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Date: Fri, 15 Jan 2021 09:12:43 +0100
From: Steffen Klassert <steffen.klassert@...unet.com>
To: Dongseok Yi <dseok.yi@...sung.com>
CC: "David S. Miller" <davem@...emloft.net>,
<namkyu78.kim@...sung.com>, Alexander Lobakin <alobakin@...me>,
Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
Jakub Kicinski <kuba@...nel.org>,
Willem de Bruijn <willemb@...gle.com>,
<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] udp: ipv4: manipulate network header of NATed UDP
GRO fraglist
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.yi@...sung.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().
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