linux-kernel - Re: [PATCH] fs/ceph/mds_client: give up on paths longer than PATH

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Message-ID: <CAO8a2SiRwVUDT8e3fN1jfFOw3Z92dtWafZd8M6MHB57D3d_wvg@mail.gmail.com>
Date: Thu, 21 Nov 2024 12:48:07 +0200
From: Alex Markuze <amarkuze@...hat.com>
To: Patrick Donnelly <pdonnell@...hat.com>
Cc: Max Kellermann <max.kellermann@...os.com>, Jeff Layton <jlayton@...nel.org>, 
	Ilya Dryomov <idryomov@...il.com>, Venky Shankar <vshankar@...hat.com>, xiubli@...hat.com, 
	ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org, dario@...e53.de, 
	stable@...r.kernel.org
Subject: Re: [PATCH] fs/ceph/mds_client: give up on paths longer than PATH_MAX

IMHO, we should first have a solution for the immediate problem,
remove infinite retries and fail early, and cap it at 3 retries in
case there is a temporary issue here.
I would use ENAMETOOLONG as the primary error code, as it is the most
informative, and couple it with a rate-limited kernel log
(pr_warn_once) for debugging without flooding.
I would also open a bug/feature request for a dynamic buffer
allocation that bypasses PATH_MAX for protocol-specific paths.

On Tue, Nov 19, 2024 at 5:17 PM Patrick Donnelly <pdonnell@...hat.com> wrote:
>
> On Tue, Nov 19, 2024 at 9:54 AM Max Kellermann <max.kellermann@...os.com> wrote:
> >
> > On Tue, Nov 19, 2024 at 2:58 PM Patrick Donnelly <pdonnell@...hat.com> wrote:
> > > The protocol does **not** require building the full path for most
> > > operations unless it involves a snapshot.
> >
> > We don't use Ceph snapshots, but before today's emergency update, we
> > could shoot down an arbitrary server with a single (unprivileged)
> > system call using this vulnerability.
> >
> > I'm not sure what your point is, but this vulnerability exists, it
> > works without snapshots and we think it's serious.
>
> I'm not suggesting there isn't a bug. I'm correcting a misunderstanding.
>
> --
> Patrick Donnelly, Ph.D.
> He / Him / His
> Red Hat Partner Engineer
> IBM, Inc.
> GPG: 19F28A586F808C2402351B93C3301A3E258DD79D
>
>