linux-kernel - Re: CVE-2024-26774: ext4: avoid dividing by 0 in mb_update_avg_fragment

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Message-ID: <20240417152941.GD2277619@mit.edu>
Date: Wed, 17 Apr 2024 11:29:41 -0400
From: "Theodore Ts'o" <tytso@....edu>
To: Jan Kara <jack@...e.cz>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, cve@...nel.org,
        linux-kernel@...r.kernel.org, linux-cve-announce@...r.kernel.org
Subject: Re: CVE-2024-26774: ext4: avoid dividing by 0 in
 mb_update_avg_fragment_size() when block bitmap corrupt

On Wed, Apr 17, 2024 at 04:54:46PM +0200, Jan Kara wrote:
> So if we should honestly state the situation (and filesystem folks are
> trying to get this message across for a few years already), we should issue
> a CVE for "mounting untrusted fs image can crash your kernel or install
> rootkit to your system". And yes, I know most distros will happily mount
> whatever is plugged into the USB port because that is what users expect and
> it is convenient. So if anybody wants a practical solution to this security
> problem, I'd suggest working on FUSE drivers for filesystems you care about
> and make distros use that when mounting removable media... That is actually
> pretty secure and robust solution if you don't care about performance
> *that* much.

I will note that the insistence of enabling the automounter is
apparently the fault of some Red Hat product manager.  Alas, our
requests to "cut that out" have been ignored.

I'll also note that Darrick and I have included udev rules in xfsprogs
and e2fsprogs to disable the automounter for ext4 and xfs file
systems.  I believe the xfsprogs udev rules have already been
released, and the ext4 udev rules in e2fsprogs will be released in the
next upstream release.

It will be interesting to see how many distributions explicitly decide
to override our udev rules....  If they do, hopefully the security
liability will attach to those distributions, and they will get
everything that they deserve.

Humming "Flexing like a godd*mn acrobat ; Karma and I vibe like that",

						- Ted