netlink: allow to up/down interfaces via RTM_NEWLINK

It is required to run Docker in gVisor.
Netstack interfaces are always up, so this is no-op.

PiperOrigin-RevId: 576220175

pkg/sentry/socket/netlink/route/protocol.go

@@ -161,6 +161,72 @@ func (p *Protocol) getLink(ctx context.Context, msg *netlink.Message, ms *netlin
 	return nil
 }
 
+func (p *Protocol) newLink(ctx context.Context, msg *netlink.Message, ms *netlink.MessageSet) *syserr.Error {
+	stack := inet.StackFromContext(ctx)
+	if stack == nil {
+		// No network stack.
+		return syserr.ErrProtocolNotSupported
+	}
+
+	var ifinfomsg linux.InterfaceInfoMessage
+	attrs, ok := msg.GetData(&ifinfomsg)
+	if !ok {
+		return syserr.ErrInvalidArgument
+	}
+	for !attrs.Empty() {
+		// The index is unspecified, search by the interface name.
+		ahdr, value, rest, ok := attrs.ParseFirst()
+		if !ok {
+			return syserr.ErrInvalidArgument
+		}
+		attrs = rest
+		switch ahdr.Type {
+		case linux.IFLA_IFNAME:
+			if len(value) < 1 {
+				return syserr.ErrInvalidArgument
+			}
+			if ifinfomsg.Index != 0 {
+				// Device name changing isn't supported yet.
+				return syserr.ErrNotSupported
+			}
+			ifname := string(value[:len(value)-1])
+			for idx, ifa := range stack.Interfaces() {
+				if ifname == ifa.Name {
+					ifinfomsg.Index = idx
+					break
+				}
+			}
+		default:
+			ctx.Warningf("unexpected attribute: %x", ahdr.Type)
+			return syserr.ErrNotSupported
+		}
+	}
+	if ifinfomsg.Index == 0 {
+		return syserr.ErrNoDevice
+	}
+
+	flags := msg.Header().Flags
+	if flags&linux.NLM_F_EXCL != 0 {
+		return syserr.ErrExists
+	}
+	if flags&linux.NLM_F_REPLACE != 0 {
+		return syserr.ErrExists
+	}
+
+	if ifinfomsg.Flags != 0 || ifinfomsg.Change != 0 {
+		if ifinfomsg.Change & ^uint32(linux.IFF_UP) != 0 {
+			ctx.Warningf("Unsupported ifi_change flags: %x", ifinfomsg.Change)
+			return syserr.ErrInvalidArgument
+		}
+		if ifinfomsg.Flags & ^uint32(linux.IFF_UP) != 0 {
+			ctx.Warningf("Unsupported ifi_flags: %x", ifinfomsg.Change)
+			return syserr.ErrInvalidArgument
+		}
+		// Netstack interfaces are always up.
+	}
+	return nil
+}
+
 // delLink handles RTM_DELLINK requests.
 func (p *Protocol) delLink(ctx context.Context, msg *netlink.Message, ms *netlink.MessageSet) *syserr.Error {
 	stack := inet.StackFromContext(ctx)
@@ -576,6 +642,8 @@ func (p *Protocol) ProcessMessage(ctx context.Context, msg *netlink.Message, ms
 		}
 	} else if hdr.Flags&linux.NLM_F_REQUEST == linux.NLM_F_REQUEST {
 		switch hdr.Type {
+		case linux.RTM_NEWLINK:
+			return p.newLink(ctx, msg, ms)
 		case linux.RTM_GETLINK:
 			return p.getLink(ctx, msg, ms)
 		case linux.RTM_DELLINK:

test/syscalls/linux/socket_netlink_route.cc

@@ -198,6 +198,32 @@ TEST(NetlinkRouteTest, GetLinkByIndex) {
   EXPECT_TRUE(found) << "Netlink response does not contain any links.";
 }
 
+TEST(NetlinkRouteTest, LinkUp) {
+  SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(HaveCapability(CAP_NET_ADMIN)));
+  SKIP_IF(IsRunningWithHostinet());
+
+  Link loopback_link = ASSERT_NO_ERRNO_AND_VALUE(LoopbackLink());
+
+  FileDescriptor fd =
+      ASSERT_NO_ERRNO_AND_VALUE(NetlinkBoundSocket(NETLINK_ROUTE));
+
+  struct request {
+    struct nlmsghdr hdr;
+    struct ifinfomsg ifm;
+  };
+
+  struct request req = {};
+  req.hdr.nlmsg_len = sizeof(req);
+  req.hdr.nlmsg_type = RTM_NEWLINK;
+  req.hdr.nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
+  req.hdr.nlmsg_seq = kSeq;
+  req.ifm.ifi_family = AF_UNSPEC;
+  req.ifm.ifi_index = loopback_link.index;
+  req.ifm.ifi_change = IFF_UP;
+  req.ifm.ifi_flags = IFF_UP;
+  EXPECT_NO_ERRNO(NetlinkRequestAckOrError(fd, kSeq, &req, sizeof(req)));
+}
+
 TEST(NetlinkRouteTest, GetLinkByName) {
   Link loopback_link = ASSERT_NO_ERRNO_AND_VALUE(LoopbackLink());