iptables: remove metadata struct

Metadata was useful for debugging and safety, but enough tests exist that we
should see failures when (de)serialization is broken. It made stack
initialization more cumbersome and it's also getting in the way of ip6tables.

PiperOrigin-RevId: 317210653

4 files changed, 21 insertions, 112 deletions

diff --git a/pkg/sentry/socket/netfilter/netfilter.go b/pkg/sentry/socket/netfilter/netfilter.go
index 66015e2bc..f7abe77d3 100644
--- a/pkg/sentry/socket/netfilter/netfilter.go
+++ b/pkg/sentry/socket/netfilter/netfilter.go
@@ -41,19 +41,6 @@ const errorTargetName = "ERROR"
 // change the destination port/destination IP for packets.
 const redirectTargetName = "REDIRECT"
 
-// Metadata is used to verify that we are correctly serializing and
-// deserializing iptables into structs consumable by the iptables tool. We save
-// a metadata struct when the tables are written, and when they are read out we
-// verify that certain fields are the same.
-//
-// metadata is used by this serialization/deserializing code, not netstack.
-type metadata struct {
-	HookEntry  [linux.NF_INET_NUMHOOKS]uint32
-	Underflow  [linux.NF_INET_NUMHOOKS]uint32
-	NumEntries uint32
-	Size       uint32
-}
-
 // enableLogging controls whether to log the (de)serialization of netfilter
 // structs between userspace and netstack. These logs are useful when
 // developing iptables, but can pollute sentry logs otherwise.
@@ -83,29 +70,13 @@ func GetInfo(t *kernel.Task, stack *stack.Stack, outPtr usermem.Addr) (linux.IPT
 		return linux.IPTGetinfo{}, syserr.FromError(err)
 	}
 
-	// Find the appropriate table.
-	table, err := findTable(stack, info.Name)
+	_, info, err := convertNetstackToBinary(stack, info.Name)
 	if err != nil {
-		nflog("%v", err)
+		nflog("couldn't convert iptables: %v", err)
 		return linux.IPTGetinfo{}, syserr.ErrInvalidArgument
 	}
 
-	// Get the hooks that apply to this table.
-	info.ValidHooks = table.ValidHooks()
-
-	// Grab the metadata struct, which is used to store information (e.g.
-	// the number of entries) that applies to the user's encoding of
-	// iptables, but not netstack's.
-	metadata := table.Metadata().(metadata)
-
-	// Set values from metadata.
-	info.HookEntry = metadata.HookEntry
-	info.Underflow = metadata.Underflow
-	info.NumEntries = metadata.NumEntries
-	info.Size = metadata.Size
-
 	nflog("returning info: %+v", info)
-
 	return info, nil
 }
 
@@ -118,23 +89,13 @@ func GetEntries(t *kernel.Task, stack *stack.Stack, outPtr usermem.Addr, outLen
 		return linux.KernelIPTGetEntries{}, syserr.FromError(err)
 	}
 
-	// Find the appropriate table.
-	table, err := findTable(stack, userEntries.Name)
-	if err != nil {
-		nflog("%v", err)
-		return linux.KernelIPTGetEntries{}, syserr.ErrInvalidArgument
-	}
-
 	// Convert netstack's iptables rules to something that the iptables
 	// tool can understand.
-	entries, meta, err := convertNetstackToBinary(userEntries.Name.String(), table)
+	entries, _, err := convertNetstackToBinary(stack, userEntries.Name)
 	if err != nil {
 		nflog("couldn't read entries: %v", err)
 		return linux.KernelIPTGetEntries{}, syserr.ErrInvalidArgument
 	}
-	if meta != table.Metadata().(metadata) {
-		panic(fmt.Sprintf("Table %q metadata changed between writing and reading. Was saved as %+v, but is now %+v", userEntries.Name.String(), table.Metadata().(metadata), meta))
-	}
 	if binary.Size(entries) > uintptr(outLen) {
 		nflog("insufficient GetEntries output size: %d", uintptr(outLen))
 		return linux.KernelIPTGetEntries{}, syserr.ErrInvalidArgument
@@ -143,44 +104,26 @@ func GetEntries(t *kernel.Task, stack *stack.Stack, outPtr usermem.Addr, outLen
 	return entries, nil
 }
 
-func findTable(stk *stack.Stack, tablename linux.TableName) (stack.Table, error) {
-	table, ok := stk.IPTables().GetTable(tablename.String())
-	if !ok {
-		return stack.Table{}, fmt.Errorf("couldn't find table %q", tablename)
-	}
-	return table, nil
-}
-
-// 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
-		}
-	})
-}
-
 // convertNetstackToBinary converts the iptables as stored in netstack to the
 // format expected by the iptables tool. Linux stores each table as a binary
 // blob that can only be traversed by parsing a bit, reading some offsets,
 // jumping to those offsets, parsing again, etc.
-func convertNetstackToBinary(tablename string, table stack.Table) (linux.KernelIPTGetEntries, metadata, error) {
-	// Return values.
+func convertNetstackToBinary(stack *stack.Stack, tablename linux.TableName) (linux.KernelIPTGetEntries, linux.IPTGetinfo, error) {
+	table, ok := stack.IPTables().GetTable(tablename.String())
+	if !ok {
+		return linux.KernelIPTGetEntries{}, linux.IPTGetinfo{}, fmt.Errorf("couldn't find table %q", tablename)
+	}
+
 	var entries linux.KernelIPTGetEntries
-	var meta metadata
+	var info linux.IPTGetinfo
+	info.ValidHooks = table.ValidHooks()
 
