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

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Message-ID: <CAO8a2SiN+cnsK5LGMV+6jZM=VcO5kmxkTH1mR1bLF6Z5cPxH9A@mail.gmail.com>
Date: Mon, 25 Nov 2024 15:23:57 +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

Hey, Folks.
This seems important, so I'm bumping this thread. Max has a valid
concern, and this issue must be addressed.
Jeff seems to think keeping at least a few retries might be a good idea.

Max, could you add a cap on the retry count to your original patch? I
will discuss the PATH_MAX with Patrick and open a feature request for
myself to alleviate the limitation.

On Thu, Nov 21, 2024 at 12:48 PM Alex Markuze <amarkuze@...hat.com> wrote:
>
> 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
> >
> >