Basic support for ip link/addr and ifconfig

Closes #94

PiperOrigin-RevId: 207997580
Change-Id: I19b426f1586b5ec12f8b0cd5884d5b401d334924

10 files changed, 135 insertions, 62 deletions

diff --git a/pkg/abi/linux/netlink_route.go b/pkg/abi/linux/netlink_route.go
index 0d88bc5c5..a5d778748 100644
--- a/pkg/abi/linux/netlink_route.go
+++ b/pkg/abi/linux/netlink_route.go
@@ -184,3 +184,8 @@ const (
 	IFA_MULTICAST = 7
 	IFA_FLAGS     = 8
 )
+
+// Device types, from uapi/linux/if_arp.h.
+const (
+	ARPHRD_LOOPBACK = 772
+)
diff --git a/pkg/sentry/inet/inet.go b/pkg/sentry/inet/inet.go
index e54a61196..30ca4e0c0 100644
--- a/pkg/sentry/inet/inet.go
+++ b/pkg/sentry/inet/inet.go
@@ -67,6 +67,9 @@ type Interface struct {
 
 	// Addr is the hardware device address.
 	Addr []byte
+
+	// MTU is the maximum transmission unit.
+	MTU uint32
 }
 
 // InterfaceAddr contains information about a network interface address.
diff --git a/pkg/sentry/socket/epsocket/epsocket.go b/pkg/sentry/socket/epsocket/epsocket.go
index f969a1d7c..b32eda96f 100644
--- a/pkg/sentry/socket/epsocket/epsocket.go
+++ b/pkg/sentry/socket/epsocket/epsocket.go
@@ -48,7 +48,7 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/syserror"
 	"gvisor.googlesource.com/gvisor/pkg/tcpip"
 	"gvisor.googlesource.com/gvisor/pkg/tcpip/buffer"
-	nstack "gvisor.googlesource.com/gvisor/pkg/tcpip/stack"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/stack"
 	"gvisor.googlesource.com/gvisor/pkg/tcpip/transport/unix"
 	"gvisor.googlesource.com/gvisor/pkg/waiter"
 )
@@ -452,7 +452,7 @@ func (s *SocketOperations) GetSockOpt(t *kernel.Task, level, name, outLen int) (
 // sockets backed by a commonEndpoint.
 func GetSockOpt(t *kernel.Task, s socket.Socket, ep commonEndpoint, family int, skType unix.SockType, level, name, outLen int) (interface{}, *syserr.Error) {
 	switch level {
-	case syscall.SOL_SOCKET:
+	case linux.SOL_SOCKET:
 		switch name {
 		case linux.SO_TYPE:
 			if outLen < sizeOfInt32 {
@@ -634,7 +634,7 @@ func (s *SocketOperations) SetSockOpt(t *kernel.Task, level int, name int, optVa
 // sockets backed by a commonEndpoint.
 func SetSockOpt(t *kernel.Task, s socket.Socket, ep commonEndpoint, level int, name int, optVal []byte) *syserr.Error {
 	switch level {
-	case syscall.SOL_SOCKET:
+	case linux.SOL_SOCKET:
 		switch name {
 		case linux.SO_SNDBUF:
 			if len(optVal) < sizeOfInt32 {
@@ -1191,7 +1191,9 @@ func interfaceIoctl(ctx context.Context, io usermem.IO, arg int, ifr *linux.IFRe
 		if err != nil {
 			return err
 		}
-		usermem.ByteOrder.PutUint16(ifr.Data[:2], f)
+		// Drop the flags that don't fit in the size that we need to return. This
+		// matches Linux behavior.
+		usermem.ByteOrder.PutUint16(ifr.Data[:2], uint16(f))
 
 	case syscall.SIOCGIFADDR:
 		// Copy the IPv4 address out.
@@ -1304,7 +1306,7 @@ func ifconfIoctl(ctx context.Context, io usermem.IO, ifc *linux.IFConf) error {
 // interfaceStatusFlags returns status flags for an interface in the stack.
 // Flag values and meanings are described in greater detail in netdevice(7) in
 // the SIOCGIFFLAGS section.
-func interfaceStatusFlags(stack inet.Stack, name string) (uint16, *syserr.Error) {
+func interfaceStatusFlags(stack inet.Stack, name string) (uint32, *syserr.Error) {
 	// epsocket should only ever be passed an epsocket.Stack.
 	epstack, ok := stack.(*Stack)
 	if !ok {
@@ -1312,37 +1314,27 @@ func interfaceStatusFlags(stack inet.Stack, name string) (uint16, *syserr.Error)
 	}
 
