[patch] SOCK_CLOEXEC, SOCK_NONBLOCK and MSG_CMSG_CLOEXEC

[Konstantin Belousov]

On Sun, Mar 17, 2013 at 10:23:53PM +0100, Jilles Tjoelker wrote:
> Here are some more modifications to allow creating file descriptors with
> close-on-exec set. Like in linux/glibc, SOCK_CLOEXEC and SOCK_NONBLOCK
> can be OR'ed in socket() and socketpair()'s type parameter, and
> MSG_CMSG_CLOEXEC to recvmsg() makes file descriptors (SCM_RIGHTS)
> atomically close-on-exec.
> 
> The numerical values for SOCK_CLOEXEC and SOCK_NONBLOCK are as in
> NetBSD. MSG_CMSG_CLOEXEC is the first free bit for MSG_*.
> 
> I do not pass the SOCK_* flags to MAC because this may cause incorrect
> failures and can be done later via fcntl() anyway. I expect audit to
> cope with the new flags.
> 
> For MSG_CMSG_CLOEXEC, I had to change unp_externalize to take a flags
> argument.

This looks fine to me.

The only note I have, which is not directly related to your patch,
is the recvmsg(2) behaviour when the undefined flag is passed.
The syscall silently ignores the flags. I think this is quite wrong,
and would cause interesting (security) implications if the program
using the MSG_CMSG_CLOEXEC is run on older kernel which does not
interpret the flag.

Might be, we should start returning EINVAL for unknown flag, despite
SUSv4 not specifying the condition ?
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