support /proc/net/route

This proc file reports routing information to applications inside the
container.

Signed-off-by: Jianfeng Tan <henry.tjf@antfin.com>
Change-Id: I498e47f8c4c185419befbb42d849d0b099ec71f3

pkg/abi/linux/netlink_route.go

@@ -325,3 +325,9 @@ const (
 	RTA_SPORT         = 28
 	RTA_DPORT         = 29
 )
+
+// Route flags, from include/uapi/linux/route.h.
+const (
+	RTF_GATEWAY = 0x2
+	RTF_UP      = 0x1
+)

pkg/sentry/fs/proc/BUILD

@@ -53,6 +53,7 @@ go_library(
         "//pkg/sentry/usage",
         "//pkg/sentry/usermem",
         "//pkg/syserror",
+        "//pkg/tcpip/header",
         "//pkg/waiter",
     ],
 )

pkg/sentry/fs/proc/net.go

@@ -35,6 +35,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
 	"gvisor.dev/gvisor/pkg/sentry/usermem"
 	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/tcpip/header"
 )
 
 // newNet creates a new proc net entry.
@@ -60,7 +61,7 @@ func (p *proc) newNetDir(ctx context.Context, k *kernel.Kernel, msrc *fs.MountSo
 			// (ClockGetres returns 1ns resolution).
 			"psched": newStaticProcInode(ctx, msrc, []byte(fmt.Sprintf("%08x %08x %08x %08x\n", uint64(time.Microsecond/time.Nanosecond), 64, 1000000, uint64(time.Second/time.Nanosecond)))),
 			"ptype":  newStaticProcInode(ctx, msrc, []byte("Type Device      Function")),
-			"route":  newStaticProcInode(ctx, msrc, []byte("Iface   Destination     Gateway         Flags   RefCnt  Use     Metric  Mask            MTU     Window  IRTT")),
+			"route":  seqfile.NewSeqFileInode(ctx, &netRoute{s: s}, msrc),
 			"tcp":    seqfile.NewSeqFileInode(ctx, &netTCP{k: k}, msrc),
 			"udp":    seqfile.NewSeqFileInode(ctx, &netUDP{k: k}, msrc),
 			"unix":   seqfile.NewSeqFileInode(ctx, &netUnix{k: k}, msrc),
@@ -310,6 +311,81 @@ func (n *netSnmp) ReadSeqFileData(ctx context.Context, h seqfile.SeqHandle) ([]s
 	return data, 0
 }
 
+// netRoute implements seqfile.SeqSource for /proc/net/route.
+//
+// +stateify savable
+type netRoute struct {
+	s inet.Stack
+}
+
+// NeedsUpdate implements seqfile.SeqSource.NeedsUpdate.
+func (n *netRoute) NeedsUpdate(generation int64) bool {
+	return true
+}
+
+// ReadSeqFileData implements seqfile.SeqSource.ReadSeqFileData.
+// See Linux's net/ipv4/fib_trie.c:fib_route_seq_show.
+func (n *netRoute) ReadSeqFileData(ctx context.Context, h seqfile.SeqHandle) ([]seqfile.SeqData, int64) {
+	if h != nil {
+		return nil, 0
+	}
+
+	interfaces := n.s.Interfaces()
+	contents := []string{"Iface\tDestination\tGateway\tFlags\tRefCnt\tUse\tMetric\tMask\tMTU\tWindow\tIRTT"}
+	for _, rt := range n.s.RouteTable() {
+		// /proc/net/route only includes ipv4 routes.
+		if rt.Family != linux.AF_INET {
+			continue
+		}
+
+		// /proc/net/route does not include broadcast or multicast routes.
+		if rt.Type == linux.RTN_BROADCAST || rt.Type == linux.RTN_MULTICAST {
+			continue
+		}
+
+		iface, ok := interfaces[rt.OutputInterface]
+		if !ok || iface.Name == "lo" {
+			continue
+		}
+
+		var (
+			gw     uint32
+			prefix uint32
+			flags  = linux.RTF_UP
+		)
+		if len(rt.GatewayAddr) == header.IPv4AddressSize {
+			flags |= linux.RTF_GATEWAY
+			gw = usermem.ByteOrder.Uint32(rt.GatewayAddr)
+		}
+		if len(rt.DstAddr) == header.IPv4AddressSize {
+			prefix = usermem.ByteOrder.Uint32(rt.DstAddr)
+		}
+		l := fmt.Sprintf(
+			"%s\t%08X\t%08X\t%04X\t%d\t%d\t%d\t%08X\t%d\t%d\t%d",
+			iface.Name,
+			prefix,
+			gw,
+			flags,
+			0, // RefCnt.
+			0, // Use.
+			0, // Metric.
+			(uint32(1)<<rt.DstLen)-1,
+			0, // MTU.
+			0, // Window.
+			0, // RTT.
+		)
+		contents = append(contents, l)
+	}
+
+	var data []seqfile.SeqData
+	for _, l := range contents {
+		l = fmt.Sprintf("%-127s\n", l)
+		data = append(data, seqfile.SeqData{Buf: []byte(l), Handle: (*netRoute)(nil)})
+	}
+
+	return data, 0
+}
+
 // netUnix implements seqfile.SeqSource for /proc/net/unix.
 //
 // +stateify savable