Kernel: Add the SO_BINDTODEVICE socket option

This patch adds a way for a socket to ask to be routed through a
specific interface.
Currently, this option only applies to sending, however, it should also
apply to receiving...somehow :^)

Userland/test-bindtodevice.cpp

@@ -0,0 +1,131 @@
+#include <AK/Function.h>
+#include <AK/IPv4Address.h>
+#include <net/if.h>
+#include <netinet/in.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+
+void test_invalid(int);
+void test_no_route(int);
+void test_valid(int);
+void test_send(int);
+
+void test(AK::Function<void(int)> test_fn)
+{
+
+    int fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+    if (fd < 0) {
+        perror("socket");
+        return;
+    }
+
+    test_fn(fd);
+
+    // be a responsible boi
+    close(fd);
+}
+
+auto main() -> int
+{
+    test(test_invalid);
+    test(test_valid);
+    test(test_no_route);
+    test(test_send);
+}
+
+void test_invalid(int fd)
+{
+    // bind to an interface that does not exist
+    char buf[IFNAMSIZ];
+    socklen_t buflen = IFNAMSIZ;
+    memcpy(buf, "foodev", 7);
+
+    if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, buf, buflen) < 0) {
+        perror("setsockopt(SO_BINDTODEVICE) :: invalid (Should fail with ENODEV)");
+        puts("PASS invalid");
+    } else {
+        puts("FAIL invalid");
+    }
+}
+
+void test_valid(int fd)
+{
+    // bind to an interface that exists
+    char buf[IFNAMSIZ];
+    socklen_t buflen = IFNAMSIZ;
+    memcpy(buf, "loop0", 6);
+
+    if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, buf, buflen) < 0) {
+        perror("setsockopt(SO_BINDTODEVICE) :: valid");
+        puts("FAIL valid");
+    } else {
+        puts("PASS valid");
+    }
+}
+
+void test_no_route(int fd)
+{
+    // bind to an interface that cannot deliver
+    char buf[IFNAMSIZ];
+    socklen_t buflen = IFNAMSIZ;
+    memcpy(buf, "loop0", 6);
+
+    if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, buf, buflen) < 0) {
+        perror("setsockopt(SO_BINDTODEVICE) :: no_route");
+        puts("FAIL no_route");
+        return;
+    }
+    sockaddr_in sin;
+    memset(&sin, 0, sizeof(sin));
+
+    sin.sin_addr.s_addr = IPv4Address { 10, 0, 2, 15 }.to_u32();
+    sin.sin_port = 8080;
+    sin.sin_family = AF_INET;
+
+    if (bind(fd, (sockaddr*)&sin, sizeof(sin)) < 0) {
+        perror("bind() :: no_route");
+        puts("FAIL no_route");
+        return;
+    }
+
+    if (sendto(fd, "TEST", 4, 0, (sockaddr*)&sin, sizeof(sin)) < 0) {
+        perror("sendto() :: no_route (Should fail with EHOSTUNREACH)");
+        puts("PASS no_route");
+    } else
+        puts("FAIL no_route");
+}
+
+void test_send(int fd)
+{
+    // bind to an interface that cannot deliver
+    char buf[IFNAMSIZ];
+    socklen_t buflen = IFNAMSIZ;
+    memcpy(buf, "e1k0", 5);
+
+    if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, buf, buflen) < 0) {
+        perror("setsockopt(SO_BINDTODEVICE) :: send");
+        puts("FAIL send");
+        return;
+    }
+    sockaddr_in sin;
+    memset(&sin, 0, sizeof(sin));
+
+    sin.sin_addr.s_addr = IPv4Address { 10, 0, 2, 15 }.to_u32();
+    sin.sin_port = 8080;
+    sin.sin_family = AF_INET;
+
+    if (bind(fd, (sockaddr*)&sin, sizeof(sin)) < 0) {
+        perror("bind() :: send");
+        puts("FAIL send");
+        return;
+    }
+
+    if (sendto(fd, "TEST", 4, 0, (sockaddr*)&sin, sizeof(sin)) < 0) {
+        perror("sendto() :: send");
+        puts("FAIL send");
+        return;
+    }
+    puts("PASS send");
+}