On Tue, 18 Aug 2020 at 16:04, Björn Töpel <bjorn.topel@xxxxxxxxx> wrote:
>
> On Fri, 17 Jul 2020 at 08:24, Li RongQing <lirongqing@xxxxxxxxx> wrote:
> >
> > This fixes ice/i40e/ixgbe/ixgbevf_rx_buffer_flip in
> > copy mode xdp that can lead to data corruption.
> >
> > I split two patches, since i40e/xgbe/ixgbevf supports xsk
> > receiving from 4.18, put their fixes in a patch
> >
>
> Li, sorry for the looong latency. I took a looong vacation. :-P
>
> Thanks for taking a look at this, but I believe this is not a bug.
>
Ok, dug a bit more into this. I had an offlist discussion with Li, and
there are two places (AFAIK) where Li experience a BUG() in
tcp_collapse():
BUG_ON(offset < 0);
and
if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
BUG();
(Li, please correct me if I'm wrong.)
I still claim that the page-flipping mechanism is correct, but I found
some weirdness in the build_skb() call.
In drivers/net/ethernet/intel/i40e/i40e_txrx.c, build_skb() is invoked as:
skb = build_skb(xdp->data_hard_start, truesize);
For the setup Li has truesize is 2048 (half a page), but the
rx_buf_len is 1536. In the driver a packet is layed out as:
| padding 192 | packet data 1536 | skb shared info 320 |
build_skb() assumes that the second argument (frag_size) is max packet
size + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)). In other words,
frag_size should not include the padding (192 above). In build_skb(),
frag_size is used to compute the skb truesize and skb end. i40e passes
a too large buffer, and can therefore potentially corrupt the skb, and
maybe this is the reason for tcp_collapse() splatting.
Li, could you test if you get the splat with this patch:
diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
index 3e5c566ceb01..acfb4ad9b506 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
@@ -2065,7 +2065,8 @@ static struct sk_buff *i40e_build_skb(struct
i40e_ring *rx_ring,
{
unsigned int metasize = xdp->data - xdp->data_meta;
#if (PAGE_SIZE < 8192)
- unsigned int truesize = i40e_rx_pg_size(rx_ring) / 2;
+ unsigned int truesize = rx_ring->rx_buf_len +
+ SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
#else
unsigned int truesize = SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) +
SKB_DATA_ALIGN(xdp->data_end -
I'll have a look in the other Intel drivers, and see if there are
similar issues. I'll cook a patch.
Björn
