Re: [PATCH] skbuff: Fix a potential race while recycling page_pool packets
From: Ilias Apalodimas
Date: Thu Jul 08 2021 - 12:31:19 EST
+cc Alexander on his gmail address since the Intel one bounced.
Alexander want me to respin it with you gmail address on the Reported-by?
Sorry for the noise
/Ilias
On Thu, 8 Jul 2021 at 19:24, Ilias Apalodimas
<ilias.apalodimas@xxxxxxxxxx> 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 that over to cloned SKBs.
> When that cloned SKB gets expanded, we are creating 2 separate instances
> accessing the 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.
>
> Fix this by explicitly making the cloned/expanded SKB not recyclable.
> If the original SKB is freed first the pages are released.
> If it is released after the clone/expended skb then it can still be
> recycled.
>
> Fixes: 6a5bcd84e886 ("page_pool: Allow drivers to hint on SKB recycling")
> Reported-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> Signed-off-by: Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx>
> ---
> net/core/skbuff.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 12aabcda6db2..0cb53c05ed76 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -1718,6 +1718,13 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
> }
> off = (data + nhead) - skb->head;
>
> + /* If it's a cloned skb we expand with frags attached we must prohibit
> + * the recycling code from running, otherwise we might trigger a race
> + * while trying to recycle the fragments from the original and cloned
> + * skb
> + */
> + if (skb_cloned(skb))
> + skb->pp_recycle = 0;
> skb->head = data;
> skb->head_frag = 0;
> skb->data += off;
> --
> 2.32.0.rc0
>