From: Michal Hocko <mhocko@suse.com>
To: Suren Baghdasaryan <surenb@google.com>
Cc: akpm@linux-foundation.org, ccross@google.com,
sumit.semwal@linaro.org, dave.hansen@intel.com,
keescook@chromium.org, willy@infradead.org,
kirill.shutemov@linux.intel.com, vbabka@suse.cz,
hannes@cmpxchg.org, ebiederm@xmission.com, brauner@kernel.org,
legion@kernel.org, ran.xiaokai@zte.com.cn, sashal@kernel.org,
chris.hyser@oracle.com, dave@stgolabs.net, pcc@google.com,
caoxiaofeng@yulong.com, david@redhat.com, gorcunov@gmail.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kernel-team@android.com,
syzbot+aa7b3d4b35f9dc46a366@syzkaller.appspotmail.com
Subject: Re: [PATCH v4 3/3] mm: fix use-after-free when anon vma name is used after vma is freed
Date: Wed, 23 Feb 2022 16:29:24 +0100 [thread overview]
Message-ID: <YhZS1A9wKQ8Aryin@dhcp22.suse.cz> (raw)
In-Reply-To: <CAJuCfpE+dpCmA6sRQJBanRP2uJiQHGdoGGjvkhL_GqxRdY9aCg@mail.gmail.com>
On Wed 23-02-22 06:10:54, Suren Baghdasaryan wrote:
> On Wed, Feb 23, 2022 at 12:55 AM Michal Hocko <mhocko@suse.com> wrote:
> >
> > On Tue 22-02-22 07:43:40, Suren Baghdasaryan wrote:
> > > On Tue, Feb 22, 2022 at 12:06 AM Michal Hocko <mhocko@suse.com> wrote:
> > > >
> > > > On Mon 21-02-22 21:40:25, Suren Baghdasaryan wrote:
> > > > > When adjacent vmas are being merged it can result in the vma that was
> > > > > originally passed to madvise_update_vma being destroyed. In the current
> > > > > implementation, the name parameter passed to madvise_update_vma points
> > > > > directly to vma->anon_name->name and it is used after the call to
> > > > > vma_merge. In the cases when vma_merge merges the original vma and
> > > > > destroys it, this will result in use-after-free bug as shown below:
> > > > >
> > > > > madvise_vma_behavior << passes vma->anon_name->name as name param
> > > > > madvise_update_vma(name)
> > > > > vma_merge
> > > > > __vma_adjust
> > > > > vm_area_free <-- frees the vma
> > > > > replace_vma_anon_name(name) <-- UAF
> > > >
> > > > This seems to be stale because bare const char pointer is not passed in
> > > > the call chain. In fact I am not even sure there is any actual UAF here
> > > > after the rework.
> > > > Could you be more specific in describing the scenario?
> > >
> > > Yes, sorry, I need to update the part of the description talking about
> > > passing vma->anon_name->name directly.
> > > I think UAF is still there, it's just harder to reproduce (admittedly
> > > I could not reproduce it with the previous reproducer). The scenario
> > > would be when a vma with vma->anon_name->kref == 1 is being merged
> > > with another one and freed in the process:
> > >
> > > madvise_vma_behavior
> > > anon_name = vma_anon_name(vma) <-- does not increase refcount
> > > madvise_update_vma(anon_name)
> > > *prev = vma_merge <-- returns another vma
> > > __vma_adjust
> > > vm_area_free(vma)
> > > free_vma_anon_name
> > > anon_vma_name_put
> > > vma_anon_name_free <-- frees the vma->anon_name
> > > vma = *prev <-- original vma was freed
> >
> > How come this is not a UAF in the first place?
>
> Sorry, I got you confused. The original vma that was passed as a
> parameter to vma_merge(vma) was freed and vma_merge() returns the area
> it was merged with:
>
> *prev = vma_merge(vma_a) <-- vma_a is merged with adjacent vma_b,
> vma_a is freed and vma_b is returned
> vma = *prev <-- "vma" now points to vma_b
OK, I see the problem now. Essentially if we have two adjacent vmas
which have the same name but wrapped by two anon_vma_name instances
and we merge them together then the first one can be freed along with
its anon_vma_name which is still used by replace_anon_vma_name.
Thanks for the patience.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2022-02-23 15:29 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-22 5:40 [PATCH 1/3] mm: refactor vm_area_struct::anon_vma_name usage code Suren Baghdasaryan
2022-02-22 5:40 ` [PATCH 2/3] mm: prevent vm_area_struct::anon_name refcount saturation Suren Baghdasaryan
2022-02-22 9:17 ` Michal Hocko
2022-02-22 15:56 ` Suren Baghdasaryan
2022-02-23 3:02 ` Suren Baghdasaryan
2022-02-23 8:26 ` Michal Hocko
2022-02-22 5:40 ` [PATCH v4 3/3] mm: fix use-after-free when anon vma name is used after vma is freed Suren Baghdasaryan
2022-02-22 5:41 ` Suren Baghdasaryan
2022-02-22 8:06 ` Michal Hocko
2022-02-22 15:43 ` Suren Baghdasaryan
2022-02-23 8:55 ` Michal Hocko
2022-02-23 14:10 ` Suren Baghdasaryan
2022-02-23 15:29 ` Michal Hocko [this message]
2022-02-23 15:38 ` Suren Baghdasaryan
2022-02-22 8:51 ` [PATCH 1/3] mm: refactor vm_area_struct::anon_vma_name usage code Michal Hocko
2022-02-22 15:51 ` Suren Baghdasaryan
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