fusefrontend: make Access() symlink-safe.

Make Access() symlink-safe through use of faccessat.

2 files changed, 36 insertions, 5 deletions

diff --git a/internal/fusefrontend/fs.go b/internal/fusefrontend/fs.go
index c0d6151..d2f4867 100644
--- a/internal/fusefrontend/fs.go
+++ b/internal/fusefrontend/fs.go
@@ -581,16 +581,20 @@ func (fs *FS) Link(oldPath string, newPath string, context *fuse.Context) (code
 	return fuse.ToStatus(err)
 }
 
-// Access implements pathfs.Filesystem.
-func (fs *FS) Access(path string, mode uint32, context *fuse.Context) (code fuse.Status) {
-	if fs.isFiltered(path) {
+// Access - FUSE call. Check if a file can be accessed in the specified mode(s)
+// (read, write, execute).
+//
+// Symlink-safe through use of faccessat.
+func (fs *FS) Access(relPath string, mode uint32, context *fuse.Context) (code fuse.Status) {
+	if fs.isFiltered(relPath) {
 		return fuse.EPERM
 	}
-	cPath, err := fs.getBackingPath(path)
+	dirfd, cName, err := fs.openBackingDir(relPath)
 	if err != nil {
 		return fuse.ToStatus(err)
 	}
-	return fuse.ToStatus(syscall.Access(cPath, mode))
+	err = unix.Faccessat(dirfd, cName, mode, unix.AT_SYMLINK_NOFOLLOW)
+	return fuse.ToStatus(err)
 }
 
 // reportMitigatedCorruption is used to report a corruption that was transparently
diff --git a/tests/matrix/matrix_test.go b/tests/matrix/matrix_test.go
index 6ec41bd..8de835f 100644
--- a/tests/matrix/matrix_test.go
+++ b/tests/matrix/matrix_test.go
@@ -23,6 +23,8 @@ import (
 	"syscall"
 	"testing"
 
+	"golang.org/x/sys/unix"
+
 	"github.com/rfjakob/gocryptfs/internal/stupidgcm"
 	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
 	"github.com/rfjakob/gocryptfs/tests/test_helpers"
@@ -915,3 +917,28 @@ func TestChmod(t *testing.T) {
 		}
 	}
 }
+
+// Test that access(2) works correctly
+func TestAccess(t *testing.T) {
+	// Note: t.Name() is not available before in Go 1.8
+	tName := "TestAccess"
+	path := test_helpers.DefaultPlainDir + "/" + tName
+	file, err := os.Create(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer file.Close()
+
+	err = unix.Access(path, unix.F_OK)
+	if err != nil {
+		t.Error(err)
+	}
+	err = unix.Access(path, unix.R_OK)
+	if err != nil {
+		t.Error(err)
+	}
+	err = unix.Access(path, unix.X_OK)
+	if err == nil {
+		t.Error("X_OK should have failed")
+	}
+}