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Date:   Tue, 9 Nov 2021 16:26:46 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Jan Kara <jack@suse.cz>
Cc:     linux-fsdevel@vger.kernel.org,
        Nathan Wilson <nate@chickenbrittle.com>, stable@vger.kernel.org
Subject: Re: [PATCH] udf: Fix crash after seekdir
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On Tue, Nov 09, 2021 at 12:48:41PM +0100, Jan Kara wrote:
> udf_readdir() didn't validate the directory position it should start
> reading from. Thus when user uses lseek(2) on directory file descriptor
> it can trick udf_readdir() into reading from a position in the middle of
> directory entry which then upsets directory parsing code resulting in
> errors or even possible kernel crashes. Similarly when the directory is
> modified between two readdir calls, the directory position need not be
> valid anymore.

... We don't have an xfstest for this already?  Actually, two.  One for
lseek() and one for modifying the directory as it's being read.