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Date:   Fri, 25 Feb 2022 11:17:34 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Suren Baghdasaryan <surenb@google.com>, shy828301@gmail.com,
        rientjes@google.com, willy@infradead.org, hannes@cmpxchg.org,
        guro@fb.com, riel@surriel.com, minchan@kernel.org,
        kirill@shutemov.name, aarcange@redhat.com, brauner@kernel.org,
        christian@brauner.io, hch@infradead.org, oleg@redhat.com,
        david@redhat.com, jannh@google.com, shakeelb@google.com,
        luto@kernel.org, christian.brauner@ubuntu.com, fweimer@redhat.com,
        jengelh@inai.de, timmurray@google.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, kernel-team@android.com,
        syzbot+2ccf63a4bd07cf39cab0@syzkaller.appspotmail.com,
        Liam Howlett <liam.howlett@oracle.com>
Subject: Re: [PATCH 1/1] mm: fix use-after-free bug when mm->mmap is reused
 after being freed
Message-ID: <YhisviDOip+axLDe@dhcp22.suse.cz>
References: <20220215201922.1908156-1-surenb@google.com>
 <20220224201859.a38299b6c9d52cb51e6738ea@linux-foundation.org>
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On Thu 24-02-22 20:18:59, Andrew Morton wrote:
> On Tue, 15 Feb 2022 12:19:22 -0800 Suren Baghdasaryan <surenb@google.com> wrote:
> 
> > After exit_mmap frees all vmas in the mm, mm->mmap needs to be reset,
> > otherwise it points to a vma that was freed and when reused leads to
> > a use-after-free bug.
> > 
> > ...
> >
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -3186,6 +3186,7 @@ void exit_mmap(struct mm_struct *mm)
> >  		vma = remove_vma(vma);
> >  		cond_resched();
> >  	}
> > +	mm->mmap = NULL;
> >  	mmap_write_unlock(mm);
> >  	vm_unacct_memory(nr_accounted);
> >  }
> 
> After the Maple tree patches, mm_struct.mmap doesn't exist.  So I'll
> revert this fix as part of merging the maple-tree parts of linux-next.
> I'll be sending this fix to Linus this week.

But this is a regression introduced in this release cycle so the patch
should be merged before Maple tree patches, no?
-- 
Michal Hocko
SUSE Labs