linux-kernel - Re: [PATCH bpf-next 2/2] selftests/bpf: Extend test fs

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Message-ID: <ZyMqOyswxw1s1Jbt@infradead.org>
Date: Wed, 30 Oct 2024 23:56:59 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Song Liu <songliubraving@...a.com>
Cc: Christoph Hellwig <hch@...radead.org>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	Song Liu <song@...nel.org>, bpf <bpf@...r.kernel.org>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Kernel Team <kernel-team@...a.com>,
	Andrii Nakryiko <andrii@...nel.org>,
	Eduard Zingerman <eddyz87@...il.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Al Viro <viro@...iv.linux.org.uk>, KP Singh <kpsingh@...nel.org>,
	Matt Bobrowski <mattbobrowski@...gle.com>
Subject: Re: [PATCH bpf-next 2/2] selftests/bpf: Extend test fs_kfuncs to
 cover security.bpf xattr names

On Wed, Oct 30, 2024 at 08:44:26PM +0000, Song Liu wrote:
> Given bpf kfuncs can read user.* xattrs for almost a year now, I think we 
> cannot simply revert it. We already have some users using it. 
> 
> Instead, we can work on a plan to deprecated it. How about we add a 
> WARN_ON_ONCE as part of this patchset, and then remove user.* support 
> after some time?

As Christian mentioned having bpf access to user xattrs is probably
not a big issue.  OTOH anything that makes security decisions based
on it is probably pretty broken.  Not sure how you want to best
handle that.