From 8c975e6e6e68fefde64f68bdbebc41aafb0f9fcb Mon Sep 17 00:00:00 2001
From: Nicolas Lacasse <nlacasse@google.com>
Date: Thu, 8 Jun 2023 10:22:10 -0700
Subject: [PATCH] Mark some kernfs inode as Anonymous.

These inodes can never be part of a filesystem tree. They are nameless and
never have a parent.

This allows us to avoid taking a lock in kernfs.InotifyWithParent for such
anonymous inodes.

PiperOrigin-RevId: 538823227
---
 pkg/sentry/fsimpl/cgroupfs/cgroupfs.go        |  5 +++--
 pkg/sentry/fsimpl/devpts/devpts.go            |  1 +
 pkg/sentry/fsimpl/devpts/master.go            |  1 +
 pkg/sentry/fsimpl/devpts/replica.go           |  1 +
 pkg/sentry/fsimpl/fuse/inode.go               |  1 +
 pkg/sentry/fsimpl/host/host.go                |  3 ++-
 .../fsimpl/kernfs/dynamic_bytes_file.go       |  1 +
 pkg/sentry/fsimpl/kernfs/inode_impl_util.go   | 21 +++++++++++++++++++
 pkg/sentry/fsimpl/kernfs/kernfs.go            | 20 +++++++++++++-----
 pkg/sentry/fsimpl/kernfs/kernfs_test.go       |  4 +++-
 pkg/sentry/fsimpl/kernfs/symlink.go           |  1 +
 .../fsimpl/kernfs/synthetic_directory.go      |  1 +
 pkg/sentry/fsimpl/mqfs/root.go                |  1 +
 pkg/sentry/fsimpl/pipefs/pipefs.go            |  1 +
 pkg/sentry/fsimpl/proc/subtasks.go            |  1 +
 pkg/sentry/fsimpl/proc/task.go                |  1 +
 pkg/sentry/fsimpl/proc/task_fds.go            |  3 +++
 pkg/sentry/fsimpl/proc/task_files.go          |  6 ++++++
 pkg/sentry/fsimpl/proc/tasks.go               |  1 +
 pkg/sentry/fsimpl/proc/tasks_files.go         |  2 ++
 pkg/sentry/fsimpl/sockfs/sockfs.go            |  1 +
 pkg/sentry/fsimpl/sys/kcov.go                 |  1 +
 pkg/sentry/fsimpl/sys/sys.go                  |  3 ++-
 23 files changed, 71 insertions(+), 10 deletions(-)

diff --git a/pkg/sentry/fsimpl/cgroupfs/cgroupfs.go b/pkg/sentry/fsimpl/cgroupfs/cgroupfs.go
index 6529225de..504f5cadf 100644
--- a/pkg/sentry/fsimpl/cgroupfs/cgroupfs.go
+++ b/pkg/sentry/fsimpl/cgroupfs/cgroupfs.go
@@ -496,11 +496,12 @@ func (*implStatFS) StatFS(context.Context, *vfs.Filesystem) (linux.Statfs, error
 //
 // +stateify savable
 type dir struct {
-	kernfs.InodeNoopRefCount
 	kernfs.InodeAlwaysValid
 	kernfs.InodeAttrs
-	kernfs.InodeNotSymlink
 	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
+	kernfs.InodeNotSymlink
 	kernfs.InodeWatches
 	kernfs.OrderedChildren
 	implStatFS
diff --git a/pkg/sentry/fsimpl/devpts/devpts.go b/pkg/sentry/fsimpl/devpts/devpts.go
index 7a580de50..f1f6c6781 100644
--- a/pkg/sentry/fsimpl/devpts/devpts.go
+++ b/pkg/sentry/fsimpl/devpts/devpts.go
@@ -150,6 +150,7 @@ type rootInode struct {
 	kernfs.InodeAlwaysValid
 	kernfs.InodeAttrs
 	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary // This holds no meaning as this inode can't be Looked up and is always valid.
 	kernfs.InodeWatches
diff --git a/pkg/sentry/fsimpl/devpts/master.go b/pkg/sentry/fsimpl/devpts/master.go
index 3153229b4..62b651706 100644
--- a/pkg/sentry/fsimpl/devpts/master.go
+++ b/pkg/sentry/fsimpl/devpts/master.go
@@ -36,6 +36,7 @@ type masterInode struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
 	kernfs.InodeWatches
diff --git a/pkg/sentry/fsimpl/devpts/replica.go b/pkg/sentry/fsimpl/devpts/replica.go
index 6f9c29c6b..68614690f 100644
--- a/pkg/sentry/fsimpl/devpts/replica.go
+++ b/pkg/sentry/fsimpl/devpts/replica.go
@@ -35,6 +35,7 @@ type replicaInode struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
 	kernfs.InodeWatches
diff --git a/pkg/sentry/fsimpl/fuse/inode.go b/pkg/sentry/fsimpl/fuse/inode.go
index ab8fdfc8d..740a568f7 100644
--- a/pkg/sentry/fsimpl/fuse/inode.go
+++ b/pkg/sentry/fsimpl/fuse/inode.go
@@ -45,6 +45,7 @@ type fileHandle struct {
 type inode struct {
 	inodeRefs
 	kernfs.InodeAlwaysValid
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotSymlink
 	kernfs.InodeWatches
 	kernfs.OrderedChildren
diff --git a/pkg/sentry/fsimpl/host/host.go b/pkg/sentry/fsimpl/host/host.go
index c7aea8303..894e199dc 100644
--- a/pkg/sentry/fsimpl/host/host.go
+++ b/pkg/sentry/fsimpl/host/host.go
@@ -94,10 +94,11 @@ func isEpollable(fd int) bool {
 //
 // +stateify savable
 type inode struct {
+	kernfs.CachedMappable
 	kernfs.InodeNoStatFS
+	kernfs.InodeAnonymous // inode is effectively anonymous because it represents a donated FD.
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
-	kernfs.CachedMappable
 	kernfs.InodeTemporary // This holds no meaning as this inode can't be Looked up and is always valid.
 	kernfs.InodeWatches
 
