From: Rafael Aquini <aquini@redhat.com>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
akpm@linux-foundation.org
Subject: Re: [PATCH] mm: swapfile: avoid split_swap_cluster() NULL pointer dereference
Date: Wed, 23 Sep 2020 00:34:59 -0400 [thread overview]
Message-ID: <20200923043459.GL795820@optiplex-lnx> (raw)
In-Reply-To: <878sd1qllb.fsf@yhuang-dev.intel.com>
On Wed, Sep 23, 2020 at 10:21:36AM +0800, Huang, Ying wrote:
> Hi, Rafael,
>
> Rafael Aquini <aquini@redhat.com> writes:
>
> > 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.
>
> Thanks for reporting. But the bug looks strange. Because in a system
> with only HDD swap devices, during THP swap out, the swap cluster
> shouldn't be allocated, as in
>
> shrink_page_list()
> add_to_swap()
> get_swap_page()
> get_swap_pages()
> swap_alloc_cluster()
>
The underlying problem is that swap_info_struct.cluster_info is always NULL
on the rotational storage case. So, it's very easy to follow that constructions
like this one, in split_swap_cluster
...
ci = lock_cluster(si, offset);
cluster_clear_huge(ci);
...
will go for a NULL pointer dereference, in that case, given that lock_cluster
reads:
...
struct swap_cluster_info *ci;
ci = si->cluster_info;
if (ci) {
ci += offset / SWAPFILE_CLUSTER;
spin_lock(&ci->lock);
}
return ci;
...
next prev parent reply other threads:[~2020-09-23 4:35 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-22 18:48 [PATCH] mm: swapfile: avoid split_swap_cluster() NULL pointer dereference Rafael Aquini
2020-09-22 19:47 ` Andrew Morton
2020-09-23 13:42 ` Rafael Aquini
2020-09-25 2:59 ` Andrew Morton
2020-09-25 3:06 ` Huang, Ying
2020-09-25 3:10 ` Andrew Morton
2020-09-23 2:21 ` Huang, Ying
2020-09-23 4:34 ` Rafael Aquini [this message]
2020-09-23 5:13 ` Huang, Ying
2020-09-23 13:01 ` Rafael Aquini
2020-09-24 0:59 ` Huang, Ying
2020-09-24 2:09 ` Rafael Aquini
2020-09-24 3:51 ` Huang, Ying
2020-09-24 6:30 ` Rafael Aquini
2020-09-24 6:57 ` Huang, Ying
2020-09-24 7:45 ` Huang, Ying
2020-09-24 15:08 ` Rafael Aquini
2020-09-25 3:21 ` Huang, Ying
2020-09-26 15:16 ` Rafael Aquini
2020-09-27 5:33 ` Huang, Ying
2020-10-01 14:31 ` Rafael Aquini
2020-10-05 13:39 ` Rafael Aquini
2020-10-09 0:18 ` Huang, Ying
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