Re: [PATCH v2 2/2] fuse: remove tmp folio for writebacks and internal rb tree

[Miklos Szeredi <miklos@szeredi.hu>]

On Wed, 16 Oct 2024 at 11:44, Jingbo Xu <jefflexu@linux.alibaba.com> wrote:

> 1) a non-malicious fuse daemon wants to allocate some memory when
> processing a fuse request, which in turn leads to memory reclaim and
> thus waiting on the writeback of fuse dirty pages - a deadlock here.
> This is reasonable and also the target scenario that this series wants
> to fix.
>
> 2) a malicious fuse daemon refuses to process any request; or a buggy or
> not well-written fuse daemon as you described, e.g. may call sync(2)
> itself or access page cache backed by itself, then
>   2.1) any unrelated user process attempting to initiate a sync(2)
> itself, will hang there.  This scenario is also unexpected and shall be
> fixed.

Exactly.

We only care about

 - properly written server not deadlocking

 - buggy or malicious server not denying service to unrelated tasks,
where unrelated means it would not otherwise be able to access the
fuse mount. Typically this separation is done with a user namespace or
-oallow_other.

Thanks,
Miklos


>   2.2) any direct user of fuse filesystem (e.g. access files backed by
> fuse filesystem) will hang in this case.  IMHO this is expected, and the
> impact is affordable as it is controlled within certain range (the
> direct user of the fs).
>
> --
> Thanks,
> Jingbo