unix: set close-on-exec flag on received file descriptors

[bnoordhuis]

Set the close-on-exec flag on file descriptors that are received with recvmsg().

For reference: https://groups.google.com/forum/#!topic/nodejs/8HbK7MAGAGg (Message-ID <CAPJ5V2bmXQHKzXbu2fN_4zBinjyrbGQ_s7QPEpazDush4SuZbQ@mail.gmail.com>)

Example patch:

diff --git a/deps/uv/src/unix/stream.c b/deps/uv/src/unix/stream.c
index c9df979..dff5f2b 100644
--- a/src/unix/stream.c
+++ b/src/unix/stream.c
@@ -1042,6 +1042,7 @@ static void uv__read(uv_stream_t* stream) {
               void* pv = CMSG_DATA(cmsg);
               int* pi = pv;
               stream->accepted_fd = *pi;
+              uv__cloexec(stream->accepted_fd, 1);
             }

           } else {

[saghul]

This kind of fell through the cracks :-S Looks kind-of important, think we should adapt and land @indutny? Ben?

[bnoordhuis]

Seems like a good idea, yes. I fixed it in master in e9f75fb, introducing a style error in internal.h in the process, it seems.

I would suggest the same approach for v0.10: use recvmsg(MSG_CMSG_CLOEXEC) when available, fall back to uv__cloexec() when it's not.

[saghul]

Will do, thanks for confirming Ben!