Re: [Lsf-pc] [LSF/MM/BPF TOPIC] Where is fuse going? API cleanup, restructuring and more

[Jan Kara <jack@suse.cz>]

On Sun 22-03-26 12:51:57, Gao Xiang wrote:
> On 2026/3/22 11:25, Demi Marie Obenour wrote:
> > > Technically speaking fuse4fs could just invoke e2fsck -fn before it
> > > starts up the rest of the libfuse initialization but who knows if that's
> > > an acceptable risk.  Also unclear if you actually want -fy for that.
> > 
> 
> Let me try to reply the remaining part:
> 
> > To me, the attacks mentioned above are all either user error,
> > or vulnerabilities in software accessing the filesystem.  If one
> 
> There are many consequences if users try to use potential inconsistent
> writable filesystems directly (without full fsck), what I can think
> out including but not limited to:
> 
>  - data loss (considering data block double free issue);
>  - data theft (for example, users keep sensitive information in the
>       workload in a high permission inode but it can be read with
>       low permission malicious inode later);
>  - data tamper (the same principle).
> 
> All vulnerabilities above happen after users try to write the
> inconsistent filesystem, which is hard to prevent by on-disk
> design.
> 
> But if users write with copy-on-write to another local consistent
> filesystem, all the vulnerabilities above won't exist.

OK, so if I understand correctly you are advocating that untrusted initial data
should be provided on immutable filesystem and any needed modification
would be handled by overlayfs (or some similar layer) and stored on
(initially empty) writeable filesystem.

That's a sensible design for usecase like containers but what started this
thread about FUSE drivers for filesystems were usecases like access to
filesystems on drives attached at USB port of your laptop. There it isn't
really practical to use your design. You need a standard writeable
filesystem for that but at the same time you cannot quite trust the content
of everything that gets attached to your USB port...

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR