Kernel+Utilities: Add the route utility

This exposes the global routing table in the /proc directory and adds
the userspace utility to query dynamically add from the table.

Userland/Utilities/route.cpp

@@ -0,0 +1,190 @@
+/*
+ * Copyright (c) 2022, Brandon Pruitt <brapru@pm.me>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/IPv4Address.h>
+#include <AK/JsonArray.h>
+#include <AK/JsonObject.h>
+#include <AK/QuickSort.h>
+#include <AK/String.h>
+#include <AK/StringView.h>
+#include <LibCore/ArgsParser.h>
+#include <LibCore/File.h>
+#include <LibCore/ProcessStatisticsReader.h>
+#include <LibCore/System.h>
+#include <LibMain/Main.h>
+#include <net/if.h>
+#include <net/route.h>
+#include <netinet/in.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+ErrorOr<int> serenity_main(Main::Arguments arguments)
+{
+    TRY(Core::System::pledge("stdio rpath inet"));
+    TRY(Core::System::unveil("/proc/net", "r"));
+    TRY(Core::System::unveil(nullptr, nullptr));
+
+    StringView modify_action;
+    StringView value_host_address;
+    StringView value_network_address;
+    StringView value_gateway_address;
+    StringView value_netmask_address;
+    StringView value_interface;
+
+    Core::ArgsParser args_parser;
+    args_parser.set_general_help("Display kernel routing table");
+    args_parser.add_positional_argument(modify_action, "Modify the global routing table { add | del }", "action", Core::ArgsParser::Required::No);
+    args_parser.add_option(value_host_address, "Target destination is an IPv4 address", "host", 'h', "host");
+    args_parser.add_option(value_network_address, "Target destination is a network address", "net", 'n', "net");
+    args_parser.add_option(value_gateway_address, "Route packets via a gateway", "gw", 'g', "gw");
+    args_parser.add_option(value_netmask_address, "The netmask to be used when adding a network route", "netmask", 'm', "netmask");
+    args_parser.add_option(value_interface, "Force the route to be associated with the specified device interface", "interface", 'i', "interface");
+    args_parser.parse(arguments);
+
+    enum class Alignment {
+        Left,
+        Right
+    };
+
+    struct Column {
+        String title;
+        Alignment alignment { Alignment::Left };
+        int width { 0 };
+        String buffer;
+    };
+
+    Vector<Column> columns;
+
+    int destination_column = -1;
+    int gateway_column = -1;
+    int genmask_column = -1;
+    int interface_column = -1;
+
+    auto add_column = [&](auto title, auto alignment, auto width) {
+        columns.append({ title, alignment, width, {} });
+        return columns.size() - 1;
+    };
+
+    destination_column = add_column("Destination", Alignment::Left, 15);
+    gateway_column = add_column("Gateway", Alignment::Left, 15);
+    genmask_column = add_column("Genmask", Alignment::Left, 15);
+    interface_column = add_column("Interface", Alignment::Left, 9);
+
+    auto print_column = [](auto& column, auto& string) {
+        if (!column.width) {
+            out("{}", string);
+            return;
+        }
+        if (column.alignment == Alignment::Right) {
+            out("{:>{1}}  "sv, string, column.width);
+        } else {
+            out("{:<{1}}  "sv, string, column.width);
+        }
+    };
+
+    if (modify_action.is_empty()) {
+        auto file = TRY(Core::File::open("/proc/net/route", Core::OpenMode::ReadOnly));
+        auto file_contents = file->read_all();
+        auto json = TRY(JsonValue::from_string(file_contents));
+
+        outln("Kernel IP routing table");
+
+        for (auto& column : columns)
+            print_column(column, column.title);
+        outln();
+
+        Vector<JsonValue> sorted_regions = json.as_array().values();
+        quick_sort(sorted_regions, [](auto& a, auto& b) {
+            return a.as_object().get("destination").to_string() < b.as_object().get("destination").to_string();
+        });
+
+        for (auto& value : sorted_regions) {
+            auto& if_object = value.as_object();
+
+            auto destination = if_object.get("destination").to_string();
+            auto gateway = if_object.get("gateway").to_string();
+            auto genmask = if_object.get("genmask").to_string();
+            auto interface = if_object.get("interface").to_string();
+
+            if (destination_column != -1)
+                columns[destination_column].buffer = destination;
+            if (gateway_column != -1)
+                columns[gateway_column].buffer = gateway;
+            if (genmask_column != -1)
+                columns[genmask_column].buffer = genmask;
+            if (interface_column != -1)
+                columns[interface_column].buffer = interface;
+
+            for (auto& column : columns)
+                print_column(column, column.buffer);
+            outln();
+        };
+    }
+
+    if (!modify_action.is_empty()) {
+        bool const action_add = (modify_action == "add");
+        bool const action_del = (modify_action == "del");
+
+        if (!action_add && !action_del) {
+            warnln("Invalid modify action: {}", modify_action);
+            return 1;
+        }
+
+        if (value_host_address.is_empty() && value_network_address.is_empty()) {
+            warnln("No target host or network specified");
+            return 1;
+        }
+
+        Optional<IPv4Address> destination;
+
+        if (!value_host_address.is_empty())
+            destination = AK::IPv4Address::from_string(value_host_address);
+
+        if (!value_network_address.is_empty())
+            destination = AK::IPv4Address::from_string(value_network_address);
+
+        if (!destination.has_value()) {
+            warnln("Invalid destination IPv4 address");
+            return 1;
+        }
+
+        auto gateway = AK::IPv4Address::from_string(value_gateway_address);
+        if (!gateway.has_value()) {
+            warnln("Invalid gateway IPv4 address: '{}'", value_gateway_address);
+            return 1;
+        }
+
+        auto genmask = AK::IPv4Address::from_string(value_netmask_address);
+        if (!genmask.has_value()) {
+            warnln("Invalid genmask IPv4 address: '{}'", value_netmask_address);
+            return 1;
+        }
+
+        int fd = TRY(Core::System::socket(AF_INET, SOCK_DGRAM, IPPROTO_IP));
+
+        rtentry rt {};
+        memset(&rt, 0, sizeof(rt));
+
+        rt.rt_dev = const_cast<char*>(value_interface.characters_without_null_termination());
+        rt.rt_gateway.sa_family = AF_INET;
+        ((sockaddr_in&)rt.rt_dst).sin_addr.s_addr = destination.value().to_in_addr_t();
+        ((sockaddr_in&)rt.rt_gateway).sin_addr.s_addr = gateway.value().to_in_addr_t();
+        ((sockaddr_in&)rt.rt_genmask).sin_addr.s_addr = genmask.value().to_in_addr_t();
+        rt.rt_flags = RTF_UP | RTF_GATEWAY;
+
+        if (action_add)
+            TRY(Core::System::ioctl(fd, SIOCADDRT, &rt));
+
+        // FIXME: Add support for route deletion.
+        if (action_del) {
+            warnln("Route deletion currently not implemented.");
+            return 1;
+        }
+    }
+
+    return 0;
+}