linux-kernel - Re: [PATCH bpf-next 3/4] bpf: Introduce path iterator

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Message-ID: <CAPhsuW78L8WUkKz8iJ1whrZ2gLJR+7Kh59eFrSXvrxP0DwMGig@mail.gmail.com>
Date: Thu, 29 May 2025 10:05:59 -0700
From: Song Liu <song@...nel.org>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Jan Kara <jack@...e.cz>, Al Viro <viro@...iv.linux.org.uk>, bpf <bpf@...r.kernel.org>, 
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	LSM List <linux-security-module@...r.kernel.org>, Kernel Team <kernel-team@...a.com>, 
	Andrii Nakryiko <andrii@...nel.org>, Eduard <eddyz87@...il.com>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Christian Brauner <brauner@...nel.org>, KP Singh <kpsingh@...nel.org>, 
	Matt Bobrowski <mattbobrowski@...gle.com>, Amir Goldstein <amir73il@...il.com>, repnop@...gle.com, 
	Jeff Layton <jlayton@...nel.org>, Josef Bacik <josef@...icpanda.com>, 
	Mickaël Salaün <mic@...ikod.net>, 
	Günther Noack <gnoack@...gle.com>
Subject: Re: [PATCH bpf-next 3/4] bpf: Introduce path iterator

On Thu, May 29, 2025 at 9:57 AM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
[...]
> >
> > How about we describe this as:
> >
> > Introduce a path iterator, which safely (no crash) walks a struct path.
> > Without malicious parallel modifications, the walk is guaranteed to
> > terminate. The sequence of dentries maybe surprising in presence
> > of parallel directory or mount tree modifications and the iteration may
> > not ever finish in face of parallel malicious directory tree manipulations.
>
> Hold on. If it's really the case then is the landlock susceptible
> to this type of attack already ?
> landlock may infinitely loop in the kernel ?

I think this only happens if the attacker can modify the mount or
directory tree as fast as the walk, which is probably impossible
in reality.

Thanks,
Song