On Saturday, July 22, 2023 2:01:34 AM EDT 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.
A while back, I wrote the fsfuzzer specifically to find, in a repeatable way,
filesystem bugs so they can be fixed:
https://github.com/stevegrubb/fsfuzzer
It does not support all filesystems, but it is easy to add support through
adding the correct mounter to the scrips. It has found *so* *many* filesystem
bugs over time.
-Steve
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