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Date: Fri, 9 Jan 2015 21:09:41 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Rich Felker <dalias@aerifal.cx>
Cc: David Drysdale <drysdale@google.com>,
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Subject: Re: [PATCHv10 man-pages 5/5] execveat.2: initial man page for
 execveat(2)
Message-ID: <20150109210941.GL22149@ZenIV.linux.org.uk>
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On Fri, Jan 09, 2015 at 03:59:26PM -0500, Rich Felker wrote:

> > For fsck sake, folks, if you have bloody /proc, you don't need that shite
> > at all!  Just do execve on /proc/self/fd/n, and be done with that.
> > 
> > The sole excuse for merging that thing in the first place had been
> > "would anybody think of children^Wsclerotic^Whardened environments
> > where they have no /proc at all".
> 
> That doesn't work. With O_CLOEXEC, /proc/self/fd/n is already gone at
> the time the interpreter runs, whether you're using fexecveat or
> execve with "/proc/self/fd/n" to implement POSIX fexecve(). That's the
> problem. This breaks the intended idiom for fexecve.

Just what will your magical symlink do in case when the file is opened,
unlinked and marked O_CLOEXEC?  When should actual freeing of disk blocks,
etc. happen?  And no, you can't assume that interpreter will open the
damn thing even once - there's nothing to oblige it to do so.

Al, more and more tempted to ask reverting the whole thing - this hardcoded
/dev/fd/... (in fs/exec.c, no less) is disgraceful enough, but threats of
even more revolting kludges in the name of "intended idiom for fexecve"...