Fix socket record leak in VFS2

VFS2 socket record is not removed from the system-wide
socket table when the socket is released, which will lead
to a memory leak. This patch fixes this issue.

Fixes: #3874

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>

2 files changed, 51 insertions, 16 deletions

diff --git a/pkg/sentry/kernel/BUILD b/pkg/sentry/kernel/BUILD
index a868ee7fe..083071b5e 100644
--- a/pkg/sentry/kernel/BUILD
+++ b/pkg/sentry/kernel/BUILD
@@ -69,8 +69,8 @@ go_template_instance(
     prefix = "socket",
     template = "//pkg/ilist:generic_list",
     types = {
-        "Element": "*SocketRecord",
-        "Linker": "*SocketRecord",
+        "Element": "*SocketRecordVFS1",
+        "Linker": "*SocketRecordVFS1",
     },
 )
 
diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index ebd2ec3df..d9c62ff91 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/pkg/sentry/kernel/kernel.go
@@ -220,10 +220,15 @@ type Kernel struct {
 	// danglingEndpoints is used to save / restore tcpip.DanglingEndpoints.
 	danglingEndpoints struct{} `state:".([]tcpip.Endpoint)"`
 
-	// sockets is the list of all network sockets the system. Protected by
-	// extMu.
+	// sockets is the list of all network sockets in the system.
+	// Protected by extMu.
+	// TODO(gvisor.dev/issue/1624): Only used by VFS1.
 	sockets socketList
 
+	// socketsVFS2 records all network sockets in the system. Protected by
+	// extMu.
+	socketsVFS2 map[*vfs.FileDescription]*SocketRecord
+
 	// nextSocketRecord is the next entry number to use in sockets. Protected
 	// by extMu.
 	nextSocketRecord uint64
@@ -414,6 +419,8 @@ func (k *Kernel) Init(args InitKernelArgs) error {
 			return fmt.Errorf("failed to create sockfs mount: %v", err)
 		}
 		k.socketMount = socketMount
+
+		k.socketsVFS2 = make(map[*vfs.FileDescription]*SocketRecord)
 	}
 
 	return nil
@@ -1509,20 +1516,27 @@ func (k *Kernel) SupervisorContext() context.Context {
 	}
 }
 
-// SocketRecord represents a socket recorded in Kernel.sockets. It implements
-// refs.WeakRefUser for sockets stored in the socket table.
+// SocketRecord represents a socket recorded in Kernel.socketsVFS2.
 //
 // +stateify savable
 type SocketRecord struct {
-	socketEntry
 	k        *Kernel
-	Sock     *refs.WeakRef
-	SockVFS2 *vfs.FileDescription
-	ID       uint64 // Socket table entry number.
+	Sock     *refs.WeakRef        // TODO(gvisor.dev/issue/1624): Only used by VFS1.
+	SockVFS2 *vfs.FileDescription // Only used by VFS2.
+	ID       uint64               // Socket table entry number.
+}
+
+// SocketRecordVFS1 represents a socket recorded in Kernel.sockets. It implements
+// refs.WeakRefUser for sockets stored in the socket table.
+//
+// +stateify savable
+type SocketRecordVFS1 struct {
+	socketEntry
+	SocketRecord
 }
 
 // WeakRefGone implements refs.WeakRefUser.WeakRefGone.
-func (s *SocketRecord) WeakRefGone(context.Context) {
+func (s *SocketRecordVFS1) WeakRefGone(context.Context) {
 	s.k.extMu.Lock()
 	s.k.sockets.Remove(s)
 	s.k.extMu.Unlock()
@@ -1535,7 +1549,12 @@ func (k *Kernel) RecordSocket(sock *fs.File) {
 	k.extMu.Lock()
 	id := k.nextSocketRecord
 	k.nextSocketRecord++
-	s := &SocketRecord{k: k, ID: id}
+	s := &SocketRecordVFS1{
+		SocketRecord: SocketRecord{
+			k:  k,
+			ID: id,
+		},
+	}
 	s.Sock = refs.NewWeakRef(sock, s)
 	k.sockets.PushBack(s)
 	k.extMu.Unlock()
@@ -1547,9 +1566,12 @@ func (k *Kernel) RecordSocket(sock *fs.File) {
 // Precondition: Caller must hold a reference to sock.
 //
 // Note that the socket table will not hold a reference on the
-// vfs.FileDescription, because we do not support weak refs on VFS2 files.
+// vfs.FileDescription.
 func (k *Kernel) RecordSocketVFS2(sock *vfs.FileDescription) {
 	k.extMu.Lock()
+	if _, ok := k.socketsVFS2[sock]; ok {
+		panic(fmt.Sprintf("Socket %p added twice", sock))
+	}
 	id := k.nextSocketRecord
 	k.nextSocketRecord++
 	s := &SocketRecord{
@@ -1557,7 +1579,14 @@ func (k *Kernel) RecordSocketVFS2(sock *vfs.FileDescription) {
 		ID:       id,
 		SockVFS2: sock,
 	}
-	k.sockets.PushBack(s)
+	k.socketsVFS2[sock] = s
+	k.extMu.Unlock()
+}
+
+// DeleteSocketVFS2 removes a VFS2 socket from the system-wide socket table.
+func (k *Kernel) DeleteSocketVFS2(sock *vfs.FileDescription) {
+	k.extMu.Lock()
+	delete(k.socketsVFS2, sock)
 	k.extMu.Unlock()
 }
 
@@ -1568,8 +1597,14 @@ func (k *Kernel) RecordSocketVFS2(sock *vfs.FileDescription) {
 func (k *Kernel) ListSockets() []*SocketRecord {
 	k.extMu.Lock()
 	var socks []*SocketRecord
-	for s := k.sockets.Front(); s != nil; s = s.Next() {
-		socks = append(socks, s)
+	if VFS2Enabled {
+		for _, s := range k.socketsVFS2 {
+			socks = append(socks, s)
+		}
+	} else {
+		for s := k.sockets.Front(); s != nil; s = s.Next() {
+			socks = append(socks, &s.SocketRecord)
+		}
 	}
 	k.extMu.Unlock()
 	return socks