Re: [PATCH] mm: swapfile: avoid split_swap_cluster() NULL pointer dereference

[Rafael Aquini]

On Tue, Sep 22, 2020 at 12:47:50PM -0700, Andrew Morton wrote:
> On Tue, 22 Sep 2020 14:48:38 -0400 Rafael Aquini <aquini@xxxxxxxxxx> wrote:
> 
> > The swap area descriptor only gets struct swap_cluster_info *cluster_info
> > allocated if the swapfile is backed by non-rotational storage.
> > When the swap area is laid on top of ordinary disk spindles, lock_cluster()
> > will naturally return NULL.
> > 
> > CONFIG_THP_SWAP exposes cluster_info infrastructure to a broader number of
> > use cases, and split_swap_cluster(), which is the counterpart of split_huge_page()
> > for the THPs in the swapcache, misses checking the return of lock_cluster before
> > operating on the cluster_info pointer.
> > 
> > This patch addresses that issue by adding a proper check for the pointer
> > not being NULL in the wrappers cluster_{is,clear}_huge(), in order to avoid
> > crashes similar to the one below:
> > 
> > ...
> >
> > Fixes: 59807685a7e77 ("mm, THP, swap: support splitting THP for THP swap out")
> > Signed-off-by: Rafael Aquini <aquini@xxxxxxxxxx>
> 
> Did you consider cc:stable?
>

UGH! I missed adding it to my cc list. Shall I just forward it, now, or
do you prefer a fresh repost?