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List:       fedora-devel-list
Subject:    Re: Restricting automounting of uncommon filesystems?
From:       "Richard W.M. Jones" <rjones () redhat ! com>
Date:       2023-07-22 10:55:50
Message-ID: 20230722105247.GC7781 () redhat ! com
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On Sat, Jul 22, 2023 at 07:01:34AM +0100, Matthew Garrett wrote:
> A discussion within Debian again brought up the problem that:
> 
> 1) Automounting of removable media exposes the kernel to a lot of 
> untrusted input 
> 2) Kernel upstream are not terribly concerned with ensuring that kernel 
> filesystems are resilient against deliberately malformed filesystems so 
> are mostly not proactively looking for bugs there
> 3) Uncommonly used filesystems are less likely to be tested against 
> adverse input in the real world and so are more likely to contain 
> exploitable bugs
> 
> There are various cases where people do need to make use of uncommon 
> filesystems, but the majority of them aren't related to removable media. 
> udisks2 supports setting the UDISKS_AUTO variable to 0 on devices that
> shouldn't be automounted, which means something like:
> 
> SUBSYSTEM!="block", GOTO="udisks_insecure_fs_end"
> ENV{ID_FS_TYPE}=="hfs", ENV{UDISKS_AUTO}="0"
> # repeat as necessary for anything else that shouldn't be automounted
> LABEL="udisks_insecure_fs_end"
> 
> ought to be enough. So:
> 
> a) Does this seem like a good idea?
> b) If so, is dealing with it via udev rules the right approach? This way 
> seems desktop-agnostic
> c) Where should it ship, and what should the process be for disabling it 
> for people who need this functionality?
> 
> Long-term I'd love to see more work put into having FUSE support for 
> these and leaving the in-kernel fs to stuff we know is trustworthy, but 
> that's rather more work.

Well, libguestfs is a thing.

Are any filesystems really trusted?

I do take your point though that some kernel-supported filesystems are
hardly ever used and you should probably need to take special steps to
expose them to your kernel.  At least Fedora no longer enables the BBC
Micro filesystem, last widely used in the 1980s.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-p2v converts physical machines to virtual machines.  Boot with a
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