Utilities: Support static assignment of the ARP table

Kernel/Net/NetworkTask.cpp

@@ -150,7 +150,6 @@ void handle_arp(const EthernetFrameHeader& eth, size_t frame_size)
     if (!packet.sender_hardware_address().is_zero() && !packet.sender_protocol_address().is_zero()) {
         // Someone has this IPv4 address. I guess we can try to remember that.
         // FIXME: Protect against ARP spamming.
-        // FIXME: Support static ARP table entries.
         update_arp_table(packet.sender_protocol_address(), packet.sender_hardware_address(), UpdateArp::Set);
     }
 

Userland/Utilities/arp.cpp

@@ -6,29 +6,98 @@
 
 #include <AK/Assertions.h>
 #include <AK/ByteBuffer.h>
+#include <AK/IPv4Address.h>
 #include <AK/JsonObject.h>
+#include <AK/MACAddress.h>
+#include <AK/String.h>
+#include <AK/Types.h>
+#include <LibCore/ArgsParser.h>
 #include <LibCore/File.h>
+#include <net/if.h>
+#include <net/route.h>
+#include <netinet/in.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
 
-int main()
+int main(int argc, char** argv)
 {
+    static bool flag_set;
+    static bool flag_delete;
+    const char* value_ipv4_address = nullptr;
+    const char* value_hw_address = nullptr;
+
+    Core::ArgsParser args_parser;
+    args_parser.set_general_help("Display or modify the system ARP cache");
+    args_parser.add_option(flag_set, "Set an ARP table entry", "set", 's');
+    args_parser.add_option(flag_delete, "Delete an ARP table entry", "delete", 'd');
+    args_parser.add_positional_argument(value_ipv4_address, "IPv4 protocol address", "address", Core::ArgsParser::Required::No);
+    args_parser.add_positional_argument(value_hw_address, "Hardware address", "hwaddress", Core::ArgsParser::Required::No);
+    args_parser.parse(argc, argv);
+
     auto file = Core::File::construct("/proc/net/arp");
     if (!file->open(Core::OpenMode::ReadOnly)) {
         warnln("Failed to open {}: {}", file->name(), file->error_string());
         return 1;
     }
 
-    outln("Address          HWaddress");
-    auto file_contents = file->read_all();
-    auto json = JsonValue::from_string(file_contents);
-    VERIFY(json.has_value());
-    json.value().as_array().for_each([](auto& value) {
-        auto& if_object = value.as_object();
+    if (!flag_set && !flag_delete) {
+        outln("Address          HWaddress");
+        auto file_contents = file->read_all();
+        auto json = JsonValue::from_string(file_contents);
+        VERIFY(json.has_value());
+        json.value().as_array().for_each([](auto& value) {
+            auto& if_object = value.as_object();
+
+            auto ip_address = if_object.get("ip_address").to_string();
+            auto mac_address = if_object.get("mac_address").to_string();
+
+            outln("{:15}  {:17}", ip_address, mac_address);
+        });
+    }
+
+    if (flag_set || flag_delete) {
+        if (!value_ipv4_address || !value_hw_address) {
+            warnln("No protocol address or hardware address specified.");
+            return 1;
+        }
+
+        auto address = IPv4Address::from_string(value_ipv4_address);
+        if (!address.has_value()) {
+            warnln("Invalid IPv4 protocol address: '{}'", value_ipv4_address);
+            return 1;
+        }
 
-        auto ip_address = if_object.get("ip_address").to_string();
-        auto mac_address = if_object.get("mac_address").to_string();
+        auto hw_address = MACAddress::from_string(value_hw_address);
+        if (!hw_address.has_value()) {
+            warnln("Invalid MACAddress: '{}'", value_hw_address);
+            return 1;
+        }
 
-        outln("{:15}  {:17}", ip_address, mac_address);
-    });
+        int fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP);
+        if (fd < 0) {
+            perror("socket");
+            return 1;
+        }
+
+        struct arpreq arp_req;
+        memset(&arp_req, 0, sizeof(arp_req));
+
+        arp_req.arp_pa.sa_family = AF_INET;
+        ((sockaddr_in&)arp_req.arp_pa).sin_addr.s_addr = address.value().to_in_addr_t();
+
+        *(MACAddress*)&arp_req.arp_ha.sa_data[0] = hw_address.value();
+
+        int rc;
+        if (flag_set)
+            rc = ioctl(fd, SIOCSARP, &arp_req);
+        if (flag_delete)
+            rc = ioctl(fd, SIOCDARP, &arp_req);
+
+        if (rc < 0) {
+            perror("ioctl");
+            return 1;
+        }
+    }
 
     return 0;
 }