Re: [PATCHv10 man-pages 5/5] execveat.2: initial man page for execveat(2)

[Rich Felker]

On Fri, Jan 09, 2015 at 05:46:28PM +0000, David Drysdale wrote:
> > It's AT_EXECFN,
> > /proc/self/exe, and filenames shown elsewhere in /proc that may be
> > derived in odd ways.
> >
> > I would also move the text about O_CLOEXEC to a BUGS or NOTES section
> > rather than the main description. The long-term intent should be that
> > script execution this way should work. IIRC this was discussed earlier
> > in the thread.
> 
> I may be misremembering, but I thought we hoped to be able to fix
> execveat of a script without /proc in future, but didn't expect to fix
> execveat of a script via an O_CLOEXEC fd (because in the latter
> case the fd gets closed before the script interpreter runs, so even
> if the interpreter (or a special filesystem) does clever things for names
> starting with "/dev/fd/..." the file descriptor is already gone).

I think this is a case that needs to be fixed, though it's hard. The
normal correct usage for fexecve is to always pass an O_CLOEXEC file
descriptor, and the caller can't really be expected to know whether
the file is a script or not. We discussed workarounds before and one
idea I proposed was having fexecve provide a "one open only" magic
symlink in /proc/self/ to pass to the interpreter. It would behave
like an O_PATH file descriptor magic symlink in /proc/self/fd, but
would automatically cease to exist on the first open (at which point
the interpreter would have a real O_RDONLY file descriptor for the
underlying file).

Rich
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