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From: Filipe Manana <fdmanana@kernel.org>
To: Rob Landley <rob@landley.net>
Cc: linux-btrfs@vger.kernel.org, enh <enh@google.com>
Subject: Re: Endless readdir() loop on btrfs.
Date: Sun, 13 Aug 2023 12:37:00 +0100	[thread overview]
Message-ID: <CAL3q7H6ehkiLBZpfFf3dy7whnE1fWK5HhW6XdNbYAu2FtqNHxA@mail.gmail.com> (raw)
In-Reply-To: <2c8c55ec-04c6-e0dc-9c5c-8c7924778c35@landley.net>

On Sun, Aug 13, 2023 at 12:04 AM Rob Landley <rob@landley.net> wrote:
>
> Would anyone like to comment on:
>
>   https://bugzilla.kernel.org/show_bug.cgi?id=217681
>
> which resulted from:
>
>   https://github.com/landley/toybox/issues/306
>
> and just got re-reported as:
>
>   https://github.com/landley/toybox/issues/448
>
> The issue is that modifications to the directory during a getdents()
> deterministically append the modified entry to the getdents(), which means
> directory traversal is never guaranteed to end, which seems like a denial of
> service attack waiting to happen.
>
> This is not a problem on ext4 or tmpfs or vfat or the various flash filesystems,
> where readdir() reliably completes. This is a btrfs-specific problem.
>
> I can try to add a CONFIG_BTRFS_BUG optional workaround comparing the dev:inode
> pair of returned entries to filter out ones I've already seen, but can I
> reliably stop at the first duplicate or do I have to continue to see if there's
> more I haven't seen yet? (I dunno what your return order is.) If some OTHER
> process is doing a "while true; do mv a b; mv b a; done" loop in a directory,
> that could presumably pin any OTHER process doing a naieve readdir() loop over
> that directory, hence denial of service...

I've just sent a fix for this, it's at:

https://lore.kernel.org/linux-btrfs/c9ceb0e15d92d0634600603b38965d9b6d986b6d.1691923900.git.fdmanana@suse.com/

Thanks for the report.

>
> Rob

  reply	other threads:[~2023-08-13 11:37 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-08-12 21:52 Endless readdir() loop on btrfs Rob Landley
2023-08-13 11:37 ` Filipe Manana [this message]
2023-08-13 16:43   ` Rob Landley

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