Fix copylocks error about copying IPTables.

IPTables.connections contains a sync.RWMutex. Copying it will trigger copylocks
analysis. Tested by manually enabling nogo tests.

sync.RWMutex is added to IPTables for the additional race condition discovered.

PiperOrigin-RevId: 314817019

pkg/sentry/socket/netfilter/netfilter.go

@@ -144,31 +144,27 @@ func GetEntries(t *kernel.Task, stack *stack.Stack, outPtr usermem.Addr, outLen
 }
 
 func findTable(stk *stack.Stack, tablename linux.TableName) (stack.Table, error) {
-	ipt := stk.IPTables()
-	table, ok := ipt.Tables[tablename.String()]
+	table, ok := stk.IPTables().GetTable(tablename.String())
 	if !ok {
 		return stack.Table{}, fmt.Errorf("couldn't find table %q", tablename)
 	}
 	return table, nil
 }
 
-// FillDefaultIPTables sets stack's IPTables to the default tables and
-// populates them with metadata.
-func FillDefaultIPTables(stk *stack.Stack) {
-	ipt := stack.DefaultTables()
-
-	// In order to fill in the metadata, we have to translate ipt from its
-	// netstack format to Linux's giant-binary-blob format.
-	for name, table := range ipt.Tables {
-		_, metadata, err := convertNetstackToBinary(name, table)
-		if err != nil {
-			panic(fmt.Errorf("Unable to set default IP tables: %v", err))
+// FillIPTablesMetadata populates stack's IPTables with metadata.
+func FillIPTablesMetadata(stk *stack.Stack) {
+	stk.IPTables().ModifyTables(func(tables map[string]stack.Table) {
+		// In order to fill in the metadata, we have to translate ipt from its
+		// netstack format to Linux's giant-binary-blob format.
+		for name, table := range tables {
+			_, metadata, err := convertNetstackToBinary(name, table)
+			if err != nil {
+				panic(fmt.Errorf("Unable to set default IP tables: %v", err))
+			}
+			table.SetMetadata(metadata)
+			tables[name] = table
 		}
-		table.SetMetadata(metadata)
-		ipt.Tables[name] = table
-	}
-
-	stk.SetIPTables(ipt)
+	})
 }
 
 // convertNetstackToBinary converts the iptables as stored in netstack to the
@@ -573,15 +569,13 @@ func SetEntries(stk *stack.Stack, optVal []byte) *syserr.Error {
 	// - There are no chains without an unconditional final rule.
 	// - There are no chains without an unconditional underflow rule.
 
-	ipt := stk.IPTables()
 	table.SetMetadata(metadata{
 		HookEntry:  replace.HookEntry,
 		Underflow:  replace.Underflow,
 		NumEntries: replace.NumEntries,
 		Size:       replace.Size,
 	})
-	ipt.Tables[replace.Name.String()] = table
-	stk.SetIPTables(ipt)
+	stk.IPTables().ReplaceTable(replace.Name.String(), table)
 
 	return nil
 }

pkg/sentry/socket/netstack/stack.go

@@ -362,14 +362,13 @@ func (s *Stack) RouteTable() []inet.Route {
 }
 
 // IPTables returns the stack's iptables.
-func (s *Stack) IPTables() (stack.IPTables, error) {
+func (s *Stack) IPTables() (*stack.IPTables, error) {
 	return s.Stack.IPTables(), nil
 }
 
-// FillDefaultIPTables sets the stack's iptables to the default tables, which
-// allow and do not modify all traffic.
-func (s *Stack) FillDefaultIPTables() {
-	netfilter.FillDefaultIPTables(s.Stack)
+// FillIPTablesMetadata populates stack's IPTables with metadata.
+func (s *Stack) FillIPTablesMetadata() {
+	netfilter.FillIPTablesMetadata(s.Stack)
 }
 
 // Resume implements inet.Stack.Resume.

