rb_wait_for_single_fd: do not OOM or segfault with invalid FD on select()

Instead, match the poll() implementation used on Linux for now;
as the Linux poll(2) manpage describes using negative FD to
easily ignore an FD in a larger FD set while (sleeping the given
timeout).  I'm not entirely sure if matching poll() behavior
is a good idea for a single FD, but it's better than segfaulting
or NoMemoryError.

* thread.c (init_set_fd): ignore negative FD
* test/-ext-/wait_for_single_fd/test_wait_for_single_fd.rb
  (test_wait_for_invalid_fd): check values which may trigger
  segfaults or OOM

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58925 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 3 insertions, 0 deletions

diff --git a/thread.c b/thread.c
index 76fb1360c9..4d954c76de 100644
--- a/thread.c
+++ b/thread.c
@@ -3969,6 +3969,9 @@ rb_wait_for_single_fd(int fd, int events, struct timeval *tv)
 static rb_fdset_t *
 init_set_fd(int fd, rb_fdset_t *fds)
 {
+    if (fd < 0) {
+	return 0;
+    }
     rb_fd_init(fds);
     rb_fd_set(fd, fds);