[PATCH net] virtio-net: fix for skb_over_panic inside big mode

In virtio-net's large packet mode, there is a hole in the space behind
buf.

    hdr_padded_len - hdr_len

We must take this into account when calculating tailroom.

[   44.544385] skb_put.cold (net/core/skbuff.c:5254 (discriminator 1) net/core/skbuff.c:5252 (discriminator 1))
[   44.544864] page_to_skb (drivers/net/virtio_net.c:485) [   44.545361] receive_buf (drivers/net/virtio_net.c:849 drivers/net/virtio_net.c:1131)
[   44.545870] ? netif_receive_skb_list_internal (net/core/dev.c:5714)
[   44.546628] ? dev_gro_receive (net/core/dev.c:6103)
[   44.547135] ? napi_complete_done (./include/linux/list.h:35 net/core/dev.c:5867 net/core/dev.c:5862 net/core/dev.c:6565)
[   44.547672] virtnet_poll (drivers/net/virtio_net.c:1427 drivers/net/virtio_net.c:1525)
[   44.548251] __napi_poll (net/core/dev.c:6985)
[   44.548744] net_rx_action (net/core/dev.c:7054 net/core/dev.c:7139)
[   44.549264] __do_softirq (./arch/x86/include/asm/jump_label.h:19 ./include/linux/jump_label.h:200 ./include/trace/events/irq.h:142 kernel/softirq.c:560)
[   44.549762] irq_exit_rcu (kernel/softirq.c:433 kernel/softirq.c:637 kernel/softirq.c:649)
[   44.551384] common_interrupt (arch/x86/kernel/irq.c:240 (discriminator 13))
[   44.551991] ? asm_common_interrupt (./arch/x86/include/asm/idtentry.h:638)
[   44.552654] asm_common_interrupt (./arch/x86/include/asm/idtentry.h:638)

Fixes: fb32856b16ad ("virtio-net: page_to_skb() use build_skb when there's sufficient tailroom")
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Reported-by: Corentin Noël <redacted>
Tested-by: Corentin Noël <redacted>
---
 drivers/net/virtio_net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index fa407eb8b457..78a01c71a17c 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -406,7 +406,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 	 * add_recvbuf_mergeable() + get_mergeable_buf_len()
 	 */
 	truesize = headroom ? PAGE_SIZE : truesize;
-	tailroom = truesize - len - headroom;
+	tailroom = truesize - len - headroom - (hdr_padded_len - hdr_len);
 	buf = p - headroom;
 
 	len -= hdr_len;

-- 
2.31.0

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Fri,  4 Jun 2021 01:09:01 +0800 you wrote:

In virtio-net's large packet mode, there is a hole in the space behind
buf.

    hdr_padded_len - hdr_len

We must take this into account when calculating tailroom.

[...]

Here is the summary with links:
  - [net] virtio-net: fix for skb_over_panic inside big mode
    https://git.kernel.org/netdev/net/c/1a8024239dac

You are awesome, thank you!
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在 2021/6/4 上午1:09, Xuan Zhuo 写道:

In virtio-net's large packet mode, there is a hole in the space behind
buf.

before the buf actually or behind the vnet header?

The patch looks correct and I saw it has been merged.

But I prefer to do that in receive_big() instead of here.

Thanks

  	buf = p - headroom;
  
  	len -= hdr_len;