pkg/tcpip/stack/iptables.go

@@ -43,11 +43,11 @@ const HookUnset = -1
 
 // DefaultTables returns a default set of tables. Each chain is set to accept
 // all packets.
-func DefaultTables() IPTables {
+func DefaultTables() *IPTables {
 	// TODO(gvisor.dev/issue/170): We may be able to swap out some strings for
 	// iotas.
-	return IPTables{
-		Tables: map[string]Table{
+	return &IPTables{
+		tables: map[string]Table{
 			TablenameNat: Table{
 				Rules: []Rule{
 					Rule{Target: AcceptTarget{}},
@@ -106,7 +106,7 @@ func DefaultTables() IPTables {
 				UserChains: map[string]int{},
 			},
 		},
-		Priorities: map[Hook][]string{
+		priorities: map[Hook][]string{
 			Input:      []string{TablenameNat, TablenameFilter},
 			Prerouting: []string{TablenameMangle, TablenameNat},
 			Output:     []string{TablenameMangle, TablenameNat, TablenameFilter},
@@ -158,6 +158,36 @@ func EmptyNatTable() Table {
 	}
 }
 
+// GetTable returns table by name.
+func (it *IPTables) GetTable(name string) (Table, bool) {
+	it.mu.RLock()
+	defer it.mu.RUnlock()
+	t, ok := it.tables[name]
+	return t, ok
+}
+
+// ReplaceTable replaces or inserts table by name.
+func (it *IPTables) ReplaceTable(name string, table Table) {
+	it.mu.Lock()
+	defer it.mu.Unlock()
+	it.tables[name] = table
+}
+
+// ModifyTables acquires write-lock and calls fn with internal name-to-table
+// map. This function can be used to update multiple tables atomically.
+func (it *IPTables) ModifyTables(fn func(map[string]Table)) {
+	it.mu.Lock()
+	defer it.mu.Unlock()
+	fn(it.tables)
+}
+
+// GetPriorities returns slice of priorities associated with hook.
+func (it *IPTables) GetPriorities(hook Hook) []string {
+	it.mu.RLock()
+	defer it.mu.RUnlock()
+	return it.priorities[hook]
+}
+
 // A chainVerdict is what a table decides should be done with a packet.
 type chainVerdict int
 
@@ -184,8 +214,8 @@ func (it *IPTables) Check(hook Hook, pkt *PacketBuffer, gso *GSO, r *Route, addr
 	it.connections.HandlePacket(pkt, hook, gso, r)
 
 	// Go through each table containing the hook.
-	for _, tablename := range it.Priorities[hook] {
-		table := it.Tables[tablename]
+	for _, tablename := range it.GetPriorities(hook) {
+		table, _ := it.GetTable(tablename)
 		ruleIdx := table.BuiltinChains[hook]
 		switch verdict := it.checkChain(hook, pkt, table, ruleIdx, gso, r, address, nicName); verdict {
 		// If the table returns Accept, move on to the next table.

pkg/tcpip/stack/iptables_types.go

@@ -16,6 +16,7 @@ package stack
 
 import (
 	"strings"
+	"sync"
 
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
@@ -78,13 +79,17 @@ const (
 
 // IPTables holds all the tables for a netstack.
 type IPTables struct {
-	// Tables maps table names to tables. User tables have arbitrary names.
-	Tables map[string]Table
+	// mu protects tables and priorities.
+	mu sync.RWMutex
 
-	// Priorities maps each hook to a list of table names. The order of the
+	// tables maps table names to tables. User tables have arbitrary names. mu
+	// needs to be locked for accessing.
+	tables map[string]Table
+
+	// priorities maps each hook to a list of table names. The order of the
 	// list is the order in which each table should be visited for that
-	// hook.
-	Priorities map[Hook][]string
+	// hook. mu needs to be locked for accessing.
+	priorities map[Hook][]string
 
 	connections ConnTrackTable
 }

pkg/tcpip/stack/stack.go

@@ -424,12 +424,8 @@ type Stack struct {
 	// handleLocal allows non-loopback interfaces to loop packets.
 	handleLocal bool
 
-	// tablesMu protects iptables.
-	tablesMu sync.RWMutex
-
-	// tables are the iptables packet filtering and manipulation rules. The are
-	// protected by tablesMu.`
-	tables IPTables
+	// tables are the iptables packet filtering and manipulation rules.
+	tables *IPTables
 
 	// resumableEndpoints is a list of endpoints that need to be resumed if the
 	// stack is being restored.
@@ -676,6 +672,7 @@ func New(opts Options) *Stack {
 		clock:                clock,
 		stats:                opts.Stats.FillIn(),
 		handleLocal:          opts.HandleLocal,
+		tables:               DefaultTables(),
 		icmpRateLimiter:      NewICMPRateLimiter(),
 		seed:                 generateRandUint32(),
 		ndpConfigs:           opts.NDPConfigs,
@@ -1741,18 +1738,8 @@ func (s *Stack) IsInGroup(nicID tcpip.NICID, multicastAddr tcpip.Address) (bool,
 }
 
