gopathrs: return raw errors from openat2 retry loop

This is to match the new behavour from libpathrs, as it provides more
reasonable information to downstream users (they can check for
unix.EAGAIN and have their own custom retry logic).

Ref: cyphar/libpathrs#265
Signed-off-by: Aleksa Sarai <[email protected]>

Author: cyphar

pathrs-lite/internal/fd/openat2_linux.go

@@ -17,8 +17,6 @@ import (
 	"runtime"
 
 	"golang.org/x/sys/unix"
-
-	"github.com/cyphar/filepath-securejoin/pathrs-lite/internal"
 )
 
 func scopedLookupShouldRetry(how *unix.OpenHow, err error) bool {
@@ -43,10 +41,10 @@ func Openat2(dir Fd, path string, how *unix.OpenHow) (*os.File, error) {
 	// Make sure we always set O_CLOEXEC.
 	how.Flags |= unix.O_CLOEXEC
 	var tries int
-	for tries < scopedLookupMaxRetries {
+	for {
 		fd, err := unix.Openat2(dirFd, path, how)
 		if err != nil {
-			if scopedLookupShouldRetry(how, err) {
+			if scopedLookupShouldRetry(how, err) && tries < scopedLookupMaxRetries {
 				// We retry a couple of times to avoid the spurious errors, and
 				// if we are being attacked then returning -EAGAIN is the best
 				// we can do.
@@ -58,5 +56,4 @@ func Openat2(dir Fd, path string, how *unix.OpenHow) (*os.File, error) {
 		runtime.KeepAlive(dir)
 		return os.NewFile(uintptr(fd), fullPath), nil
 	}
-	return nil, &os.PathError{Op: "openat2", Path: fullPath, Err: internal.ErrPossibleAttack}
 }

pathrs-lite/internal/gopathrs/lookup_linux_test.go

@@ -24,7 +24,6 @@ import (
 	"github.com/stretchr/testify/require"
 	"golang.org/x/sys/unix"
 
-	"github.com/cyphar/filepath-securejoin/pathrs-lite/internal"
 	"github.com/cyphar/filepath-securejoin/pathrs-lite/internal/fd"
 	"github.com/cyphar/filepath-securejoin/pathrs-lite/internal/gocompat"
 	"github.com/cyphar/filepath-securejoin/pathrs-lite/internal/procfs"
@@ -580,7 +579,7 @@ func TestPartialLookup_RacingRename(t *testing.T) {
 			)},
 		} {
 			test := test // copy iterator
-			test.skipErrs = append(test.skipErrs, internal.ErrPossibleAttack, internal.ErrPossibleBreakout)
+			test.skipErrs = append(test.skipErrs, unix.EAGAIN, unix.EXDEV)
 			t.Run(name, func(t *testing.T) {
 				root := testutils.CreateTree(t, tree...)