linux: support abstract unix socket autobinding (libuv#4499)

Autobinding is a feature that lets the kernel pick a name for the
abstract socket, instead of userspace having to provide one.

Two bugs that this change exposed are also fixed:

1. strlen(sa.sun_path) can read past the end if the file path is exactly
   sizeof(sa.sun_path) long (use memchr instead), and

2. don't return UV_ENOBUFS for abstract sockets when the buffer is
   exactly large enough to hold the result; per commit e5f4b79,
   abstract socket names are not zero-terminated

src/unix/pipe.c

@@ -76,8 +76,13 @@ int uv_pipe_bind2(uv_pipe_t* handle,
   if (name == NULL)
     return UV_EINVAL;
 
+  /* namelen==0 on Linux means autobind the listen socket in the abstract
+   * socket namespace, see `man 7 unix` for details.
+   */
+#if !defined(__linux__)
   if (namelen == 0)
     return UV_EINVAL;
+#endif
 
   if (includes_nul(name, namelen))
     return UV_EINVAL;
@@ -344,8 +349,15 @@ static int uv__pipe_getsockpeername(const uv_pipe_t* handle,
                                     uv__peersockfunc func,
                                     char* buffer,
                                     size_t* size) {
+#if defined(__linux__)
+  static const int is_linux = 1;
+#else
+  static const int is_linux = 0;
+#endif
   struct sockaddr_un sa;
   socklen_t addrlen;
+  size_t slop;
+  char* p;
   int err;
 
   addrlen = sizeof(sa);
@@ -359,17 +371,20 @@ static int uv__pipe_getsockpeername(const uv_pipe_t* handle,
     return err;
   }
 
-#if defined(__linux__)
-  if (sa.sun_path[0] == 0)
-    /* Linux abstract namespace */
+  slop = 1;
+  if (is_linux && sa.sun_path[0] == '\0') {
+    /* Linux abstract namespace. Not zero-terminated. */
+    slop = 0;
     addrlen -= offsetof(struct sockaddr_un, sun_path);
-  else
-#endif
-    addrlen = strlen(sa.sun_path);
-
+  } else {
+    p = memchr(sa.sun_path, '\0', sizeof(sa.sun_path));
+    if (p == NULL)
+      p = ARRAY_END(sa.sun_path);
+    addrlen = p - sa.sun_path;
+  }
 
-  if ((size_t)addrlen >= *size) {
-    *size = addrlen + 1;
+  if ((size_t)addrlen + slop > *size) {
+    *size = addrlen + slop;
     return UV_ENOBUFS;
   }
 

test/test-list.h

@@ -209,6 +209,7 @@ TEST_DECLARE   (pipe_connect_to_file)
 TEST_DECLARE   (pipe_connect_on_prepare)
 TEST_DECLARE   (pipe_getsockname)
 TEST_DECLARE   (pipe_getsockname_abstract)
+TEST_DECLARE   (pipe_getsockname_autobind)
 TEST_DECLARE   (pipe_getsockname_blocking)
 TEST_DECLARE   (pipe_pending_instances)
 TEST_DECLARE   (pipe_sendmsg)
@@ -827,6 +828,7 @@ TASK_LIST_START
   TEST_ENTRY  (pipe_overlong_path)
   TEST_ENTRY  (pipe_getsockname)
   TEST_ENTRY  (pipe_getsockname_abstract)
+  TEST_ENTRY  (pipe_getsockname_autobind)
   TEST_ENTRY  (pipe_getsockname_blocking)
   TEST_ENTRY  (pipe_pending_instances)
   TEST_ENTRY  (pipe_sendmsg)

test/test-pipe-bind-error.c

@@ -202,7 +202,6 @@ TEST_IMPL(pipe_overlong_path) {
   ASSERT_OK(uv_run(uv_default_loop(), UV_RUN_DEFAULT));
 #endif /*if defined(_AIX) && !defined(__PASE__)*/
 #endif /* ifndef _WIN32 */
-  ASSERT_EQ(UV_EINVAL, uv_pipe_bind(&pipe, ""));
   uv_pipe_connect(&req,
                   &pipe,
                   "",
@@ -213,5 +212,4 @@ TEST_IMPL(pipe_overlong_path) {
 
   MAKE_VALGRIND_HAPPY(uv_default_loop());
   return 0;
-
 }

test/test-pipe-getsockname.c

@@ -78,6 +78,36 @@ static void pipe_client_connect_cb(uv_connect_t* req, int status) {
 }
 
