Add ENAMETOOLONG checks in overlayfs.

Linux overlayfs uses the max of all layers' filename length limit. Do the same
in gVisor.

This is needed to get PHP runtime test ext/standard/tests/strings/007.phpt to
pass with overlayfs.

PiperOrigin-RevId: 493942515

Makefile

@@ -270,6 +270,7 @@ docker-tests: load-basic $(RUNTIME_BIN)
 	@$(call install_runtime,$(RUNTIME)-fdlimit,--fdlimit=2000) # Used by TestRlimitNoFile.
 	@$(call install_runtime,$(RUNTIME)-dcache,--fdlimit=2000 --dcache=100) # Used by TestDentryCacheLimit.
 	@$(call install_runtime,$(RUNTIME)-host-uds,--host-uds=all) # Used by TestHostSocketConnect.
+	@$(call install_runtime,$(RUNTIME)-overlay,--overlay2=root:/tmp) # Used by TestOverlay*.
 	@$(call test_runtime,$(RUNTIME),$(INTEGRATION_TARGETS) //test/e2e:integration_runtime_test)
 .PHONY: docker-tests
 

pkg/sentry/fsimpl/overlay/filesystem.go

@@ -161,6 +161,9 @@ afterSymlink:
 		rp.Advance()
 		return d.parent, d.parent.topLookupLayer(), nil
 	}
+	if uint64(len(name)) > fs.maxFilenameLen {
+		return nil, lookupLayerNone, linuxerr.ENAMETOOLONG
+	}
 	child, topLookupLayer, err := fs.getChildLocked(ctx, d, name, ds)
 	if err != nil {
 		return nil, topLookupLayer, err
@@ -504,6 +507,9 @@ func (fs *filesystem) doCreateAt(ctx context.Context, rp *vfs.ResolvingPath, ct
 	if name == "." || name == ".." {
 		return linuxerr.EEXIST
 	}
+	if uint64(len(name)) > fs.maxFilenameLen {
+		return linuxerr.ENAMETOOLONG
+	}
 	if parent.vfsd.IsDead() {
 		return linuxerr.ENOENT
 	}
@@ -1090,6 +1096,9 @@ func (fs *filesystem) RenameAt(ctx context.Context, rp *vfs.ResolvingPath, oldPa
 		}
 		return linuxerr.EBUSY
 	}
+	if uint64(len(newName)) > fs.maxFilenameLen {
+		return linuxerr.ENAMETOOLONG
+	}
 	// Do not check for newName length, since different filesystem
 	// implementations impose different name limits. upperfs.RenameAt() will fail
 	// appropriately if it has to.

pkg/sentry/fsimpl/overlay/overlay.go

@@ -125,6 +125,9 @@ type filesystem struct {
 	// lastDirIno is the last inode number assigned to a directory. lastDirIno
 	// is protected by dirInoCacheMu.
 	lastDirIno uint64
+
+	// MaxFilenameLen is the maximum filename length allowed by the overlayfs.
+	maxFilenameLen uint64
 }
 
 // +stateify savable
@@ -264,9 +267,23 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 		dirDevMinor:    dirDevMinor,
 		lowerDevMinors: make(map[layerDevNumber]uint32),
 		dirInoCache:    make(map[layerDevNoAndIno]uint64),
+		maxFilenameLen: linux.NAME_MAX,
 	}
 	fs.vfsfs.Init(vfsObj, &fstype, fs)
 
+	// Configure max filename length. Similar to what Linux does in
+	// fs/overlayfs/super.c:ovl_fill_super() -> ... -> ovl_check_namelen().
+	if fsopts.UpperRoot.Ok() {
+		if err := fs.updateMaxNameLen(ctx, creds, vfsObj, fs.opts.UpperRoot); err != nil {
+			ctx.Debugf("overlay.FilesystemType.GetFilesystem: failed to StatFSAt on upper layer root: %v", err)
+		}
+	}
+	for _, lowerRoot := range fsopts.LowerRoots {
+		if err := fs.updateMaxNameLen(ctx, creds, vfsObj, lowerRoot); err != nil {
+			ctx.Debugf("overlay.FilesystemType.GetFilesystem: failed to StatFSAt on lower layer root: %v", err)
+		}
+	}
+
 	// Construct the root dentry.
 	root := fs.newDentry()
 	root.refs = atomicbitops.FromInt64(1)
@@ -368,6 +385,21 @@ func (fs *filesystem) Release(ctx context.Context) {
 	}
 }
 
+// updateMaxNameLen is analogous to fs/overlayfs/super.c:ovl_check_namelen().
+func (fs *filesystem) updateMaxNameLen(ctx context.Context, creds *auth.Credentials, vfsObj *vfs.VirtualFilesystem, vd vfs.VirtualDentry) error {
+	statfs, err := vfsObj.StatFSAt(ctx, creds, &vfs.PathOperation{
+		Root:  vd,
+		Start: vd,
+	})
+	if err != nil {
+		return err
+	}
+	if statfs.NameLength > fs.maxFilenameLen {
+		fs.maxFilenameLen = statfs.NameLength
+	}
+	return nil
+}
+
 func (fs *filesystem) statFS(ctx context.Context) (linux.Statfs, error) {
 	// Always statfs the root of the topmost layer. Compare Linux's
 	// fs/overlayfs/super.c:ovl_statfs().

test/e2e/integration_runtime_test.go

@@ -24,6 +24,7 @@ package integration
 import (
 	"context"
 	"flag"
+	"fmt"
 	"io/ioutil"
 	"net"
 	"os"
@@ -178,3 +179,20 @@ func TestHostSocketConnect(t *testing.T) {
 	}
 	wg.Wait()
 }
+
+func TestOverlayNameTooLong(t *testing.T) {
+	ctx := context.Background()
+	d := dockerutil.MakeContainerWithRuntime(ctx, t, "-overlay")
+	defer d.CleanUp(ctx)
+
+	opts := dockerutil.RunOpts{
+		Image:   "basic/integrationtest",
+		WorkDir: "/root",
+	}
+	longName := strings.Repeat("a", unix.NAME_MAX+1)
+	if got, err := d.Run(ctx, opts, "bash", "-c", fmt.Sprintf("stat %s || true", longName)); err != nil {
+		t.Fatalf("docker run failed: %v", err)
+	} else if want := "File name too long"; !strings.Contains(got, want) {
+		t.Errorf("container output %q does not contain %q", got, want)
+	}
+}