From: Rob Landley <rob@landley.net>
To: linux-btrfs@vger.kernel.org
Cc: enh <enh@google.com>
Subject: Endless readdir() loop on btrfs.
Date: Sat, 12 Aug 2023 16:52:06 -0500 [thread overview]
Message-ID: <2c8c55ec-04c6-e0dc-9c5c-8c7924778c35@landley.net> (raw)
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...
Rob
next reply other threads:[~2023-08-12 21:50 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-12 21:52 Rob Landley [this message]
2023-08-13 11:37 ` Endless readdir() loop on btrfs Filipe Manana
2023-08-13 16:43 ` Rob Landley
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