linux-kernel - Re: [PATCH v2 1/1] mm: fix use-after-free when anon vma name is used after vma is freed

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Message-ID: <CAJuCfpGhWh95wxRxy35d4jbCGUdCyasYQBs7DG2fVn34tSXrRQ@mail.gmail.com>
Date:   Thu, 10 Feb 2022 07:21:52 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Colin Cross <ccross@...gle.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Michal Hocko <mhocko@...e.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Kees Cook <keescook@...omium.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, brauner@...nel.org,
        legion@...nel.org, ran.xiaokai@....com.cn, sashal@...nel.org,
        Chris Hyser <chris.hyser@...cle.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Peter Collingbourne <pcc@...gle.com>, caoxiaofeng@...ong.com,
        David Hildenbrand <david@...hat.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-team <kernel-team@...roid.com>,
        syzbot+aa7b3d4b35f9dc46a366@...kaller.appspotmail.com
Subject: Re: [PATCH v2 1/1] mm: fix use-after-free when anon vma name is used
 after vma is freed

On Thu, Feb 10, 2022 at 5:27 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Wed, Feb 09, 2022 at 08:32:15PM -0800, Suren Baghdasaryan wrote:
> > +void vma_anon_name_put(struct anon_vma_name *anon_name)
> > +{
> > +     kref_put(&anon_name->kref, vma_anon_name_free);
> > +}
>
> To agree with Michal, make this:
>
>         if (anon_name)
>                 kref_put(&anon_name->kref, vma_anon_name_free);

Ack.

>
> >
> > -     error = madvise_update_vma(vma, prev, start, end, new_flags,
> > -                                vma_anon_name(vma));
> > +     anon_name = vma_anon_name_get(vma);
> > +     if (anon_name) {
> > +             error = madvise_update_vma(vma, prev, start, end, new_flags,
> > +                                        anon_name->name);
> > +             vma_anon_name_put(anon_name);
> > +     } else {
> > +             error = madvise_update_vma(vma, prev, start, end, new_flags,
> > +                                        NULL);
> > +     }
>
> And then this becomes:
>
>         anon_name = vma_anon_name_get(vma);
>         error = madvise_update_vma(vma, prev, start, end, new_flags, anon_name);
>         vma_anon_name_put(anon_name);

As I indicated in the other reply, there is another madvise_update_vma
user which has only the name string, not the anon_vma_name struct. So
this can become:

   anon_name = vma_anon_name_get(vma);
   error = madvise_update_vma(vma, prev, start, end, new_flags,
                                                   anon_name ?
anon_name->name : NULL);
   vma_anon_name_put(anon_name);