On Fri, Jan 15, 2021 at 02:58:24PM +0900, Dongseok Yi wrote: > UDP/IP header of UDP GROed frag_skbs are not updated even after NAT > forwarding. Only the header of head_skb from ip_finish_output_gso -> > skb_gso_segment is updated but following frag_skbs are not updated. > > A call path skb_mac_gso_segment -> inet_gso_segment -> > udp4_ufo_fragment -> __udp_gso_segment -> __udp_gso_segment_list > does not try to update UDP/IP header of the segment list.
We still need to find out why it works for Alexander, but not for you. Different usecases? We copy only the MAC header in skb_segment_list(), so I think this is a valid bug when NAT changed the UDP header. > > Update dport, daddr and checksums of each skb of the segment list > after __udp_gso_segment. > > Fixes: 9fd1ff5d2ac7 (udp: Support UDP fraglist GRO/GSO.) > Signed-off-by: Dongseok Yi <dseok...@samsung.com> > --- > Steffen Klassert said, there could be 2 options. > https://lore.kernel.org/patchwork/patch/1362257/ > > I was trying to write a quick fix, but it was not easy to forward > segmented list. Currently, assuming DNAT only. Should we consider > SNAT too? If it is broken, then it is broken for both, so yes. > > net/ipv4/udp_offload.c | 45 +++++++++++++++++++++++++++++++++++++++++---- > 1 file changed, 41 insertions(+), 4 deletions(-) > > diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c > index ff39e94..7e24928 100644 > --- a/net/ipv4/udp_offload.c > +++ b/net/ipv4/udp_offload.c > @@ -309,10 +309,12 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff > *skb, > netdev_features_t features) > { > struct sk_buff *segs = ERR_PTR(-EINVAL); > + struct sk_buff *seg; > unsigned int mss; > __wsum csum; > - struct udphdr *uh; > - struct iphdr *iph; > + struct udphdr *uh, *uh2; > + struct iphdr *iph, *iph2; > + bool is_fraglist = false; > > if (skb->encapsulation && > (skb_shinfo(skb)->gso_type & > @@ -327,8 +329,43 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff > *skb, > if (!pskb_may_pull(skb, sizeof(struct udphdr))) > goto out; > > - if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4) > - return __udp_gso_segment(skb, features); > + if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4) { > + if (skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST) > + is_fraglist = true; > + > + segs = __udp_gso_segment(skb, features); > + if (IS_ERR_OR_NULL(segs) || !is_fraglist) > + return segs; > + > + seg = segs; > + uh = udp_hdr(seg); > + iph = ip_hdr(seg); > + > + while ((seg = seg->next)) { > + uh2 = udp_hdr(seg); > + iph2 = ip_hdr(seg); > + > + if (uh->dest == uh2->dest && iph->daddr == iph2->daddr) > + continue; > + > + if (uh2->check) { > + inet_proto_csum_replace4(&uh2->check, seg, > + iph2->daddr, > + iph->daddr, true); > + inet_proto_csum_replace2(&uh2->check, seg, > + uh2->dest, uh->dest, > + false); > + if (!uh2->check) > + uh2->check = CSUM_MANGLED_0; > + } > + uh2->dest = uh->dest; > + > + csum_replace4(&iph2->check, iph2->daddr, iph->daddr); > + iph2->daddr = iph->daddr; > + } > + > + return segs; > + } I would not like to add this to a generic codepath. I think we can relatively easy copy the full headers in skb_segment_list(). I think about something like the (completely untested) patch below: diff --git a/net/core/skbuff.c b/net/core/skbuff.c index f62cae3f75d8..63ae7f79fad7 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -3651,13 +3651,14 @@ struct sk_buff *skb_segment_list(struct sk_buff *skb, unsigned int offset) { struct sk_buff *list_skb = skb_shinfo(skb)->frag_list; + unsigned int doffset = skb->data - skb_mac_header(skb); unsigned int tnl_hlen = skb_tnl_header_len(skb); unsigned int delta_truesize = 0; unsigned int delta_len = 0; struct sk_buff *tail = NULL; struct sk_buff *nskb; - skb_push(skb, -skb_network_offset(skb) + offset); + skb_push(skb, doffset); skb_shinfo(skb)->frag_list = NULL; @@ -3675,7 +3676,7 @@ struct sk_buff *skb_segment_list(struct sk_buff *skb, delta_len += nskb->len; delta_truesize += nskb->truesize; - skb_push(nskb, -skb_network_offset(nskb) + offset); + skb_push(nskb, doffset); skb_release_head_state(nskb); __copy_skb_header(nskb, skb); diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c index ff39e94781bf..1181398378b8 100644 --- a/net/ipv4/udp_offload.c +++ b/net/ipv4/udp_offload.c @@ -190,9 +190,22 @@ EXPORT_SYMBOL(skb_udp_tunnel_segment); static struct sk_buff *__udp_gso_segment_list(struct sk_buff *skb, netdev_features_t features) { + struct sk_buff *list_skb = skb_shinfo(skb)->frag_list; unsigned int mss = skb_shinfo(skb)->gso_size; + unsigned int offset; - skb = skb_segment_list(skb, features, skb_mac_header_len(skb)); + skb_headers_offset_update(list_skb, skb_headroom(list_skb) - skb_headroom(skb)); + + /* Check for header changes and copy the full header in that case. */ + if ((udp_hdr(skb)->dest == udp_hdr(list_skb)->dest) && + (udp_hdr(skb)->source == udp_hdr(list_skb)->source) && + (ip_hdr(skb)->daddr == ip_hdr(list_skb)->daddr) && + (ip_hdr(skb)->saddr == ip_hdr(list_skb)->saddr)) + offset = skb_mac_header_len(skb); + else + offset = skb->data - skb_mac_header(skb); + + skb = skb_segment_list(skb, features, offset); if (IS_ERR(skb)) return skb; After that you can apply the CSUM magic in __udp_gso_segment_list().