 	// Find the NIC corresponding to this interface.
-	var (
-		nicid tcpip.NICID
-		info  nstack.NICInfo
-		found bool
-	)
-	ns := epstack.Stack
-	for nicid, info = range ns.NICInfo() {
+	for _, info := range epstack.Stack.NICInfo() {
 		if info.Name == name {
-			found = true
-			break
+			return nicStateFlagsToLinux(info.Flags), nil
 		}
 	}
-	if !found {
-		return 0, syserr.ErrNoDevice
-	}
+	return 0, syserr.ErrNoDevice
+}
 
-	// Set flags based on NIC state.
-	nicFlags, err := ns.NICFlags(nicid)
-	if err != nil {
-		return 0, syserr.TranslateNetstackError(err)
+func nicStateFlagsToLinux(f stack.NICStateFlags) uint32 {
+	var rv uint32
+	if f.Up {
+		rv |= linux.IFF_UP | linux.IFF_LOWER_UP
 	}
-
-	var retFlags uint16
-	if nicFlags.Up {
-		retFlags |= linux.IFF_UP
+	if f.Running {
+		rv |= linux.IFF_RUNNING
 	}
-	if nicFlags.Running {
-		retFlags |= linux.IFF_RUNNING
+	if f.Promiscuous {
+		rv |= linux.IFF_PROMISC
 	}
-	if nicFlags.Promiscuous {
-		retFlags |= linux.IFF_PROMISC
+	if f.Loopback {
+		rv |= linux.IFF_LOOPBACK
 	}
-	return retFlags, nil
+	return rv
 }
diff --git a/pkg/sentry/socket/epsocket/stack.go b/pkg/sentry/socket/epsocket/stack.go
index 12b4b4767..e4ed52fc8 100644
--- a/pkg/sentry/socket/epsocket/stack.go
+++ b/pkg/sentry/socket/epsocket/stack.go
@@ -41,10 +41,16 @@ func (s *Stack) SupportsIPv6() bool {
 func (s *Stack) Interfaces() map[int32]inet.Interface {
 	is := make(map[int32]inet.Interface)
 	for id, ni := range s.Stack.NICInfo() {
+		var devType uint16
+		if ni.Flags.Loopback {
+			devType = linux.ARPHRD_LOOPBACK
+		}
 		is[int32(id)] = inet.Interface{
-			Name: ni.Name,
-			Addr: []byte(ni.LinkAddress),
-			// TODO: Other fields.
+			Name:       ni.Name,
+			Addr:       []byte(ni.LinkAddress),
+			Flags:      uint32(nicStateFlagsToLinux(ni.Flags)),
+			DeviceType: devType,
+			MTU:        ni.MTU,
 		}
 	}
 	return is
diff --git a/pkg/sentry/socket/netlink/route/protocol.go b/pkg/sentry/socket/netlink/route/protocol.go
index 55a76e916..70322b9ed 100644
--- a/pkg/sentry/socket/netlink/route/protocol.go
+++ b/pkg/sentry/socket/netlink/route/protocol.go
@@ -16,6 +16,8 @@
 package route
 
 import (
+	"bytes"
+
 	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/inet"
@@ -97,9 +99,18 @@ func (p *Protocol) dumpLinks(ctx context.Context, hdr linux.NetlinkMessageHeader
 		})
 
 		m.PutAttrString(linux.IFLA_IFNAME, i.Name)
+		m.PutAttr(linux.IFLA_MTU, i.MTU)
+
+		mac := make([]byte, 6)
+		brd := mac
+		if len(i.Addr) > 0 {
+			mac = i.Addr
+			brd = bytes.Repeat([]byte{0xff}, len(i.Addr))
+		}
+		m.PutAttr(linux.IFLA_ADDRESS, mac)
+		m.PutAttr(linux.IFLA_BROADCAST, brd)
 
