Correctly return EMSGSIZE when packet is too big in raw socket.

IPv4 previously accepts the packet, while IPv6 panics. Neither is the behavior
in Linux.

splice() in Linux has different behavior than in gVisor. This change documents
it in the SpliceTooLong test.

Reported-by: syzbot+b550e78e5c24d1d521f2@syzkaller.appspotmail.com
PiperOrigin-RevId: 352091286

2 files changed, 19 insertions, 11 deletions

diff --git a/pkg/tcpip/network/ipv4/igmp.go b/pkg/tcpip/network/ipv4/igmp.go
index da88d65d1..d9b5fe6ed 100644
--- a/pkg/tcpip/network/ipv4/igmp.go
+++ b/pkg/tcpip/network/ipv4/igmp.go
@@ -262,13 +262,15 @@ func (igmp *igmpState) writePacket(destAddress tcpip.Address, groupAddress tcpip
 	localAddr := addressEndpoint.AddressWithPrefix().Address
 	addressEndpoint.DecRef()
 	addressEndpoint = nil
-	igmp.ep.addIPHeader(localAddr, destAddress, pkt, stack.NetworkHeaderParams{
+	if err := igmp.ep.addIPHeader(localAddr, destAddress, pkt, stack.NetworkHeaderParams{
 		Protocol: header.IGMPProtocolNumber,
 		TTL:      header.IGMPTTL,
 		TOS:      stack.DefaultTOS,
 	}, header.IPv4OptionsSerializer{
 		&header.IPv4SerializableRouterAlertOption{},
-	})
+	}); err != nil {
+		panic(fmt.Sprintf("failed to add IP header: %s", err))
+	}
 
 	sentStats := igmp.ep.protocol.stack.Stats().IGMP.PacketsSent
 	if err := igmp.ep.nic.WritePacketToRemote(header.EthernetAddressFromMulticastIPv4Address(destAddress), nil /* gso */, ProtocolNumber, pkt); err != nil {
diff --git a/pkg/tcpip/network/ipv4/ipv4.go b/pkg/tcpip/network/ipv4/ipv4.go
index cc045c7a9..bb25a76fe 100644
--- a/pkg/tcpip/network/ipv4/ipv4.go
+++ b/pkg/tcpip/network/ipv4/ipv4.go
@@ -237,7 +237,7 @@ func (e *endpoint) NetworkProtocolNumber() tcpip.NetworkProtocolNumber {
 	return e.protocol.Number()
 }
 
-func (e *endpoint) addIPHeader(srcAddr, dstAddr tcpip.Address, pkt *stack.PacketBuffer, params stack.NetworkHeaderParams, options header.IPv4OptionsSerializer) {
+func (e *endpoint) addIPHeader(srcAddr, dstAddr tcpip.Address, pkt *stack.PacketBuffer, params stack.NetworkHeaderParams, options header.IPv4OptionsSerializer) *tcpip.Error {
 	hdrLen := header.IPv4MinimumSize
 	var optLen int
 	if options != nil {
@@ -245,19 +245,19 @@ func (e *endpoint) addIPHeader(srcAddr, dstAddr tcpip.Address, pkt *stack.Packet
 	}
 	hdrLen += optLen
 	if hdrLen > header.IPv4MaximumHeaderSize {
-		// Since we have no way to report an error we must either panic or create
-		// a packet which is different to what was requested. Choose panic as this
-		// would be a programming error that should be caught in testing.
-		panic(fmt.Sprintf("IPv4 Options %d bytes, Max %d", optLen, header.IPv4MaximumOptionsSize))
+		return tcpip.ErrMessageTooLong
 	}
 	ip := header.IPv4(pkt.NetworkHeader().Push(hdrLen))
-	length := uint16(pkt.Size())
+	length := pkt.Size()
+	if length > math.MaxUint16 {
+		return tcpip.ErrMessageTooLong
+	}
 	// RFC 6864 section 4.3 mandates uniqueness of ID values for non-atomic
 	// datagrams. Since the DF bit is never being set here, all datagrams
 	// are non-atomic and need an ID.
 	id := atomic.AddUint32(&e.protocol.ids[hashRoute(srcAddr, dstAddr, params.Protocol, e.protocol.hashIV)%buckets], 1)
 	ip.Encode(&header.IPv4Fields{
-		TotalLength: length,
+		TotalLength: uint16(length),
 		ID:          uint16(id),
 		TTL:         params.TTL,
 		TOS:         params.TOS,
@@ -268,6 +268,7 @@ func (e *endpoint) addIPHeader(srcAddr, dstAddr tcpip.Address, pkt *stack.Packet
 	})
 	ip.SetChecksum(^ip.CalculateChecksum())
 	pkt.NetworkProtocolNumber = ProtocolNumber
+	return nil
 }
 
 // handleFragments fragments pkt and calls the handler function on each
@@ -295,7 +296,9 @@ func (e *endpoint) handleFragments(r *stack.Route, gso *stack.GSO, networkMTU ui
 
 // WritePacket writes a packet to the given destination address and protocol.
 func (e *endpoint) WritePacket(r *stack.Route, gso *stack.GSO, params stack.NetworkHeaderParams, pkt *stack.PacketBuffer) *tcpip.Error {
-	e.addIPHeader(r.LocalAddress, r.RemoteAddress, pkt, params, nil /* options */)
+	if err := e.addIPHeader(r.LocalAddress, r.RemoteAddress, pkt, params, nil /* options */); err != nil {
+		return err
+	}
 
 	// iptables filtering. All packets that reach here are locally
 	// generated.
@@ -383,7 +386,10 @@ func (e *endpoint) WritePackets(r *stack.Route, gso *stack.GSO, pkts stack.Packe
 	}
 
 	for pkt := pkts.Front(); pkt != nil; pkt = pkt.Next() {
-		e.addIPHeader(r.LocalAddress, r.RemoteAddress, pkt, params, nil /* options */)
+		if err := e.addIPHeader(r.LocalAddress, r.RemoteAddress, pkt, params, nil /* options */); err != nil {
+			return 0, err
+		}
+
 		networkMTU, err := calculateNetworkMTU(e.nic.MTU(), uint32(pkt.NetworkHeader().View().Size()))
 		if err != nil {
 			r.Stats().IP.OutgoingPacketErrors.IncrementBy(uint64(pkts.Len()))