+		b.StartTimer()
 	}
 }

container/seccomp/presets.go

@@ -9,9 +9,9 @@ import (
 )
 
 func Preset(presets bits.FilterPreset, flags ExportFlag) (rules []NativeRule) {
-	allowedPersonality := PER_LINUX
+	allowedPersonality := PersonaLinux
 	if presets&bits.PresetLinux32 != 0 {
-		allowedPersonality = PER_LINUX32
+		allowedPersonality = PersonaLinux32
 	}
 	presetDevelFinal := presetDevel(ScmpDatum(allowedPersonality))
 

container/seccomp/proc.go

@@ -1,72 +0,0 @@
-package seccomp
-
-import (
-	"context"
-	"errors"
-	"syscall"
-
-	"hakurei.app/helper/proc"
-)
-
-// New returns an inactive Encoder instance.
-func New(rules []NativeRule, flags ExportFlag) *Encoder { return &Encoder{newExporter(rules, flags)} }
-
-// Load loads a filter into the kernel.
-func Load(rules []NativeRule, flags ExportFlag) error { return Export(-1, rules, flags) }
-
-/*
-An Encoder writes a BPF program to an output stream.
-
-Methods of Encoder are not safe for concurrent use.
-
-An Encoder must not be copied after first use.
-*/
-type Encoder struct{ *exporter }
-
-func (e *Encoder) Read(p []byte) (n int, err error) {
-	if err = e.prepare(); err != nil {
-		return
-	}
-	return e.r.Read(p)
-}
-
-func (e *Encoder) Close() error {
-	if e.r == nil {
-		return syscall.EINVAL
-	}
-
-	// this hangs if the cgo thread fails to exit
-	return errors.Join(e.closeWrite(), <-e.exportErr)
-}
-
-// NewFile returns an instance of exporter implementing [proc.File].
-func NewFile(rules []NativeRule, flags ExportFlag) proc.File {
-	return &File{rules: rules, flags: flags}
-}
-
-// File implements [proc.File] and provides access to the read end of exporter pipe.
-type File struct {
-	rules []NativeRule
-	flags ExportFlag
-	proc.BaseFile
-}
-
-func (f *File) ErrCount() int { return 2 }
-func (f *File) Fulfill(ctx context.Context, dispatchErr func(error)) error {
-	e := newExporter(f.rules, f.flags)
-	if err := e.prepare(); err != nil {
-		return err
-	}
-	f.Set(e.r)
-	go func() {
-		select {
-		case err := <-e.exportErr:
-			dispatchErr(nil)
-			dispatchErr(err)
-		case <-ctx.Done():
-			dispatchErr(e.closeWrite())
-			dispatchErr(<-e.exportErr)
-		}
-	}()
-	return nil
-}

container/seccomp/seccomp.go

@@ -1,60 +0,0 @@
-// Package seccomp provides high level wrappers around libseccomp.
-package seccomp
-
-import (
-	"os"
-	"runtime"
-	"sync"
-)
-
-type exporter struct {
-	rules []NativeRule
-	flags ExportFlag
-	r, w  *os.File
-
-	prepareOnce sync.Once
-	prepareErr  error
-	closeOnce   sync.Once
-	closeErr    error
-	exportErr   <-chan error
-}
-
-func (e *exporter) prepare() error {
-	e.prepareOnce.Do(func() {
-		if r, w, err := os.Pipe(); err != nil {
-			e.prepareErr = err
-			return
-		} else {
-			e.r, e.w = r, w
-		}
-
-		ec := make(chan error, 1)
-		go func(fd uintptr) {
-			ec <- Export(int(fd), e.rules, e.flags)
-			close(ec)
-			_ = e.closeWrite()
-			runtime.KeepAlive(e.w)
-		}(e.w.Fd())
-		e.exportErr = ec
-		runtime.SetFinalizer(e, (*exporter).closeWrite)
-	})
-	return e.prepareErr
-}
-
-func (e *exporter) closeWrite() error {
-	e.closeOnce.Do(func() {
-		if e.w == nil {
-			panic("closeWrite called on invalid exporter")
-		}
-		e.closeErr = e.w.Close()
-
-		// no need for a finalizer anymore
-		runtime.SetFinalizer(e, nil)
-	})
-
-	return e.closeErr
-}
-
-func newExporter(rules []NativeRule, flags ExportFlag) *exporter {
-	return &exporter{rules: rules, flags: flags}
-}

container/seccomp/seccomp_test.go

@@ -1,71 +0,0 @@
-package seccomp_test
-
-import (
-	"errors"
-	"runtime"
-	"syscall"
-	"testing"
-
-	"hakurei.app/container/seccomp"
-)
-
-func TestLibraryError(t *testing.T) {
-	t.Parallel()
-
-	testCases := []struct {
-		name    string
-		sample  *seccomp.LibraryError
-		want    string
-		wantIs  bool
-		compare error
-	}{
-		{
-			"full",
-			&seccomp.LibraryError{Prefix: "seccomp_export_bpf failed", Seccomp: syscall.ECANCELED, Errno: syscall.EBADF},
-			"seccomp_export_bpf failed: operation canceled (bad file descriptor)",
-			true,
-			&seccomp.LibraryError{Prefix: "seccomp_export_bpf failed", Seccomp: syscall.ECANCELED, Errno: syscall.EBADF},
-		},
-		{
-			"errno only",
-			&seccomp.LibraryError{Prefix: "seccomp_init failed", Errno: syscall.ENOMEM},
-			"seccomp_init failed: cannot allocate memory",
-			false,
-			nil,
-		},
-		{
-			"seccomp only",
-			&seccomp.LibraryError{Prefix: "internal libseccomp failure", Seccomp: syscall.EFAULT},
-			"internal libseccomp failure: bad address",
-			true,
-			syscall.EFAULT,
-		},
-	}
-	for _, tc := range testCases {
-		t.Run(tc.name, func(t *testing.T) {
-			t.Parallel()
-
-			if errors.Is(tc.sample, tc.compare) != tc.wantIs {
-				t.Errorf("errors.Is(%#v, %#v) did not return %v",
-					tc.sample, tc.compare, tc.wantIs)
-			}
-
-			if got := tc.sample.Error(); got != tc.want {
-				t.Errorf("Error: %q, want %q",
-					got, tc.want)
-			}
-		})
-	}
-
-	t.Run("invalid", func(t *testing.T) {
-		t.Parallel()
-
-		wantPanic := "invalid libseccomp error"
-		defer func() {
-			if r := recover(); r != wantPanic {
-				t.Errorf("panic: %q, want %q", r, wantPanic)
-			}
-		}()
-		runtime.KeepAlive(new(seccomp.LibraryError).Error())
-	})
-}