AF_PACKET support for netstack (aka epsocket).

Like (AF_INET, SOCK_RAW) sockets, AF_PACKET sockets require CAP_NET_RAW. With
runsc, you'll need to pass `--net-raw=true` to enable them.

Binding isn't supported yet.

PiperOrigin-RevId: 275909366

pkg/sentry/socket/netstack/netstack.go

@@ -53,6 +53,7 @@ import (
 	"gvisor.dev/gvisor/pkg/syserror"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
+	"gvisor.dev/gvisor/pkg/tcpip/header"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 	"gvisor.dev/gvisor/pkg/tcpip/transport/tcp"
 	"gvisor.dev/gvisor/pkg/tcpip/transport/udp"
@@ -296,6 +297,7 @@ func New(t *kernel.Task, family int, skType linux.SockType, protocol int, queue
 
 var sockAddrInetSize = int(binary.Size(linux.SockAddrInet{}))
 var sockAddrInet6Size = int(binary.Size(linux.SockAddrInet6{}))
+var sockAddrLinkSize = int(binary.Size(linux.SockAddrLink{}))
 
 // bytesToIPAddress converts an IPv4 or IPv6 address from the user to the
 // netstack representation taking any addresses into account.
@@ -307,12 +309,12 @@ func bytesToIPAddress(addr []byte) tcpip.Address {
 }
 
 // AddressAndFamily reads an sockaddr struct from the given address and
-// converts it to the FullAddress format. It supports AF_UNIX, AF_INET and
-// AF_INET6 addresses.
+// converts it to the FullAddress format. It supports AF_UNIX, AF_INET,
+// AF_INET6, and AF_PACKET addresses.
 //
 // strict indicates whether addresses with the AF_UNSPEC family are accepted of not.
 //
-// AddressAndFamily returns an address, its family.
+// AddressAndFamily returns an address and its family.
 func AddressAndFamily(sfamily int, addr []byte, strict bool) (tcpip.FullAddress, uint16, *syserr.Error) {
 	// Make sure we have at least 2 bytes for the address family.
 	if len(addr) < 2 {
@@ -371,6 +373,22 @@ func AddressAndFamily(sfamily int, addr []byte, strict bool) (tcpip.FullAddress,
 		}
 		return out, family, nil
 
+	case linux.AF_PACKET:
+		var a linux.SockAddrLink
+		if len(addr) < sockAddrLinkSize {
+			return tcpip.FullAddress{}, family, syserr.ErrInvalidArgument
+		}
+		binary.Unmarshal(addr[:sockAddrLinkSize], usermem.ByteOrder, &a)
+		if a.Family != linux.AF_PACKET || a.HardwareAddrLen != header.EthernetAddressSize {
+			return tcpip.FullAddress{}, family, syserr.ErrInvalidArgument
+		}
+
+		// TODO(b/129292371): Return protocol too.
+		return tcpip.FullAddress{
+			NIC:  tcpip.NICID(a.InterfaceIndex),
+			Addr: tcpip.Address(a.HardwareAddr[:header.EthernetAddressSize]),
+		}, family, nil
+
 	case linux.AF_UNSPEC:
 		return tcpip.FullAddress{}, family, nil
 
@@ -1951,12 +1969,14 @@ func ConvertAddress(family int, addr tcpip.FullAddress) (linux.SockAddr, uint32)
 			return &out, uint32(2 + l)
 		}
 		return &out, uint32(3 + l)
+
 	case linux.AF_INET:
 		var out linux.SockAddrInet
 		copy(out.Addr[:], addr.Addr)
 		out.Family = linux.AF_INET
 		out.Port = htons(addr.Port)
-		return &out, uint32(binary.Size(out))
+		return &out, uint32(sockAddrInetSize)
+
 	case linux.AF_INET6:
 		var out linux.SockAddrInet6
 		if len(addr.Addr) == 4 {
@@ -1972,7 +1992,17 @@ func ConvertAddress(family int, addr tcpip.FullAddress) (linux.SockAddr, uint32)
 		if isLinkLocal(addr.Addr) {
 			out.Scope_id = uint32(addr.NIC)
 		}
-		return &out, uint32(binary.Size(out))
+		return &out, uint32(sockAddrInet6Size)
+
+	case linux.AF_PACKET:
+		// TODO(b/129292371): Return protocol too.
+		var out linux.SockAddrLink
+		out.Family = linux.AF_PACKET
+		out.InterfaceIndex = int32(addr.NIC)
+		out.HardwareAddrLen = header.EthernetAddressSize
+		copy(out.HardwareAddr[:], addr.Addr)
+		return &out, uint32(sockAddrLinkSize)
+
 	default:
 		return nil, 0
 	}

