pidfd: Add missing sock updates for pidfd_getfd()

The sock counting (sock_update_netprioidx() and sock_update_classid())
was missing from pidfd's implementation of received fd installation. Add
a call to the new __receive_sock() helper.

Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Sargun Dhillon <sargun@sargun.me>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
Fixes: 8649c32 ("pid: Implement pidfd_getfd syscall")
Signed-off-by: Kees Cook <keescook@chromium.org>

kernel/pid.c

@@ -42,6 +42,7 @@
 #include <linux/sched/signal.h>
 #include <linux/sched/task.h>
 #include <linux/idr.h>
+#include <net/sock.h>
 
 struct pid init_struct_pid = {
 	.count		= REFCOUNT_INIT(1),
@@ -642,10 +643,12 @@ static int pidfd_getfd(struct pid *pid, int fd)
 	}
 
 	ret = get_unused_fd_flags(O_CLOEXEC);
-	if (ret < 0)
+	if (ret < 0) {
 		fput(file);
-	else
+	} else {
+		__receive_sock(file);
 		fd_install(ret, file);
+	}
 
 	return ret;
 }