linux-kernel - Re: TOCTOU-free exec(), chdir(), open() with O

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Message-ID: <RpoPywKbvpClHVGTO6u6Bprtwk6A0wfF2xafV4MBEWVBFZ1xErnFrJjlVFVRx7Bo4qrWHJcOj3_-AH5LWDaOwj6Zn4Dn7w5wSgKX8BmN3cw=@chesswob.org>
Date: Mon, 26 Aug 2024 17:07:18 +0000
From: Ⓐlï P☮latel <alip@...sswob.org>
To: Bagas Sanjaya <bagasdotme@...il.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Linux Security Module Subsystem <linux-security-module@...r.kernel.org>, Kees Cook <keescook@...omium.org>, Andy Lutomirski <luto@...capital.net>, Will Drewry <wad@...omium.org>, Mickaël Salaün <mic@...ikod.net>, Theodore Ts'o <tytso@....edu>, Alan Stern <stern@...land.harvard.edu>
Subject: Re: TOCTOU-free exec(), chdir(), open() with O_PATH sandbox emulation support?

On Thursday, February 22nd, 2024 at 07:41, Bagas Sanjaya <bagasdotme@...il.com> wrote:

> Hi,
> 

> Ali Polatel alip@...sswob.org opened feature request bug on Bugzilla
> 

> regarding TOCTOU-free sandbox emulation support [1]. He wrote:
[snip]
> Is the feature request viable/realistic?
> 

> Thanks.
> 

> [1]: https://bugzilla.kernel.org/show_bug.cgi?id=218501

Just close it as ENOTG**GLE. Sorry for the noise¹...

All of these have "safe" workarounds:
1. PTRACE_EVENT_EXEC can workaround the inability to emulate exec.
   That said, you can TOCTOU scripts (because binfmt) but not ELFs!
   Just denylist the interpreters or W^X your FS like a chad or wait
   for O_MAYEXEC to happen if you care that much really.
2. Turn O_PATH to O_RDONLY and noone will know (pinky swear). You get to
   updoot access times but who cares if the alternative is unsafe?
3. Apparently, chdir is not seen as security critical² so why bother?

> --
> An old man doll... just what I always wanted! - Clara

¹: you cannot cover the sun with a sieve,
gv*sor is a joke: https://mastodon.online/@alip/113028762062293426
²: https://www.openwall.com/lists/oss-security/2024/05/20/1

--  
-Ⓐlïp.
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