 
+#if defined(__linux__)
+/* Socket name looks like \0[0-9a-f]{5}, e.g. "\0bad42" */
+static void check_is_autobind_abstract_socket_name(const char *p, size_t len) {
+  ASSERT_EQ(len, 6);
+  ASSERT_EQ(*p, '\0');
+
+  while (*p != '\0') {
+    ASSERT((*p >= '0' && *p <= '9') || (*p >= 'a' && *p <= 'f'));
+    p++;
+  }
+}
+
+
+static void pipe_client_autobind_connect_cb(uv_connect_t* req, int status) {
+  char buf[16];
+  size_t len;
+
+  ASSERT_OK(status);
+  len = 5;
+  ASSERT_EQ(UV_ENOBUFS, uv_pipe_getpeername(&pipe_client, buf, &len));
+  len = 6;
+  ASSERT_OK(uv_pipe_getpeername(&pipe_client, buf, &len));
+  check_is_autobind_abstract_socket_name(buf, len);
+  pipe_client_connect_cb_called++;
+  uv_close((uv_handle_t*) &pipe_client, pipe_close_cb);
+  uv_close((uv_handle_t*) &pipe_server, pipe_close_cb);
+}
+#endif  /* defined(__linux__) */
+
+
 static void pipe_server_connection_cb(uv_stream_t* handle, int status) {
   /* This function *may* be called, depending on whether accept or the
    * connection callback is called first.
@@ -124,9 +154,11 @@ TEST_IMPL(pipe_getsockname) {
   ASSERT_STR_EQ(pipe_server.pipe_fname, TEST_PIPENAME);
 #endif
 
-  len = sizeof buf;
-  r = uv_pipe_getsockname(&pipe_server, buf, &len);
-  ASSERT_OK(r);
+  len = sizeof(TEST_PIPENAME) - 1;
+  ASSERT_EQ(UV_ENOBUFS, uv_pipe_getsockname(&pipe_server, buf, &len));
+
+  len = sizeof(TEST_PIPENAME);
+  ASSERT_OK(uv_pipe_getsockname(&pipe_server, buf, &len));
 
   ASSERT_NE(0, buf[len - 1]);
   ASSERT_EQ(buf[len], '\0');
@@ -160,7 +192,8 @@ TEST_IMPL(pipe_getsockname) {
 
   len = sizeof buf;
   r = uv_pipe_getsockname(&pipe_client, buf, &len);
-  ASSERT(r == 0 && len == 0);
+  ASSERT_EQ(r, 0);
+  ASSERT_EQ(len, 0);
 
   len = sizeof buf;
   r = uv_pipe_getpeername(&pipe_client, buf, &len);
@@ -228,6 +261,44 @@ TEST_IMPL(pipe_getsockname_abstract) {
 #endif
 }
 
+
+TEST_IMPL(pipe_getsockname_autobind) {
+#if defined(__linux__)
+  char buf[256];
+  size_t buflen;
+
+  buflen = sizeof(buf);
+  memset(buf, 0, sizeof(buf));
+  ASSERT_OK(uv_pipe_init(uv_default_loop(), &pipe_server, 0));
+  ASSERT_OK(uv_pipe_bind2(&pipe_server, "", 0, 0));
+  ASSERT_OK(uv_pipe_getsockname(&pipe_server, buf, &buflen));
+  check_is_autobind_abstract_socket_name(buf, buflen);
+  ASSERT_OK(uv_listen((uv_stream_t*) &pipe_server, 0,
+                      pipe_server_connection_cb));
+  ASSERT_OK(uv_pipe_init(uv_default_loop(), &pipe_client, 0));
+  ASSERT_OK(uv_pipe_connect2(&connect_req, &pipe_client,
+                             buf,
+                             1 + strlen(&buf[1]),
+                             0,
+                             pipe_client_autobind_connect_cb));
+  ASSERT_OK(uv_run(uv_default_loop(), UV_RUN_DEFAULT));
+  ASSERT_EQ(1, pipe_client_connect_cb_called);
+  ASSERT_EQ(2, pipe_close_cb_called);
+  MAKE_VALGRIND_HAPPY(uv_default_loop());
+  return 0;
+#else
+  /* On other platforms it should simply fail with UV_EINVAL. */
+  ASSERT_OK(uv_pipe_init(uv_default_loop(), &pipe_server, 0));
+  ASSERT_EQ(UV_EINVAL, uv_pipe_bind2(&pipe_server, "", 0, 0));
+  uv_close((uv_handle_t*) &pipe_server, pipe_close_cb);
+  ASSERT_OK(uv_run(uv_default_loop(), UV_RUN_DEFAULT));
+  ASSERT_EQ(1, pipe_close_cb_called);
+  MAKE_VALGRIND_HAPPY(uv_default_loop());
+  return 0;
+#endif
+}
+
+
 TEST_IMPL(pipe_getsockname_blocking) {
 #ifdef _WIN32
   HANDLE readh, writeh;