linux-kernel - Re: [PATCH 0/2] fs: fix capable() call in simple_xattr

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Message-ID: <20220905090811.ocnnc53y2bow7m3i@wittgenstein>
Date:   Mon, 5 Sep 2022 11:08:11 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Ondrej Mosnacek <omosnace@...hat.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        Martin Pitt <mpitt@...hat.com>, Vasily Averin <vvs@...nvz.org>
Subject: Re: [PATCH 0/2] fs: fix capable() call in simple_xattr_list()

On Thu, Sep 01, 2022 at 05:26:30PM +0200, Ondrej Mosnacek wrote:
> The goal of these patches is to avoid calling capable() unconditionally
> in simple_xattr_list(), which causes issues under SELinux (see
> explanation in the second patch).
> 
> The first patch tries to make this change safer by converting
> simple_xattrs to use the RCU mechanism, so that capable() is not called
> while the xattrs->lock is held. I didn't find evidence that this is an
> issue in the current code, but it can't hurt to make that change
> either way (and it was quite straightforward).

Hey Ondrey,

There's another patchset I'd like to see first which switches from a
linked list to an rbtree to get rid of performance issues in this code
that can be used to dos tmpfs in containers:

https://lore.kernel.org/lkml/d73bd478-e373-f759-2acb-2777f6bba06f@openvz.org

I don't think Vasily has time to continue with this so I'll just pick it
up hopefully this or the week after LPC.

Christian