linux-kernel - Re: [PATCH v6 0/3] implement OA2_CRED

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Message-ID: <125b6804-d9f8-4c36-83cd-36143ba1045d@yandex.ru>
Date: Tue, 21 May 2024 23:35:16 +0300
From: stsp <stsp2@...dex.ru>
To: Jann Horn <jannh@...gle.com>
Cc: linux-kernel@...r.kernel.org, Stefan Metzmacher <metze@...ba.org>,
 Eric Biederman <ebiederm@...ssion.com>,
 Alexander Viro <viro@...iv.linux.org.uk>, Andy Lutomirski <luto@...nel.org>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 Jeff Layton <jlayton@...nel.org>, Chuck Lever <chuck.lever@...cle.com>,
 Alexander Aring <alex.aring@...il.com>,
 David Laight <David.Laight@...lab.com>, linux-fsdevel@...r.kernel.org,
 linux-api@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
 Christian Göttsche <cgzones@...glemail.com>
Subject: Re: [PATCH v6 0/3] implement OA2_CRED_INHERIT flag for openat2()

21.05.2024 22:01, Jann Horn пишет:
> On Sat, Apr 27, 2024 at 1:24 PM Stas Sergeev <stsp2@...dex.ru> wrote:
>> This patch-set implements the OA2_CRED_INHERIT flag for openat2() syscall.
>> It is needed to perform an open operation with the creds that were in
>> effect when the dir_fd was opened, if the dir was opened with O_CRED_ALLOW
>> flag. This allows the process to pre-open some dirs and switch eUID
>> (and other UIDs/GIDs) to the less-privileged user, while still retaining
>> the possibility to open/create files within the pre-opened directory set.
> As Andy Lutomirski mentioned before, Linux already has Landlock
> (https://docs.kernel.org/userspace-api/landlock.html) for unprivileged
> filesystem sandboxing. What benefits does OA2_CRED_INHERIT have
> compared to Landlock?

The idea is different.
OA2_CRED_INHERIT was supposed to give you an additional access (to what 
you can't access otherwise, after a priv drop), while landlock allows 
you to explicitly restrict an access. OA2_CRED_INHERIT more answered 
with idmapped mounts rather than the landlock, but idmapped mounts are 
not fully unpriv'd.