linux-kernel - Re: [PATCH 1/1] mm: fix use-after-free bug when mm->mmap is reused after being freed

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Date:   Tue, 15 Feb 2022 12:46:57 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Michal Hocko <mhocko@...nel.org>, Michal Hocko <mhocko@...e.com>,
        Yang Shi <shy828301@...il.com>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <guro@...com>, Rik van Riel <riel@...riel.com>,
        Minchan Kim <minchan@...nel.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Christian Brauner <brauner@...nel.org>,
        Christian Brauner <christian@...uner.io>,
        Christoph Hellwig <hch@...radead.org>,
        Oleg Nesterov <oleg@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Jann Horn <jannh@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Florian Weimer <fweimer@...hat.com>,
        Jan Engelhardt <jengelh@...i.de>,
        Tim Murray <timmurray@...gle.com>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-team <kernel-team@...roid.com>,
        syzbot <syzbot+2ccf63a4bd07cf39cab0@...kaller.appspotmail.com>
Subject: Re: [PATCH 1/1] mm: fix use-after-free bug when mm->mmap is reused
 after being freed

On Tue, Feb 15, 2022 at 12:45 PM Suren Baghdasaryan <surenb@...gle.com> wrote:
>
> On Tue, Feb 15, 2022 at 12:37 PM Andrew Morton
> <akpm@...ux-foundation.org> wrote:
> >
> > On Tue, 15 Feb 2022 12:19:22 -0800 Suren Baghdasaryan <surenb@...gle.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);
> > >  }
> >
> > https://lore.kernel.org/all/00000000000072ef2c05d7f81950@google.com/
> >
> > It would be nice to have a Fixes: for this.
>
> Oh, right. Should be:
>
> Fixes: 64591e8605d6 ("mm: protect free_pgtables with mmap_lock write
> lock in exit_mmap")

Andrew, do you want me to post another version with Fixes:
64591e8605d6 ("mm: protect free_pgtables with mmap_lock write lock in
exit_mmap") added or you can add it directly?


>
> >
> > Is it specific to process_mrelease(), or should we backport further?
>
> The broken change is recent and was introduced in v5.17-rc1.