 	// The table name has to fit in the struct.
 	if linux.XT_TABLE_MAXNAMELEN < len(tablename) {
-		return linux.KernelIPTGetEntries{}, metadata{}, fmt.Errorf("table name %q too long.", tablename)
+		return linux.KernelIPTGetEntries{}, linux.IPTGetinfo{}, fmt.Errorf("table name %q too long", tablename)
 	}
-	copy(entries.Name[:], tablename)
+	copy(info.Name[:], tablename[:])
+	copy(entries.Name[:], tablename[:])
 
 	for ruleIdx, rule := range table.Rules {
 		nflog("convert to binary: current offset: %d", entries.Size)
@@ -189,14 +132,14 @@ func convertNetstackToBinary(tablename string, table stack.Table) (linux.KernelI
 		for hook, hookRuleIdx := range table.BuiltinChains {
 			if hookRuleIdx == ruleIdx {
 				nflog("convert to binary: found hook %d at offset %d", hook, entries.Size)
-				meta.HookEntry[hook] = entries.Size
+				info.HookEntry[hook] = entries.Size
 			}
 		}
 		// Is this a chain underflow point?
 		for underflow, underflowRuleIdx := range table.Underflows {
 			if underflowRuleIdx == ruleIdx {
 				nflog("convert to binary: found underflow %d at offset %d", underflow, entries.Size)
-				meta.Underflow[underflow] = entries.Size
+				info.Underflow[underflow] = entries.Size
 			}
 		}
 
@@ -251,12 +194,12 @@ func convertNetstackToBinary(tablename string, table stack.Table) (linux.KernelI
 
 		entries.Size += uint32(entry.NextOffset)
 		entries.Entrytable = append(entries.Entrytable, entry)
-		meta.NumEntries++
+		info.NumEntries++
 	}
 
-	nflog("convert to binary: finished with an marshalled size of %d", meta.Size)
-	meta.Size = entries.Size
-	return entries, meta, nil
+	nflog("convert to binary: finished with an marshalled size of %d", info.Size)
+	info.Size = entries.Size
+	return entries, info, nil
 }
 
 func marshalTarget(target stack.Target) []byte {
@@ -569,12 +512,6 @@ 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.
 
-	table.SetMetadata(metadata{
-		HookEntry:  replace.HookEntry,
-		Underflow:  replace.Underflow,
-		NumEntries: replace.NumEntries,
-		Size:       replace.Size,
-	})
 	stk.IPTables().ReplaceTable(replace.Name.String(), table)
 
 	return nil
diff --git a/pkg/sentry/socket/netstack/stack.go b/pkg/sentry/socket/netstack/stack.go
index f97f9b6f3..ee11742a6 100644
--- a/pkg/sentry/socket/netstack/stack.go
+++ b/pkg/sentry/socket/netstack/stack.go
@@ -18,7 +18,6 @@ import (
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/sentry/inet"
-	"gvisor.dev/gvisor/pkg/sentry/socket/netfilter"
 	"gvisor.dev/gvisor/pkg/syserr"
 	"gvisor.dev/gvisor/pkg/syserror"
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -366,11 +365,6 @@ func (s *Stack) IPTables() (*stack.IPTables, error) {
 	return s.Stack.IPTables(), nil
 }
 
-// FillIPTablesMetadata populates stack's IPTables with metadata.
-func (s *Stack) FillIPTablesMetadata() {
-	netfilter.FillIPTablesMetadata(s.Stack)
-}
-
 // Resume implements inet.Stack.Resume.
 func (s *Stack) Resume() {
 	s.Stack.Resume()
diff --git a/pkg/tcpip/stack/iptables.go b/pkg/tcpip/stack/iptables.go
index 4e9b404c8..dc2b77c9d 100644
--- a/pkg/tcpip/stack/iptables.go
+++ b/pkg/tcpip/stack/iptables.go
@@ -173,14 +173,6 @@ func (it *IPTables) ReplaceTable(name string, table Table) {
 	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()
diff --git a/pkg/tcpip/stack/iptables_types.go b/pkg/tcpip/stack/iptables_types.go
index 4a6a5c6f1..72f1dd329 100644
--- a/pkg/tcpip/stack/iptables_types.go
+++ b/pkg/tcpip/stack/iptables_types.go
@@ -95,7 +95,7 @@ type IPTables struct {
 }
 
 // A Table defines a set of chains and hooks into the network stack. It is
-// really just a list of rules with some metadata for entrypoints and such.
+// really just a list of rules.
 type Table struct {
 	// Rules holds the rules that make up the table.
 	Rules []Rule
@@ -110,10 +110,6 @@ type Table struct {
 	// UserChains holds user-defined chains for the keyed by name. Users
 	// can give their chains arbitrary names.
 	UserChains map[string]int
-
-	// Metadata holds information about the Table that is useful to users
-	// of IPTables, but not to the netstack IPTables code itself.
-	metadata interface{}
 }
 
 // ValidHooks returns a bitmap of the builtin hooks for the given table.
@@ -125,16 +121,6 @@ func (table *Table) ValidHooks() uint32 {
 	return hooks
 }
 
-// Metadata returns the metadata object stored in table.
-func (table *Table) Metadata() interface{} {
-	return table.metadata
-}
-
-// SetMetadata sets the metadata object stored in table.
-func (table *Table) SetMetadata(metadata interface{}) {
-	table.metadata = metadata
-}
-
 // A Rule is a packet processing rule. It consists of two pieces. First it
 // contains zero or more matchers, each of which is a specification of which
 // packets this rule applies to. If there are no matchers in the rule, it