unix: set ipv6 scope id for link-local addresses (#4107)

Link-local addresses (prefix fe80::/64) don't route unless you specify
the network interface to use so make libuv do that.

Fixes: https://github.com/nodejs/node/issues/48846

src/unix/tcp.c

@@ -27,6 +27,9 @@
 #include <assert.h>
 #include <errno.h>
 
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <ifaddrs.h>
 
 static int maybe_bind_socket(int fd) {
   union uv__sockaddr s;
@@ -198,11 +201,50 @@ int uv__tcp_bind(uv_tcp_t* tcp,
 }
 
 
+static int uv__is_ipv6_link_local(const struct sockaddr* addr) {
+  const struct sockaddr_in6* a6;
+  uint8_t b[2];
+
+  if (addr->sa_family != AF_INET6)
+    return 0;
+
+  a6 = (const struct sockaddr_in6*) addr;
+  memcpy(b, &a6->sin6_addr, sizeof(b));
+
+  return b[0] == 0xFE && b[1] == 0x80;
+}
+
+
+static int uv__ipv6_link_local_scope_id(void) {
+  struct sockaddr_in6* a6;
+  struct ifaddrs* ifa;
+  struct ifaddrs* p;
+  int rv;
+
+  if (getifaddrs(&ifa))
+    return 0;
+
+  for (p = ifa; p != NULL; p = p->ifa_next)
+    if (uv__is_ipv6_link_local(p->ifa_addr))
+      break;
+
+  rv = 0;
+  if (p != NULL) {
+    a6 = (struct sockaddr_in6*) p->ifa_addr;
+    rv = a6->sin6_scope_id;
+  }
+
+  freeifaddrs(ifa);
+  return rv;
+}
+
+
 int uv__tcp_connect(uv_connect_t* req,
                     uv_tcp_t* handle,
                     const struct sockaddr* addr,
                     unsigned int addrlen,
                     uv_connect_cb cb) {
+  struct sockaddr_in6 tmp6;
   int err;
   int r;
 
@@ -220,6 +262,14 @@ int uv__tcp_connect(uv_connect_t* req,
   if (err)
     return err;
 
+  if (uv__is_ipv6_link_local(addr)) {
+    memcpy(&tmp6, addr, sizeof(tmp6));
+    if (tmp6.sin6_scope_id == 0) {
+      tmp6.sin6_scope_id = uv__ipv6_link_local_scope_id();
+      addr = (void*) &tmp6;
+    }
+  }
+
   do {
     errno = 0;
     r = connect(uv__stream_fd(handle), addr, addrlen);

test/test-list.h

@@ -128,6 +128,7 @@ TEST_DECLARE   (tcp_bind_or_listen_error_after_close)
 TEST_DECLARE   (tcp_listen_without_bind)
 TEST_DECLARE   (tcp_connect_error_fault)
 TEST_DECLARE   (tcp_connect6_error_fault)
+TEST_DECLARE   (tcp_connect6_link_local)
 TEST_DECLARE   (tcp_connect_timeout)
 TEST_DECLARE   (tcp_local_connect_timeout)
 TEST_DECLARE   (tcp6_local_connect_timeout)
@@ -727,6 +728,7 @@ TASK_LIST_START
   TEST_ENTRY  (tcp_listen_without_bind)
   TEST_ENTRY  (tcp_connect_error_fault)
   TEST_ENTRY  (tcp_connect6_error_fault)
+  TEST_ENTRY  (tcp_connect6_link_local)
   TEST_ENTRY  (tcp_connect_timeout)
   TEST_ENTRY  (tcp_local_connect_timeout)
   TEST_ENTRY  (tcp6_local_connect_timeout)

test/test-tcp-connect6-error.c

@@ -69,3 +69,38 @@ TEST_IMPL(tcp_connect6_error_fault) {
   MAKE_VALGRIND_HAPPY(uv_default_loop());
   return 0;
 }
+
+
+TEST_IMPL(tcp_connect6_link_local) {
+  struct sockaddr_in6 addr;
+  uv_connect_t req;
+  uv_tcp_t server;
+
+#if defined(__QEMU__)
+  /* qemu's sockaddr_in6 translation is broken pre-qemu 8.0.0
+   * when host endianness != guest endiannes.
+   * Fixed in https://github.com/qemu/qemu/commit/44cf6731d6b.
+   */
+  RETURN_SKIP("Test does not currently work in QEMU");
+#endif  /* defined(__QEMU__) */
+
+  ASSERT_OK(uv_ip6_addr("fe80::0bad:babe", 1337, &addr));
+  ASSERT_OK(uv_tcp_init(uv_default_loop(), &server));
+
+  /* We're making two shaky assumptions here:
+   * 1. There is a network interface that routes IPv6 link-local traffic, and
+   * 2. There is no firewall rule that blackholes or otherwise hard-kills the
+   *    connection attempt to the address above, i.e., we don't expect the
+   *    connect() system call to fail synchronously.
+   */
+  ASSERT_OK(uv_tcp_connect(&req,
+                           &server,
+                           (struct sockaddr*) &addr,
+                           connect_cb));
+
+  uv_close((uv_handle_t*) &server, NULL);
+  ASSERT_OK(uv_run(uv_default_loop(), UV_RUN_DEFAULT));
+
+  MAKE_VALGRIND_HAPPY(uv_default_loop());
+  return 0;
+}