Hi, On Mon, Aug 09, 2021 at 04:10:36PM +1200, Cole Dishington wrote: > Adds support for masquerading into a smaller subset of ports - > defined by the PSID values from RFC-7597 Section 5.1. This is part of > the support for MAP-E and Lightweight 4over6, which allows multiple > devices to share an IPv4 address by splitting the L4 port / id into > ranges. > > Co-developed-by: Anthony Lineham <anthony.lineham@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Anthony Lineham <anthony.lineham@xxxxxxxxxxxxxxxxxxx> > Co-developed-by: Scott Parlane <scott.parlane@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Scott Parlane <scott.parlane@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Blair Steven <blair.steven@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Cole Dishington <Cole.Dishington@xxxxxxxxxxxxxxxxxxx> > Reviewed-by: Florian Westphal <fw@xxxxxxxxx> [...] Looking at the userspace logic: https://patchwork.ozlabs.org/project/netfilter-devel/patch/20210716002219.30193-1-Cole.Dishington@xxxxxxxxxxxxxxxxxxx/ Chunk extracted from void parse_psid(...) > offset = (1 << (16 - offset_len)); Assuming offset_len = 6, then you skip 0-1023 ports, OK. > psid = psid << (16 - offset_len - psid_len); This psid calculation is correct? Maybe: psid = psid << (16 - offset_len); instead? psid=0 => 0 << (16 - 6) = 1024 psid=1 => 1 << (16 - 6) = 2048 This is implicitly assuming that 64 PSIDs are available, each of them taking 1024 ports, ie. psid_len is 6 bits. But why are you subtracting the psid_len above? > /* Handle the special case of no offset bits (a=0), so offset loops */ > min = psid; OK, this line above is the minimal port in the range > if (offset) > min += offset; ... which is incremented by the offset (to skip the 0-1023 ports). > r->min_proto.all = htons(min); > r->max_proto.all = htons(min + ((1 << (16 - offset_len - psid_len)) - 1)); Here, you subtract psid_len again, not sure why. > r->base_proto.all = htons(offset); base is set to offset, ie. 1024. > r->flags |= NF_NAT_RANGE_PSID; > r->flags |= NF_NAT_RANGE_PROTO_SPECIFIED; Now looking at the kernel side. > diff --git a/net/netfilter/nf_nat_masquerade.c b/net/netfilter/nf_nat_masquerade.c > index 8e8a65d46345..19a4754cda76 100644 > --- a/net/netfilter/nf_nat_masquerade.c > +++ b/net/netfilter/nf_nat_masquerade.c > @@ -55,8 +55,31 @@ nf_nat_masquerade_ipv4(struct sk_buff *skb, unsigned int hooknum, > newrange.flags = range->flags | NF_NAT_RANGE_MAP_IPS; > newrange.min_addr.ip = newsrc; > newrange.max_addr.ip = newsrc; > - newrange.min_proto = range->min_proto; > - newrange.max_proto = range->max_proto; > + > + if (range->flags & NF_NAT_RANGE_PSID) { > + u16 base = ntohs(range->base_proto.all); > + u16 min = ntohs(range->min_proto.all); > + u16 off = 0; > + > + /* xtables should stop base > 2^15 by enforcement of > + * 0 <= offset_len < 16 argument, with offset_len=0 > + * as a special case inwhich base=0. I don't understand this comment. > + */ > + if (WARN_ON_ONCE(base > (1 << 15))) > + return NF_DROP; > + > + /* If offset=0, port range is in one contiguous block */ > + if (base) > + off = prandom_u32_max(((1 << 16) / base) - 1); Assuming the example above, base is set to 1024. Then, off is a random value between UINT16_MAX (you expressed this as 1 << 16) and the base which is 1024 minus 1. So this is picking a random off (actually the PSID?) between 0 and 63. What about clashes? I mean, two different machines behind the NAT might get the same off. > + newrange.min_proto.all = htons(min + base * off); min could be 1024, 2048, 3072... you add base which is 1024 * off. Is this duplicated? Both calculated in user and kernel space? > + newrange.max_proto.all = htons(ntohs(newrange.min_proto.all) + ntohs(range->max_proto.all) - min); I'm stopping here, I'm getting lost. My understanding about this RFC is that you would like to split the 16-bit ports in ranges to uniquely identify the host behind the NAT. Why don't you just you just select the port range from userspace utilizing the existing infrastructure? I mean, why do you need this kernel patch? Florian already suggested: > Is it really needed to place all of this in the nat core? > > The only thing that has to be done in the NAT core, afaics, is to > suppress port reallocation attmepts when NF_NAT_RANGE_PSID is set. > > Is there a reason why nf_nat_masquerade_ipv4/6 can't be changed instead > to do what you want? > > AFAICS its enough to set NF_NAT_RANGE_PROTO_SPECIFIED and init the > upper/lower boundaries, i.e. change input given to nf_nat_setup_info(). extracted from: https://patchwork.ozlabs.org/project/netfilter-devel/patch/20210422023506.4651-1-Cole.Dishington@xxxxxxxxxxxxxxxxxxx/
