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

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Date:	Fri, 9 Jan 2015 11:13:03 -0500
From:	Rich Felker <dalias@...ifal.cx>
To:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:	David Drysdale <drysdale@...gle.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andy Lutomirski <luto@...capital.net>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Meredydd Luff <meredydd@...atehouse.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>,
	Arnd Bergmann <arnd@...db.de>,
	Christoph Hellwig <hch@...radead.org>, x86@...nel.org,
	linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
	sparclinux@...r.kernel.org
Subject: Re: [PATCHv10 man-pages 5/5] execveat.2: initial man page for
 execveat(2)

On Fri, Jan 09, 2015 at 04:47:31PM +0100, Michael Kerrisk (man-pages) wrote:
> On 11/24/2014 12:53 PM, David Drysdale wrote:
> > Signed-off-by: David Drysdale <drysdale@...gle.com>
> > ---
> >  man2/execveat.2 | 153 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 153 insertions(+)
> >  create mode 100644 man2/execveat.2
> 
> David,
> 
> Thanks for the very nicely prepared man page. I've done 
> a few very light edits, and will release the version below 
> with the next man-pages release.
> 
> I have one question. In the message accompanying
> commit 51f39a1f0cea1cacf8c787f652f26dfee9611874 you wrote:
> 
>   The filename fed to the executed program as argv[0] (or the name of the
>   script fed to a script interpreter) will be of the form "/dev/fd/<fd>"
>   (for an empty filename) or "/dev/fd/<fd>/<filename>", effectively
>   reflecting how the executable was found.  This does however mean that
>   execution of a script in a /proc-less environment won't work; also, script
>   execution via an O_CLOEXEC file descriptor fails (as the file will not be
>   accessible after exec).
> 
> How does one produce this situation where the execed program sees 
> argv[0] as a /dev/fd path? (i.e., what would the execveat()
> call look like?) I tried to produce this scenario, but could not.

I think this is wrong. argv[0] is an arbitrary string provided by the
caller and would never be derived from the fd passed. 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.

Rich
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