# \[PATCH\] net: fix setting csum\_start in skb\_segment()

- From: Eric Dumazet \<hidden\>
- Date: 2014-06-25 19:51:08 
- List: netdev
- Page: https://ratatoskr.run/netdev/2014/06/4281315
- Thread: https://ratatoskr.run/netdev/2014/06/4280607/t.md

```text
From: Tom Herbert <redacted>

Dave Jones reported that a crash is occurring in

csum_partial
tcp_gso_segment
inet_gso_segment
? update_dl_migration
skb_mac_gso_segment
__skb_gso_segment
dev_hard_start_xmit
sch_direct_xmit
__dev_queue_xmit
? dev_hard_start_xmit
dev_queue_xmit
ip_finish_output
? ip_output
ip_output
ip_forward_finish
ip_forward
ip_rcv_finish
ip_rcv
__netif_receive_skb_core
? __netif_receive_skb_core
? trace_hardirqs_on
__netif_receive_skb
netif_receive_skb_internal
napi_gro_complete
? napi_gro_complete
dev_gro_receive
? dev_gro_receive
napi_gro_receive

It looks like a likely culprit is that SKB_GSO_CB()->csum_start is
not set correctly when doing non-scatter gather. We are using
offset as opposed to doffset.

Reported-by: Dave Jones <redacted>
Tested-by: Dave Jones <redacted>
Signed-off-by: Tom Herbert <redacted>
Signed-off-by: Eric Dumazet <redacted>
Fixes: 7e2b10c1e52ca ("net: Support for multiple checksums with gso")
---
 net/core/skbuff.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 9cd5344fad73..c1a33033cbe2 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2993,7 +2993,7 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
 							    skb_put(nskb, len),
 							    len, 0);
 			SKB_GSO_CB(nskb)->csum_start =
-			    skb_headroom(nskb) + offset;
+			    skb_headroom(nskb) + doffset;
 			continue;
 		}
 
```