Messages in this thread | | | Subject | Re: [PATCH net] net: gro: set the last skb->next to NULL when it get merged | From | Yunsheng Lin <> | Date | Wed, 27 Oct 2021 20:40:35 +0800 |
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On 2021/10/27 16:56, Jason Xing wrote: > On Wed, Oct 27, 2021 at 4:07 PM Jason Xing <kerneljasonxing@gmail.com> wrote: >> >> On Wed, Oct 27, 2021 at 3:23 PM Jason Xing <kerneljasonxing@gmail.com> wrote: >>> >>> On Tue, Oct 26, 2021 at 9:19 PM <kerneljasonxing@gmail.com> wrote: >>>> >>>> From: Jason Xing <xingwanli@kuaishou.com> >>>> >>>> Setting the @next of the last skb to NULL to prevent the panic in future >>>> when someone does something to the last of the gro list but its @next is >>>> invalid. >>>> >>>> For example, without the fix (commit: ece23711dd95), a panic could happen >>>> with the clsact loaded when skb is redirected and then validated in >>>> validate_xmit_skb_list() which could access the error addr of the @next >>>> of the last skb. Thus, "general protection fault" would appear after that. >>>> >>>> Signed-off-by: Jason Xing <xingwanli@kuaishou.com> >>>> --- >>>> net/core/skbuff.c | 1 + >>>> 1 file changed, 1 insertion(+) >>>> >>>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c >>>> index 2170bea..7b248f1 100644 >>>> --- a/net/core/skbuff.c >>>> +++ b/net/core/skbuff.c >>>> @@ -4396,6 +4396,7 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb) >>>> skb_shinfo(p)->frag_list = skb; >>>> else >>>> NAPI_GRO_CB(p)->last->next = skb; >>>> + skb->next = NULL; >>>> NAPI_GRO_CB(p)->last = skb; >>> >>> Besides, I'm a little bit confused that this operation inserts the >>> newest skb into the tail of the flow, so the tail of flow is the >>> newest, head oldest. The patch (commit: 600adc18) introduces the flush >>> of the oldest when the flow is full to lower the latency, but actually >>> it fetches the tail of the flow. Do I get something wrong here? I feel >> >> I have to update this part. The commit 600adc18 evicts and flushes the >> oldest flow. But for the current kernel, when >> "napi->gro_hash[hash].count >= MAX_GRO_SKBS" happens, the >> gro_flush_oldest() flushes the oldest skb of one certain flow, >> actually it is the newest skb because it is at the end of the list.
it seems the below is more matched with the gro_flush_oldest() instead of the above code block: https://elixir.bootlin.com/linux/v5.15-rc3/source/net/core/dev.c#L6118
> > I just submitted another patch to explain how it happens, please help > me review both patches. > > Link: https://lore.kernel.org/lkml/20211027084944.4508-1-kerneljasonxing@gmail.com/ > > Thanks again, > Jason > >> >>> it is really odd. >>> >>> Thanks, >>> Jason >>> >>>> __skb_header_release(skb); >>>> lp = p; >>>> -- >>>> 1.8.3.1 >>>> > . >
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