[PATCH v4] net: fix segmentation of forwarding fraglist GRO

[Willem de Bruijn]

[PATCH net v4]

Jibin Zhang wrote:
> This patch enhances GSO segment handling by properly checking
> the SKB_GSO_DODGY flag for frag_list GSO packets, addressing
> low throughput issues observed when a station accesses IPv4
> servers via hotspots with an IPv6-only upstream interface.
> 
> Specifically, it fixes a bug in GSO segmentation when forwarding
> GRO packets containing a frag_list. The function skb_segment_list
> cannot correctly process GRO skbs that have been converted by XLAT,
> since XLAT only translates the header of the head skb. Consequently,
> skbs in the frag_list may remain untranslated, resulting in protocol
> inconsistencies and reduced throughput.
> 
> To address this, the patch explicitly sets the SKB_GSO_DODGY flag
> for GSO packets in XLAT's IPv4/IPv6 protocol translation helpers
> (bpf_skb_proto_4_to_6 and bpf_skb_proto_6_to_4). This marks GSO
> packets as potentially modified after protocol translation. As a
> result, GSO segmentation will avoid using skb_segment_list and
> instead falls back to skb_segment for packets with the SKB_GSO_DODGY
> flag. This ensures that only safe and fully translated frag_list
> packets are processed by skb_segment_list, resolving protocol
> inconsistencies and improving throughput when forwarding GRO packets
> converted by XLAT.

Fixes: 9fd1ff5d2ac7 ("udp: Support UDP fraglist GRO/GSO.")
Cc: stable at vger.kernel.org