 // IPTables returns the stack's iptables.
-func (s *Stack) IPTables() IPTables {
-	s.tablesMu.RLock()
-	t := s.tables
-	s.tablesMu.RUnlock()
-	return t
-}
-
-// SetIPTables sets the stack's iptables.
-func (s *Stack) SetIPTables(ipt IPTables) {
-	s.tablesMu.Lock()
-	s.tables = ipt
-	s.tablesMu.Unlock()
+func (s *Stack) IPTables() *IPTables {
+	return s.tables
 }
 
 // ICMPLimit returns the maximum number of ICMP messages that can be sent

pkg/tcpip/transport/icmp/endpoint.go

@@ -140,11 +140,6 @@ func (e *endpoint) SetOwner(owner tcpip.PacketOwner) {
 	e.owner = owner
 }
 
-// IPTables implements tcpip.Endpoint.IPTables.
-func (e *endpoint) IPTables() (stack.IPTables, error) {
-	return e.stack.IPTables(), nil
-}
-
 // Read reads data from the endpoint. This method does not block if
 // there is no data pending.
 func (e *endpoint) Read(addr *tcpip.FullAddress) (buffer.View, tcpip.ControlMessages, *tcpip.Error) {

pkg/tcpip/transport/packet/endpoint.go

@@ -132,11 +132,6 @@ func (ep *endpoint) Close() {
 // ModerateRecvBuf implements tcpip.Endpoint.ModerateRecvBuf.
 func (ep *endpoint) ModerateRecvBuf(copied int) {}
 
-// IPTables implements tcpip.Endpoint.IPTables.
-func (ep *endpoint) IPTables() (stack.IPTables, error) {
-	return ep.stack.IPTables(), nil
-}
-
 // Read implements tcpip.Endpoint.Read.
 func (ep *endpoint) Read(addr *tcpip.FullAddress) (buffer.View, tcpip.ControlMessages, *tcpip.Error) {
 	ep.rcvMu.Lock()

pkg/tcpip/transport/raw/endpoint.go

@@ -166,11 +166,6 @@ func (e *endpoint) SetOwner(owner tcpip.PacketOwner) {
 	e.owner = owner
 }
 
-// IPTables implements tcpip.Endpoint.IPTables.
-func (e *endpoint) IPTables() (stack.IPTables, error) {
-	return e.stack.IPTables(), nil
-}
-
 // Read implements tcpip.Endpoint.Read.
 func (e *endpoint) Read(addr *tcpip.FullAddress) (buffer.View, tcpip.ControlMessages, *tcpip.Error) {
 	if !e.associated {

pkg/tcpip/transport/tcp/endpoint.go

@@ -1172,11 +1172,6 @@ func (e *endpoint) SetOwner(owner tcpip.PacketOwner) {
 	e.owner = owner
 }
 
-// IPTables implements tcpip.Endpoint.IPTables.
-func (e *endpoint) IPTables() (stack.IPTables, error) {
-	return e.stack.IPTables(), nil
-}
-
 // Read reads data from the endpoint.
 func (e *endpoint) Read(*tcpip.FullAddress) (buffer.View, tcpip.ControlMessages, *tcpip.Error) {
 	e.LockUser()

pkg/tcpip/transport/udp/endpoint.go

@@ -247,11 +247,6 @@ func (e *endpoint) Close() {
 // ModerateRecvBuf implements tcpip.Endpoint.ModerateRecvBuf.
 func (e *endpoint) ModerateRecvBuf(copied int) {}
 
-// IPTables implements tcpip.Endpoint.IPTables.
-func (e *endpoint) IPTables() (stack.IPTables, error) {
-	return e.stack.IPTables(), nil
-}
-
 // Read reads data from the endpoint. This method does not block if
 // there is no data pending.
 func (e *endpoint) Read(addr *tcpip.FullAddress) (buffer.View, tcpip.ControlMessages, *tcpip.Error) {

runsc/boot/loader.go

@@ -1056,7 +1056,7 @@ func newEmptySandboxNetworkStack(clock tcpip.Clock, uniqueID stack.UniqueID) (in
 		return nil, fmt.Errorf("SetTransportProtocolOption failed: %v", err)
 	}
 
-	s.FillDefaultIPTables()
+	s.FillIPTablesMetadata()
 
 	return &s, nil
 }