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 12:00:57 +0800 |
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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?
> > 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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