diff --git a/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go b/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
index 8fece48c4..52ed496d7 100644
--- a/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
+++ b/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
@@ -38,6 +38,7 @@ type DynamicBytesFile struct {
 	InodeAttrs
 	InodeNoStatFS
 	InodeNoopRefCount
+	InodeNotAnonymous
 	InodeNotDirectory
 	InodeNotSymlink
 	InodeWatches
diff --git a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
index 6caa7fc67..db54a5057 100644
--- a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
+++ b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
@@ -724,6 +724,7 @@ type StaticDirectory struct {
 	InodeAttrs
 	InodeDirectoryNoNewChildren
 	InodeNoStatFS
+	InodeNotAnonymous
 	InodeNotSymlink
 	InodeTemporary
 	InodeWatches
@@ -819,3 +820,23 @@ type InodeWatches struct {
 func (i *InodeWatches) Watches() *vfs.Watches {
 	return &i.watches
 }
+
+// InodeAnonymous partially implements Inode.
+//
+// +stateify savable
+type InodeAnonymous struct{}
+
+// Anonymous implements Inode.Anonymous
+func (*InodeAnonymous) Anonymous() bool {
+	return true
+}
+
+// InodeNotAnonymous partially implements Inode.
+//
+// +stateify savable
+type InodeNotAnonymous struct{}
+
+// Anonymous implements Inode.Anonymous
+func (*InodeNotAnonymous) Anonymous() bool {
+	return false
+}
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs.go b/pkg/sentry/fsimpl/kernfs/kernfs.go
index f7345be9d..1f0f82104 100644
--- a/pkg/sentry/fsimpl/kernfs/kernfs.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs.go
@@ -514,12 +514,18 @@ func (d *Dentry) InotifyWithParent(ctx context.Context, events, cookie uint32, e
 		events |= linux.IN_ISDIR
 	}
 
-	d.fs.mu.RLock()
-	defer d.fs.mu.RUnlock()
-	// The ordering below is important, Linux always notifies the parent first.
-	if d.parent != nil {
-		d.parent.inode.Watches().Notify(ctx, d.name, events, cookie, et, d.isDeleted())
+	// Linux always notifies the parent first.
+
+	// Don't bother looking for a parent if the inode is anonymous. It
+	// won't have one.
+	if !d.inode.Anonymous() {
+		d.fs.mu.RLock()
+		if d.parent != nil {
+			d.parent.inode.Watches().Notify(ctx, d.name, events, cookie, et, d.isDeleted())
+		}
+		d.fs.mu.RUnlock()
 	}
+
 	d.inode.Watches().Notify(ctx, "", events, cookie, et, d.isDeleted())
 }
 