-		// TODO: There are many more attributes, such as
-		// MAC address.
+		// TODO: There are many more attributes.
 	}
 
 	return nil
diff --git a/pkg/sentry/socket/netlink/socket.go b/pkg/sentry/socket/netlink/socket.go
index e15d1546c..f3b2c7256 100644
--- a/pkg/sentry/socket/netlink/socket.go
+++ b/pkg/sentry/socket/netlink/socket.go
@@ -16,6 +16,7 @@
 package netlink
 
 import (
+	"math"
 	"sync"
 
 	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
@@ -39,8 +40,18 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/waiter"
 )
 
-// defaultSendBufferSize is the default size for the send buffer.
-const defaultSendBufferSize = 16 * 1024
+const sizeOfInt32 int = 4
+
+const (
+	// minBufferSize is the smallest size of a send buffer.
+	minSendBufferSize = 4 << 10 // 4096 bytes.
+
+	// defaultSendBufferSize is the default size for the send buffer.
+	defaultSendBufferSize = 16 * 1024
+
+	// maxBufferSize is the largest size a send buffer can grow to.
+	maxSendBufferSize = 4 << 20 // 4MB
+)
 
 // netlinkSocketDevice is the netlink socket virtual device.
 var netlinkSocketDevice = device.NewAnonDevice()
@@ -86,7 +97,7 @@ type Socket struct {
 
 	// sendBufferSize is the send buffer "size". We don't actually have a
 	// fixed buffer but only consume this many bytes.
-	sendBufferSize uint64
+	sendBufferSize uint32
 }
 
 var _ socket.Socket = (*Socket)(nil)
@@ -273,13 +284,54 @@ func (s *Socket) Shutdown(t *kernel.Task, how int) *syserr.Error {
 
 // GetSockOpt implements socket.Socket.GetSockOpt.
 func (s *Socket) GetSockOpt(t *kernel.Task, level int, name int, outLen int) (interface{}, *syserr.Error) {
-	// TODO: no sockopts supported.
+	switch level {
+	case linux.SOL_SOCKET:
+		switch name {
+		case linux.SO_SNDBUF:
+			if outLen < sizeOfInt32 {
+				return nil, syserr.ErrInvalidArgument
+			}
+			return int32(s.sendBufferSize), nil
+
+		case linux.SO_RCVBUF:
+			if outLen < sizeOfInt32 {
+				return nil, syserr.ErrInvalidArgument
+			}
+			// We don't have limit on receiving size.
+			return math.MaxInt32, nil
+		}
+	}
+	// TODO: other sockopts are not supported.
 	return nil, syserr.ErrProtocolNotAvailable
 }
 
 // SetSockOpt implements socket.Socket.SetSockOpt.
 func (s *Socket) SetSockOpt(t *kernel.Task, level int, name int, opt []byte) *syserr.Error {
-	// TODO: no sockopts supported.
+	switch level {
+	case linux.SOL_SOCKET:
+		switch name {
+		case linux.SO_SNDBUF:
+			if len(opt) < sizeOfInt32 {
+				return syserr.ErrInvalidArgument
+			}
+			size := usermem.ByteOrder.Uint32(opt)
+			if size < minSendBufferSize {
+				size = minSendBufferSize
+			} else if size > maxSendBufferSize {
+				size = maxSendBufferSize
+			}
+			s.sendBufferSize = size
+			return nil
+		case linux.SO_RCVBUF:
+			if len(opt) < sizeOfInt32 {
+				return syserr.ErrInvalidArgument
+			}
+			// We don't have limit on receiving size. So just accept anything as
+			// valid for compatibility.
+			return nil
+		}
+	}
+	// TODO: other sockopts are not supported.
 	return syserr.ErrProtocolNotAvailable
 }
 
@@ -489,7 +541,7 @@ func (s *Socket) sendMsg(ctx context.Context, src usermem.IOSequence, to []byte,
 
