Parsing Non linear packet payload in TC BPF programs


deepankur.gupta.97@...
 

Hi all,

We are parsing DHCP packets in TC egress program, In our case, the packet after the UDP header was not present in between skb->data and skb->data_end. On further investigation we found that it lies in non-linear portion. and we have bpf_skb_pull_data(skb,len) to direct access non-linear data.

Few questions based on above:

1. After call to bpf_skb_pull_data(skb, skb->len); the value of  skb->data and skb->data_end pointers changed. Can there be any implication down the stack with change in value of skb->data pointer. Also is this helper function analogous to skb_pull which changes the skb->data pointer and is typically moved when the packet goes up the stack as a result of packet being parsed on that layer? Do we have something similar to skb_linearize() in BPF or any other way to parse non-linear portion?

2. For our case, packet after the UDP header was in non-linear portion, can it happen that packet after IP header go in non-linear or packet after ethernet-header?

 

Regards,

Deepankur

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