pkg/sentry/socket/netstack/provider.go

@@ -62,6 +62,10 @@ func getTransportProtocol(ctx context.Context, stype linux.SockType, protocol in
 		}
 
 	case linux.SOCK_RAW:
+		// TODO(b/142504697): "In order to create a raw socket, a
+		// process must have the CAP_NET_RAW capability in the user
+		// namespace that governs its network namespace." - raw(7)
+
 		// Raw sockets require CAP_NET_RAW.
 		creds := auth.CredentialsFromContext(ctx)
 		if !creds.HasCapability(linux.CAP_NET_RAW) {
@@ -85,7 +89,8 @@ func getTransportProtocol(ctx context.Context, stype linux.SockType, protocol in
 	return 0, true, syserr.ErrProtocolNotSupported
 }
 
-// Socket creates a new socket object for the AF_INET or AF_INET6 family.
+// Socket creates a new socket object for the AF_INET, AF_INET6, or AF_PACKET
+// family.
 func (p *provider) Socket(t *kernel.Task, stype linux.SockType, protocol int) (*fs.File, *syserr.Error) {
 	// Fail right away if we don't have a stack.
 	stack := t.NetworkContext()
@@ -99,6 +104,12 @@ func (p *provider) Socket(t *kernel.Task, stype linux.SockType, protocol int) (*
 		return nil, nil
 	}
 
+	// Packet sockets are handled separately, since they are neither INET
+	// nor INET6 specific.
+	if p.family == linux.AF_PACKET {
+		return packetSocket(t, eps, stype, protocol)
+	}
+
 	// Figure out the transport protocol.
 	transProto, associated, err := getTransportProtocol(t, stype, protocol)
 	if err != nil {
@@ -121,12 +132,47 @@ func (p *provider) Socket(t *kernel.Task, stype linux.SockType, protocol int) (*
 	return New(t, p.family, stype, int(transProto), wq, ep)
 }
 
+func packetSocket(t *kernel.Task, epStack *Stack, stype linux.SockType, protocol int) (*fs.File, *syserr.Error) {
+	// TODO(b/142504697): "In order to create a packet socket, a process
+	// must have the CAP_NET_RAW capability in the user namespace that
+	// governs its network namespace." - packet(7)
+
+	// Packet sockets require CAP_NET_RAW.
+	creds := auth.CredentialsFromContext(t)
+	if !creds.HasCapability(linux.CAP_NET_RAW) {
+		return nil, syserr.ErrNotPermitted
+	}
+
+	// "cooked" packets don't contain link layer information.
+	var cooked bool
+	switch stype {
+	case linux.SOCK_DGRAM:
+		cooked = true
+	case linux.SOCK_RAW:
+		cooked = false
+	default:
+		return nil, syserr.ErrProtocolNotSupported
+	}
+
+	// protocol is passed in network byte order, but netstack wants it in
+	// host order.
+	netProto := tcpip.NetworkProtocolNumber(ntohs(uint16(protocol)))
+
+	wq := &waiter.Queue{}
+	ep, err := epStack.Stack.NewPacketEndpoint(cooked, netProto, wq)
+	if err != nil {
+		return nil, syserr.TranslateNetstackError(err)
+	}
+
+	return New(t, linux.AF_PACKET, stype, protocol, wq, ep)
+}
+
 // Pair just returns nil sockets (not supported).
 func (*provider) Pair(*kernel.Task, linux.SockType, int) (*fs.File, *fs.File, *syserr.Error) {
 	return nil, nil, nil
 }
 
-// init registers socket providers for AF_INET and AF_INET6.
+// init registers socket providers for AF_INET, AF_INET6, and AF_PACKET.
 func init() {
 	// Providers backed by netstack.
 	p := []provider{
@@ -138,6 +184,9 @@ func init() {
 			family:   linux.AF_INET6,
 			netProto: ipv6.ProtocolNumber,
 		},
+		{
+			family: linux.AF_PACKET,
+		},
 	}
 
 	for i := range p {