@@ -704,6 +710,10 @@ type Inode interface {
 
 	// Watches returns the set of inotify watches associated with this inode.
 	Watches() *vfs.Watches
+
+	// Anonymous indicates that the Inode is anonymous. It will never have
+	// a name or parent.
+	Anonymous() bool
 }
 
 type inodeRefs interface {
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs_test.go b/pkg/sentry/fsimpl/kernfs/kernfs_test.go
index bcc6ec94a..1ece17057 100644
--- a/pkg/sentry/fsimpl/kernfs/kernfs_test.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs_test.go
@@ -104,6 +104,7 @@ type readonlyDir struct {
 	kernfs.InodeAlwaysValid
 	kernfs.InodeDirectoryNoNewChildren
 	kernfs.InodeNoStatFS
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary
 	kernfs.InodeWatches
@@ -139,8 +140,9 @@ type dir struct {
 	dirRefs
 	attrs
 	kernfs.InodeAlwaysValid
-	kernfs.InodeNotSymlink
 	kernfs.InodeNoStatFS
+	kernfs.InodeNotAnonymous
+	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary
 	kernfs.InodeWatches
 	kernfs.OrderedChildren
diff --git a/pkg/sentry/fsimpl/kernfs/symlink.go b/pkg/sentry/fsimpl/kernfs/symlink.go
index a127804bf..0c9a7b3a6 100644
--- a/pkg/sentry/fsimpl/kernfs/symlink.go
+++ b/pkg/sentry/fsimpl/kernfs/symlink.go
@@ -29,6 +29,7 @@ import (
 type StaticSymlink struct {
 	InodeAttrs
 	InodeNoopRefCount
+	InodeNotAnonymous
 	InodeSymlink
 	InodeNoStatFS
 	InodeWatches
diff --git a/pkg/sentry/fsimpl/kernfs/synthetic_directory.go b/pkg/sentry/fsimpl/kernfs/synthetic_directory.go
index ed587bf47..4b28181d5 100644
--- a/pkg/sentry/fsimpl/kernfs/synthetic_directory.go
+++ b/pkg/sentry/fsimpl/kernfs/synthetic_directory.go
@@ -32,6 +32,7 @@ type syntheticDirectory struct {
 	InodeAlwaysValid
 	InodeAttrs
 	InodeNoStatFS
+	InodeNotAnonymous
 	InodeNotSymlink
 	InodeWatches
 	OrderedChildren
diff --git a/pkg/sentry/fsimpl/mqfs/root.go b/pkg/sentry/fsimpl/mqfs/root.go
index 4a3e950ba..7c26e2219 100644
--- a/pkg/sentry/fsimpl/mqfs/root.go
+++ b/pkg/sentry/fsimpl/mqfs/root.go
@@ -29,6 +29,7 @@ import (
 type rootInode struct {
 	rootInodeRefs
 	kernfs.InodeAlwaysValid
+	kernfs.InodeAnonymous
 	kernfs.InodeAttrs
 	kernfs.InodeDirectoryNoNewChildren
 	kernfs.InodeNotSymlink
diff --git a/pkg/sentry/fsimpl/pipefs/pipefs.go b/pkg/sentry/fsimpl/pipefs/pipefs.go
index f5ebb7e77..6e26ad2b2 100644
--- a/pkg/sentry/fsimpl/pipefs/pipefs.go
+++ b/pkg/sentry/fsimpl/pipefs/pipefs.go
@@ -89,6 +89,7 @@ func (fs *filesystem) MountOptions() string {
 //
 // +stateify savable
 type inode struct {
+	kernfs.InodeAnonymous
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
 	kernfs.InodeNoopRefCount
diff --git a/pkg/sentry/fsimpl/proc/subtasks.go b/pkg/sentry/fsimpl/proc/subtasks.go
index 5dec43bac..60e4dcb07 100644
--- a/pkg/sentry/fsimpl/proc/subtasks.go
+++ b/pkg/sentry/fsimpl/proc/subtasks.go
@@ -35,6 +35,7 @@ type subtasksInode struct {
 	kernfs.InodeAlwaysValid
 	kernfs.InodeAttrs
 	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary
 	kernfs.InodeWatches
diff --git a/pkg/sentry/fsimpl/proc/task.go b/pkg/sentry/fsimpl/proc/task.go
index c90c10b40..89ce31d64 100644
--- a/pkg/sentry/fsimpl/proc/task.go
+++ b/pkg/sentry/fsimpl/proc/task.go
@@ -35,6 +35,7 @@ type taskInode struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary
 	kernfs.InodeWatches
diff --git a/pkg/sentry/fsimpl/proc/task_fds.go b/pkg/sentry/fsimpl/proc/task_fds.go
index 94ed13bec..117b063e5 100644
--- a/pkg/sentry/fsimpl/proc/task_fds.go
+++ b/pkg/sentry/fsimpl/proc/task_fds.go
@@ -113,6 +113,7 @@ type fdDirInode struct {
 	kernfs.InodeAlwaysValid
 	kernfs.InodeAttrs
 	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary
 	kernfs.InodeWatches
@@ -198,6 +199,7 @@ type fdSymlink struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeSymlink
 	kernfs.InodeWatches
 
