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Subject[PATCH] net: netfilter: Add RFC-7597 Section 5.1 PSID support
Date
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@alliedtelesis.co.nz>
Signed-off-by: Anthony Lineham <anthony.lineham@alliedtelesis.co.nz>
Co-developed-by: Scott Parlane <scott.parlane@alliedtelesis.co.nz>
Signed-off-by: Scott Parlane <scott.parlane@alliedtelesis.co.nz>
Signed-off-by: Blair Steven <blair.steven@alliedtelesis.co.nz>
Signed-off-by: Cole Dishington <Cole.Dishington@alliedtelesis.co.nz>
---

Notes:
Changes in v3:
- Select pseudo random port range (for a given psid) to search in
nf_nat_l4proto_unique_tuple(), rather than exhausive search of all
port ranges (for a given psid).
- Remove extra check in get_unique_tuple for psid, it is not needed
if NF_NAT_RANGE_PROTO_SPECIFIED is set.

net/netfilter/nf_nat_core.c | 33 +++++++++++++++++++++++++++----
net/netfilter/nf_nat_masquerade.c | 17 ++++++++++++++--
2 files changed, 44 insertions(+), 6 deletions(-)

diff --git a/net/netfilter/nf_nat_core.c b/net/netfilter/nf_nat_core.c
index 7de595ead06a..1fbf98cade41 100644
--- a/net/netfilter/nf_nat_core.c
+++ b/net/netfilter/nf_nat_core.c
@@ -195,13 +195,30 @@ static bool nf_nat_inet_in_range(const struct nf_conntrack_tuple *t,
static bool l4proto_in_range(const struct nf_conntrack_tuple *tuple,
enum nf_nat_manip_type maniptype,
const union nf_conntrack_man_proto *min,
- const union nf_conntrack_man_proto *max)
+ const union nf_conntrack_man_proto *max,
+ const union nf_conntrack_man_proto *base,
+ bool is_psid)
{
__be16 port;
+ u16 psid, psid_mask, offset_mask;
+
+ /* In this case we are in PSID mode, avoid checking all ranges by computing bitmasks */
+ if (is_psid) {
+ u16 j = ntohs(max->all) - ntohs(min->all) + 1;
+ u16 a = (1 << 16) / ntohs(base->all);
+
+ offset_mask = (a - 1) * ntohs(base->all);
+ psid_mask = ((ntohs(base->all) / j) << 1) - 1;
+ psid = ntohs(min->all) & psid_mask;
+ }

switch (tuple->dst.protonum) {
case IPPROTO_ICMP:
case IPPROTO_ICMPV6:
+ if (is_psid) {
+ return ((ntohs(tuple->src.u.icmp.id) & offset_mask) != 0) &&
+ ((ntohs(tuple->src.u.icmp.id) & psid_mask) == psid);
+ }
return ntohs(tuple->src.u.icmp.id) >= ntohs(min->icmp.id) &&
ntohs(tuple->src.u.icmp.id) <= ntohs(max->icmp.id);
case IPPROTO_GRE: /* all fall though */
@@ -215,6 +232,10 @@ static bool l4proto_in_range(const struct nf_conntrack_tuple *tuple,
else
port = tuple->dst.u.all;

+ if (is_psid) {
+ return ((ntohs(port) & offset_mask) != 0) &&
+ ((ntohs(port) & psid_mask) == psid);
+ }
return ntohs(port) >= ntohs(min->all) &&
ntohs(port) <= ntohs(max->all);
default:
@@ -239,7 +260,8 @@ static int in_range(const struct nf_conntrack_tuple *tuple,
return 1;

return l4proto_in_range(tuple, NF_NAT_MANIP_SRC,
- &range->min_proto, &range->max_proto);
+ &range->min_proto, &range->max_proto, &range->base_proto,
+ range->flags & NF_NAT_RANGE_PSID);
}

static inline int
@@ -532,8 +554,11 @@ get_unique_tuple(struct nf_conntrack_tuple *tuple,
if (range->flags & NF_NAT_RANGE_PROTO_SPECIFIED) {
if (!(range->flags & NF_NAT_RANGE_PROTO_OFFSET) &&
l4proto_in_range(tuple, maniptype,
- &range->min_proto,
- &range->max_proto) &&
+ &range->min_proto,
+ &range->max_proto,
+ &range->base_proto,
+ range->flags &
+ NF_NAT_RANGE_PSID) &&
(range->min_proto.all == range->max_proto.all ||
!nf_nat_used_tuple(tuple, ct)))
return;
diff --git a/net/netfilter/nf_nat_masquerade.c b/net/netfilter/nf_nat_masquerade.c
index 8e8a65d46345..423b3774e65c 100644
--- a/net/netfilter/nf_nat_masquerade.c
+++ b/net/netfilter/nf_nat_masquerade.c
@@ -55,8 +55,21 @@ 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 off = prandom_u32();
+ u16 base = ntohs(range->base_proto.all);
+ u16 min = ntohs(range->min_proto.all);
+ u16 max_off = ((1 << 16) / base) - 1;
+
+ newrange.flags = newrange.flags | NF_NAT_RANGE_PROTO_SPECIFIED;
+ newrange.min_proto.all = htons(min + base * (off % max_off));
+ newrange.max_proto.all = htons(ntohs(newrange.min_proto.all) + ntohs(range->max_proto.all) - min);
+ newrange.base_proto = range->base_proto;
+ } else {
+ newrange.min_proto = range->min_proto;
+ newrange.max_proto = range->max_proto;
+ }

/* Hand modified range to generic setup. */
return nf_nat_setup_info(ct, &newrange, NF_NAT_MANIP_SRC);
--
2.32.0
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