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

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Message-ID: <Zw384bed3yVgZpoc@infradead.org>
Date: Mon, 14 Oct 2024 22:25:53 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Song Liu <songliubraving@...a.com>
Cc: Christoph Hellwig <hch@...radead.org>, 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>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	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 Tue, Oct 15, 2024 at 05:21:48AM +0000, Song Liu wrote:
> >> Extend test_progs fs_kfuncs to cover different xattr names. Specifically:
> >> xattr name "user.kfuncs", "security.bpf", and "security.bpf.xxx" can be
> >> read from BPF program with kfuncs bpf_get_[file|dentry]_xattr(); while
> >> "security.bpfxxx" and "security.selinux" cannot be read.
> > 
> > So you read code from untrusted user.* xattrs?  How can you carve out
> > that space and not known any pre-existing userspace cod uses kfuncs
> > for it's own purpose?
> 
> I don't quite follow the comment here. 
> 
> Do you mean user.* xattrs are untrusted (any user can set it), so we 
> should not allow BPF programs to read them? Or do you mean xattr 
> name "user.kfuncs" might be taken by some use space?

All of the above.