Dmitry Vyukov <dvyukov@xxxxxxxxxx> writes:
On Thu, 5 Jan 2023 at 17:45, Viacheslav Dubeyko <slava@xxxxxxxxxxx> wrote:
On Wed, Jan 04, 2023 at 08:37:16PM -0800, Viacheslav Dubeyko wrote:
Also, as far as I can see, available volume in report (mount_0.gz) somehow corrupted already:
Syzbot generates deliberately-corrupted (aka fuzzed) filesystem images.
So basically, you can't trust anything you read from the disc.
If the volume has been deliberately corrupted, then no guarantee that file system
driver will behave nicely. Technically speaking, inode write operation should never
happened for corrupted volume because the corruption should be detected during
b-tree node initialization time. If we would like to achieve such nice state of HFS/HFS+
drivers, then it requires a lot of refactoring/implementation efforts. I am not sure that
it is worth to do because not so many guys really use HFS/HFS+ as the main file
system under Linux.
Most popular distros will happily auto-mount HFS/HFS+ from anything
inserted into USB (e.g. what one may think is a charger). This creates
interesting security consequences for most Linux users.
An image may also be corrupted non-deliberately, which will lead to
random memory corruptions if the kernel trusts it blindly.
I am going to point out that there are no known linux filesystems
that are safe to mount when someone has written a deliberately
corrupted filesystem on a usb stick.
Some filesystems like ext4 make a best effort to fix bugs of this sort
as they are discovered but unless something has changed since last I
looked no one makes the effort to ensure that it is 100% safe to mount
any possible corrupted version of any Linux filesystem.
If there is any filesystem in Linux that is safe to automount from
an untrusted USB stick I really would like to hear about it. We could
allow mounting them in unprivileged user namespaces and give all kinds
of interesting capabilities to our users.
As it is I respectfully suggest that if there is a security issue it is
the userspace code that automounts any filesystem on an untrusted USB
stick.
Eric
