From: Ilias Apalodimas <ilias.apalodimas@linaro.org>
To: Yunsheng Lin <linyunsheng@huawei.com>
Cc: Networking <netdev@vger.kernel.org>,
Alexander Duyck <alexanderduyck@fb.com>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Alexander Lobakin <alobakin@pm.me>,
Jonathan Lemon <jonathan.lemon@gmail.com>,
Willem de Bruijn <willemb@google.com>,
Miaohe Lin <linmiaohe@huawei.com>,
Guillaume Nault <gnault@redhat.com>,
Cong Wang <cong.wang@bytedance.com>,
Jesper Dangaard Brouer <brouer@redhat.com>,
Matteo Croce <mcroce@microsoft.com>,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/1 v2] skbuff: Fix a potential race while recycling page_pool packets
Date: Thu, 15 Jul 2021 13:38:07 +0300 [thread overview]
Message-ID: <CAC_iWjLfsvr_Z2te=ABfEAecAOkQBiu22QZ8GhorA4MYnt4Uxg@mail.gmail.com> (raw)
In-Reply-To: <CAC_iWjLypqTGMxw_1ng1H8r5Yiv83G3yxUW8T1863XzFM-ShpA@mail.gmail.com>
On Thu, 15 Jul 2021 at 13:00, Ilias Apalodimas
<ilias.apalodimas@linaro.org> wrote:
>
> On Thu, 15 Jul 2021 at 07:01, Yunsheng Lin <linyunsheng@huawei.com> wrote:
> >
> > On 2021/7/9 14:29, Ilias Apalodimas wrote:
> > > As Alexander points out, when we are trying to recycle a cloned/expanded
> > > SKB we might trigger a race. The recycling code relies on the
> > > pp_recycle bit to trigger, which we carry over to cloned SKBs.
> > > If that cloned SKB gets expanded or if we get references to the frags,
> > > call skbb_release_data() and overwrite skb->head, we are creating separate
> > > instances accessing the same page frags. Since the skb_release_data()
> > > will first try to recycle the frags, there's a potential race between
> > > the original and cloned SKB, since both will have the pp_recycle bit set.
> > >
> > > Fix this by explicitly those SKBs not recyclable.
> > > The atomic_sub_return effectively limits us to a single release case,
> > > and when we are calling skb_release_data we are also releasing the
> > > option to perform the recycling, or releasing the pages from the page pool.
> > >
> > > Fixes: 6a5bcd84e886 ("page_pool: Allow drivers to hint on SKB recycling")
> > > Reported-by: Alexander Duyck <alexanderduyck@fb.com>
> > > Suggested-by: Alexander Duyck <alexanderduyck@fb.com>
> > > Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> > > ---
> > > Changes since v1:
> > > - Set the recycle bit to 0 during skb_release_data instead of the
> > > individual fucntions triggering the issue, in order to catch all
> > > cases
> > > net/core/skbuff.c | 4 +++-
> > > 1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > > index 12aabcda6db2..f91f09a824be 100644
> > > --- a/net/core/skbuff.c
> > > +++ b/net/core/skbuff.c
> > > @@ -663,7 +663,7 @@ static void skb_release_data(struct sk_buff *skb)
> > > if (skb->cloned &&
> > > atomic_sub_return(skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1,
> > > &shinfo->dataref))
> > > - return;
> > > + goto exit;
> >
> > Is it possible this patch may break the head frag page for the original skb,
> > supposing it's head frag page is from the page pool and below change clears
> > the pp_recycle for original skb, causing a page leaking for the page pool?
> >
>
> So this would leak eventually dma mapping if the skb is cloned (and
> the dataref is now +1) and we are freeing the original skb first?
>
Apologies for the noise, my description was not complete.
The case you are thinking is clone an SKB and then expand the original?
thanks
/Ilias
> > >
> > > skb_zcopy_clear(skb, true);
> > >
> > > @@ -674,6 +674,8 @@ static void skb_release_data(struct sk_buff *skb)
> > > kfree_skb_list(shinfo->frag_list);
> > >
> > > skb_free_head(skb);
> > > +exit:
> > > + skb->pp_recycle = 0;
> > > }
> > >
> > > /*
> > >
next prev parent reply other threads:[~2021-07-15 10:38 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-09 6:29 [PATCH 1/1 v2] skbuff: Fix a potential race while recycling page_pool packets Ilias Apalodimas
2021-07-09 14:34 ` Alexander Duyck
2021-07-09 17:29 ` Ilias Apalodimas
2021-07-12 11:52 ` Jesper Dangaard Brouer
2021-07-15 4:00 ` Yunsheng Lin
2021-07-15 10:00 ` Ilias Apalodimas
2021-07-15 10:38 ` Ilias Apalodimas [this message]
2021-07-15 10:47 ` Yunsheng Lin
2021-07-15 12:37 ` Ilias Apalodimas
2021-07-15 14:25 ` Alexander Duyck
2021-07-15 14:45 ` Ilias Apalodimas
2021-07-15 14:57 ` Alexander Duyck
2021-07-15 15:02 ` Ilias Apalodimas
2021-07-16 2:30 ` Yunsheng Lin
2021-07-16 6:43 ` Ilias Apalodimas
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