From: "Alex Xu (Hello71)" <alex_y_xu@yahoo.ca>
To: musl@lists.openwall.com, Markus Wichmann <nullplan@gmx.net>
Subject: Re: [musl] Feasibility of FD_CLOEXEC on all streams
Date: Sun, 19 Dec 2021 09:54:32 -0500 [thread overview]
Message-ID: <1639925208.rmnuvpezrd.none@localhost> (raw)
In-Reply-To: <20211218172646.GP7074@brightrain.aerifal.cx>
Excerpts from Rich Felker's message of December 18, 2021 12:26 pm:
> On Sat, Dec 18, 2021 at 12:14:15PM -0500, Rich Felker wrote:
>> On Sat, Dec 18, 2021 at 05:33:20PM +0100, Markus Wichmann wrote:
>> > Hi all,
>> >
>> > I was recently reading the source code of popen(), and noticed that it
>> > has to iterate over all open files to close all the open pipe FDs the
>> > child might inherit. And that made me wonder:
>> >
>> > 1. Does POSIX allow for all FILE streams to have FD_CLOEXEC applied by
>> > default?
>>
>> No. Accessing fileno(f) is permissible subject to following the rules
>> for active handle:
>>
>> https://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_05_01
>>
>> and that entails being able to use them according to the rules for how
>> fds are inherited across exec.
>
> Also, the POSIX spec for fopen is rather explicit:
>
> "[CX] The file descriptor associated with the opened stream shall
> be allocated and opened as if by a call to open() with the
> following flags: ..."
>
> https://pubs.opengroup.org/onlinepubs/9699919799/functions/fopen.html
>
> Rich
>
Playing devil's advocate here, can't the implementation unset FD_CLOEXEC
when fileno is called? This doesn't fix the latter issue, but if that's
the only problem then I would argue that it can be sufficiently covered
by the as-if rule. It also wouldn't fix the popen loop, but would still
add some hardening for poorly written programs.
Cheers,
Alex.
next prev parent reply other threads:[~2021-12-19 14:54 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-18 16:33 Markus Wichmann
2021-12-18 17:14 ` Rich Felker
2021-12-18 17:26 ` Rich Felker
2021-12-19 14:54 ` Alex Xu (Hello71) [this message]
2021-12-19 15:22 ` Rich Felker
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