Messages in this thread | | | Subject | Re: [PATCH 1/1 v2] skbuff: Fix a potential race while recycling page_pool packets | From | Yunsheng Lin <> | Date | Thu, 15 Jul 2021 18:47:55 +0800 |
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On 2021/7/15 18:38, Ilias Apalodimas wrote: > 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?
Yes. It seems we might need different pp_recycle bit for head frag and data frag.
> > 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; >>>> } >>>> >>>> /* >>>> > . >
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