archive mirror
 help / color / mirror / Atom feed
From: Filipe Manana <>
To: Rob Landley <>
Cc:, enh <>
Subject: Re: Endless readdir() loop on btrfs.
Date: Sun, 13 Aug 2023 12:37:00 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Sun, Aug 13, 2023 at 12:04 AM Rob Landley <> wrote:
> Would anyone like to comment on:
> which resulted from:
> and just got re-reported as:
> 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:

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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).