 	// For simplicity, and consistency with Linux, we copy in the entire
 	// message up front.
-	if uint64(src.NumBytes()) > s.sendBufferSize {
+	if src.NumBytes() > int64(s.sendBufferSize) {
 		return 0, syserr.ErrMessageTooLong
 	}
 
diff --git a/pkg/tcpip/link/loopback/loopback.go b/pkg/tcpip/link/loopback/loopback.go
index b4dc4833c..015275721 100644
--- a/pkg/tcpip/link/loopback/loopback.go
+++ b/pkg/tcpip/link/loopback/loopback.go
@@ -56,7 +56,7 @@ func (*endpoint) MTU() uint32 {
 // Capabilities implements stack.LinkEndpoint.Capabilities. Loopback advertises
 // itself as supporting checksum offload, but in reality it's just omitted.
 func (*endpoint) Capabilities() stack.LinkEndpointCapabilities {
-	return stack.CapabilityChecksumOffload | stack.CapabilitySaveRestore
+	return stack.CapabilityChecksumOffload | stack.CapabilitySaveRestore | stack.CapabilityLoopback
 }
 
 // MaxHeaderLength implements stack.LinkEndpoint.MaxHeaderLength. Given that the
diff --git a/pkg/tcpip/stack/nic.go b/pkg/tcpip/stack/nic.go
index c1480f97b..592006a32 100644
--- a/pkg/tcpip/stack/nic.go
+++ b/pkg/tcpip/stack/nic.go
@@ -67,6 +67,13 @@ func (n *NIC) setPromiscuousMode(enable bool) {
 	n.mu.Unlock()
 }
 
+func (n *NIC) isPromiscuousMode() bool {
+	n.mu.RLock()
+	rv := n.promiscuous
+	n.mu.RUnlock()
+	return rv
+}
+
 // setSpoofing enables or disables address spoofing.
 func (n *NIC) setSpoofing(enable bool) {
 	n.mu.Lock()
diff --git a/pkg/tcpip/stack/registration.go b/pkg/tcpip/stack/registration.go
index 01a29689d..bbe887144 100644
--- a/pkg/tcpip/stack/registration.go
+++ b/pkg/tcpip/stack/registration.go
@@ -205,6 +205,7 @@ const (
 	CapabilityResolutionRequired
 	CapabilitySaveRestore
 	CapabilityDisconnectOk
+	CapabilityLoopback
 )
 
 // LinkEndpoint is the interface implemented by data link layer protocols (e.g.,
diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index 6c4aa7cc5..e2b9dc2c0 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -563,6 +563,12 @@ type NICInfo struct {
 	Name              string
 	LinkAddress       tcpip.LinkAddress
 	ProtocolAddresses []tcpip.ProtocolAddress
+
+	// Flags indicate the state of the NIC.
+	Flags NICStateFlags
+
+	// MTU is the maximum transmission unit.
+	MTU uint32
 }
 
 // NICInfo returns a map of NICIDs to their associated information.
@@ -572,10 +578,18 @@ func (s *Stack) NICInfo() map[tcpip.NICID]NICInfo {
 
 	nics := make(map[tcpip.NICID]NICInfo)
 	for id, nic := range s.nics {
+		flags := NICStateFlags{
+			Up:          true, // Netstack interfaces are always up.
+			Running:     nic.linkEP.IsAttached(),
+			Promiscuous: nic.isPromiscuousMode(),
+			Loopback:    nic.linkEP.Capabilities()&CapabilityLoopback != 0,
+		}
 		nics[id] = NICInfo{
 			Name:              nic.name,
 			LinkAddress:       nic.linkEP.LinkAddress(),
 			ProtocolAddresses: nic.Addresses(),
+			Flags:             flags,
+			MTU:               nic.linkEP.MTU(),
 		}
 	}
 	return nics
@@ -591,27 +605,9 @@ type NICStateFlags struct {
 
 	// Promiscuous indicates whether the interface is in promiscuous mode.
 	Promiscuous bool
-}
-
-// NICFlags returns flags about the state of the NIC. It returns an error if
-// the NIC corresponding to id cannot be found.
-func (s *Stack) NICFlags(id tcpip.NICID) (NICStateFlags, *tcpip.Error) {
-	s.mu.RLock()
-	defer s.mu.RUnlock()
 
-	nic := s.nics[id]
-	if nic == nil {
-		return NICStateFlags{}, tcpip.ErrUnknownNICID
-	}
-
-	ret := NICStateFlags{
-		// Netstack interfaces are always up.
-		Up: true,
-
-		Running:     nic.linkEP.IsAttached(),
-		Promiscuous: nic.promiscuous,
-	}
-	return ret, nil
+	// Loopback indicates whether the interface is a loopback.
+	Loopback bool
 }
 
 // AddAddress adds a new network-layer address to the specified NIC.