@@ -257,6 +259,7 @@ type fdInfoDirInode struct {
 	kernfs.InodeAlwaysValid
 	kernfs.InodeAttrs
 	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary
 	kernfs.InodeWatches
diff --git a/pkg/sentry/fsimpl/proc/task_files.go b/pkg/sentry/fsimpl/proc/task_files.go
index d3792a1ee..da24fdc12 100644
--- a/pkg/sentry/fsimpl/proc/task_files.go
+++ b/pkg/sentry/fsimpl/proc/task_files.go
@@ -410,6 +410,7 @@ type memInode struct {
 	kernfs.InodeAttrs
 	kernfs.InodeNoStatFS
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
 	kernfs.InodeWatches
@@ -730,6 +731,7 @@ type statusInode struct {
 	kernfs.InodeAttrs
 	kernfs.InodeNoStatFS
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
 	kernfs.InodeWatches
@@ -963,6 +965,7 @@ type exeSymlink struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeSymlink
 	kernfs.InodeWatches
 
@@ -1035,6 +1038,7 @@ type cwdSymlink struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeSymlink
 	kernfs.InodeWatches
 
@@ -1096,6 +1100,7 @@ type rootSymlink struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeSymlink
 	kernfs.InodeWatches
 
@@ -1269,6 +1274,7 @@ type namespaceInode struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
 	kernfs.InodeWatches
diff --git a/pkg/sentry/fsimpl/proc/tasks.go b/pkg/sentry/fsimpl/proc/tasks.go
index 4d4126d1f..b9c743b5c 100644
--- a/pkg/sentry/fsimpl/proc/tasks.go
+++ b/pkg/sentry/fsimpl/proc/tasks.go
@@ -41,6 +41,7 @@ type tasksInode struct {
 	kernfs.InodeAlwaysValid
 	kernfs.InodeAttrs
 	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary // This holds no meaning as this inode can't be Looked up and is always valid.
 	kernfs.InodeWatches
diff --git a/pkg/sentry/fsimpl/proc/tasks_files.go b/pkg/sentry/fsimpl/proc/tasks_files.go
index a28f46a7b..5a1222601 100644
--- a/pkg/sentry/fsimpl/proc/tasks_files.go
+++ b/pkg/sentry/fsimpl/proc/tasks_files.go
@@ -37,6 +37,7 @@ type selfSymlink struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeSymlink
 	kernfs.InodeWatches
 
@@ -79,6 +80,7 @@ type threadSelfSymlink struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeSymlink
 	kernfs.InodeWatches
 
diff --git a/pkg/sentry/fsimpl/sockfs/sockfs.go b/pkg/sentry/fsimpl/sockfs/sockfs.go
index 290d55b8d..455481447 100644
--- a/pkg/sentry/fsimpl/sockfs/sockfs.go
+++ b/pkg/sentry/fsimpl/sockfs/sockfs.go
@@ -94,6 +94,7 @@ func (fs *filesystem) MountOptions() string {
 //
 // +stateify savable
 type inode struct {
+	kernfs.InodeAnonymous
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
 	kernfs.InodeNotDirectory
diff --git a/pkg/sentry/fsimpl/sys/kcov.go b/pkg/sentry/fsimpl/sys/kcov.go
index 24846a0a5..f71313543 100644
--- a/pkg/sentry/fsimpl/sys/kcov.go
+++ b/pkg/sentry/fsimpl/sys/kcov.go
@@ -39,6 +39,7 @@ func (fs *filesystem) newKcovFile(ctx context.Context, creds *auth.Credentials)
 type kcovInode struct {
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
 	kernfs.InodeWatches
diff --git a/pkg/sentry/fsimpl/sys/sys.go b/pkg/sentry/fsimpl/sys/sys.go
index b0d4e27fe..6bebcf736 100644
--- a/pkg/sentry/fsimpl/sys/sys.go
+++ b/pkg/sentry/fsimpl/sys/sys.go
@@ -199,8 +199,9 @@ type dir struct {
 	dirRefs
 	kernfs.InodeAlwaysValid
 	kernfs.InodeAttrs
-	kernfs.InodeNotSymlink
 	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotAnonymous
+	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary
 	kernfs.InodeWatches
 	kernfs.OrderedChildren