Re: sh(1) exec redirection

[Robert Elz <kre%munnari.OZ.AU@localhost>]

    Date:        Tue, 5 Nov 2024 17:55:38 +0100
    From:        Edgar =?iso-8859-1?B?RnXf?= <ef%math.uni-bonn.de@localhost>
    Message-ID:  <ZypOCnQfvxWmt4bq%trav.math.uni-bonn.de@localhost>

  | 1.40 tried to fix it, but probably 
  | not for the command being exec'ed being exec.

Yes, that is exactly the issue, we want

	exec 3>whatever

to set close-on-exec (by default) as typically fds
created that way are just for the script to use, and
shouldn't be passed through to children.

(This was needed as otherwise private fd's required for
/etc/rc to work properly were being passed through to all
the commands (daemons in particular) started by rc ... Now
we'd probably just use fdflags to set close-on-exec on those
fds rather than do it this way, but I don't think that existed
yet when this was changed).

So "exec" was given an exemption to the "no redirects on the command
line have close-on-exec" rule (a redirect explicitly for a command
clearly should be passed to that command).  All the shell's private
fd's (such as the one used to read a script file) get close-on-exec.

But the case of

	exec cmd 3>whatever

also got the exemption (because it is "exec"), even though that is
really just sort of

	cmd 3>whatever
	exit

(without the fork that would be needed to run cmd that way)

The fix for this is a little bit ugly, but seems to work OK.

Coming soon (but not to -8!   Perhaps not -9 either, I'll need
to check that one, -10 should be possible).

kre