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netfilter: nf_conntrack_ipv6: improve fragmentation handling

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The IPv6 conntrack fragmentation currently has a couple of shortcomings.
Fragmentes are collected in PREROUTING/OUTPUT, are defragmented, the
defragmented packet is then passed to conntrack, the resulting conntrack
information is attached to each original fragment and the fragments then
continue their way through the stack.

Helper invocation occurs in the POSTROUTING hook, at which point only
the original fragments are available. The result of this is that
fragmented packets are never passed to helpers.

This patch improves the situation in the following way:

- If a reassembled packet belongs to a connection that has a helper
  assigned, the reassembled packet is passed through the stack instead
  of the original fragments.

- During defragmentation, the largest received fragment size is stored.
  On output, the packet is refragmented if required. If the largest
  received fragment size exceeds the outgoing MTU, a "packet too big"
  message is generated, thus behaving as if the original fragments
  were passed through the stack from an outside point of view.

- The ipv6_helper() hook function can't receive fragments anymore for
  connections using a helper, so it is switched to use ipv6_skip_exthdr()
  instead of the netfilter specific nf_ct_ipv6_skip_exthdr() and the
  reassembled packets are passed to connection tracking helpers.

The result of this is that we can properly track fragmented packets, but
still generate ICMPv6 Packet too big messages if we would have before.

This patch is also required as a precondition for IPv6 NAT, where NAT
helpers might enlarge packets up to a point that they require
fragmentation. In that case we can't generate Packet too big messages
since the proper MTU can't be calculated in all cases (f.i. when
changing textual representation of a variable amount of addresses),
so the packet is transparently fragmented iff the original packet or
fragments would have fit the outgoing MTU.

IPVS parts by Jesper Dangaard Brouer <brouer@redhat.com>.

Change-Id: I75d83668e7de723fb271232f475f46f4037a4a4f
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>

Conflicts:
    net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
    net/ipv6/netfilter/nf_conntrack_reasm.c

Conflicts are due to the fact that Samsung backported
commit 6aafeef03b9d9ecf255f3a80ed85ee070260e1ae :
netfilter: push reasm skb through instead of original frag skbs
in latest source drop.
This commit is contained in:
Patrick McHardy
2019-08-09 09:14:08 +02:00
committed by Francescodario Cuzzocrea
parent c699801ee9
commit 82a0debf71
4 changed files with 45 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files
net/ipv6/ip6_output.c
+5 -2
View File
@@ -505,7 +505,8 @@ int ip6_forward(struct sk_buff *skb)
if (mtu < IPV6_MIN_MTU)
mtu = IPV6_MIN_MTU;
if (skb->len > mtu && !skb_is_gso(skb)) {
if ((!skb->local_df && skb->len > mtu && !skb_is_gso(skb)) ||
(IP6CB(skb)->frag_max_size && IP6CB(skb)->frag_max_size > mtu)) {
/* Again, force OUTPUT device used as source address */
skb->dev = dst->dev;
icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);
@@ -644,7 +645,9 @@ int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
/* We must not fragment if the socket is set to force MTU discovery
* or if the skb it not generated by a local socket.
*/
if (!skb->local_df && skb->len > mtu) {
if ((!skb->local_df && skb->len > mtu) ||
(IP6CB(skb)->frag_max_size &&
IP6CB(skb)->frag_max_size > mtu)) {
skb->dev = skb_dst(skb)->dev;
icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);
IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
+8 -7
View File
@@ -153,10 +153,10 @@ static unsigned int ipv6_helper(unsigned int hooknum,
const struct nf_conn_help *help;
const struct nf_conntrack_helper *helper;
enum ip_conntrack_info ctinfo;
unsigned int ret, protoff;
unsigned int extoff = (u8 *)(ipv6_hdr(skb) + 1) - skb->data;
unsigned char pnum = ipv6_hdr(skb)->nexthdr;
unsigned int ret;
__be16 frag_off;
int protoff;
u8 nexthdr;
/* This is where we call the helper: as the packet goes out. */
ct = nf_ct_get(skb, &ctinfo);
@@ -171,9 +171,10 @@ static unsigned int ipv6_helper(unsigned int hooknum,
if (!helper)
return NF_ACCEPT;
protoff = nf_ct_ipv6_skip_exthdr(skb, extoff, &pnum,
skb->len - extoff);
if (protoff > skb->len || pnum == NEXTHDR_FRAGMENT) {
nexthdr = ipv6_hdr(skb)->nexthdr;
protoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr,
&frag_off);
if (protoff < 0 || (frag_off & htons(~0x7)) != 0) {
pr_debug("proto header not found\n");
return NF_ACCEPT;
}
net/ipv6/netfilter/nf_conntrack_reasm.c
+8 -1
View File
@@ -191,6 +191,7 @@ static int nf_ct_frag6_queue(struct nf_ct_frag6_queue *fq, struct sk_buff *skb,
const struct frag_hdr *fhdr, int nhoff)
{
struct sk_buff *prev, *next;
unsigned int payload_len;
int offset, end;
if (fq->q.last_in & INET_FRAG_COMPLETE) {
@@ -198,8 +199,10 @@ static int nf_ct_frag6_queue(struct nf_ct_frag6_queue *fq, struct sk_buff *skb,
goto err;
}
payload_len = ntohs(ipv6_hdr(skb)->payload_len);
offset = ntohs(fhdr->frag_off) & ~0x7;
end = offset + (ntohs(ipv6_hdr(skb)->payload_len) -
end = offset + (payload_len -
((u8 *)(fhdr + 1) - (u8 *)(ipv6_hdr(skb) + 1)));
if ((unsigned int)end > IPV6_MAXPLEN) {
@@ -308,6 +311,8 @@ found:
skb->dev = NULL;
fq->q.stamp = skb->tstamp;
fq->q.meat += skb->len;
if (payload_len > fq->q.max_size)
fq->q.max_size = payload_len;
atomic_add(skb->truesize, &nf_init_frags.mem);
/* The first fragment.
@@ -413,10 +418,12 @@ nf_ct_frag6_reasm(struct nf_ct_frag6_queue *fq, struct net_device *dev)
}
atomic_sub(head->truesize, &nf_init_frags.mem);
head->local_df = 1;
head->next = NULL;
head->dev = dev;
head->tstamp = fq->q.stamp;
ipv6_hdr(head)->payload_len = htons(payload_len);
IP6CB(head)->frag_max_size = sizeof(struct ipv6hdr) + fq->q.max_size;
/* Yes, and fold redundant checksum back. 8) */
if (head->ip_summed == CHECKSUM_COMPLETE)
net/netfilter/ipvs/ip_vs_xmit.c
+24 -3
View File
@@ -462,7 +462,14 @@ ip_vs_bypass_xmit_v6(struct sk_buff *skb, struct ip_vs_conn *cp,
/* MTU checking */
mtu = dst_mtu(&rt->dst);
if (skb->len > mtu && !skb_is_gso(skb)) {
if (IP6CB(skb)->frag_max_size) {
/* frag_max_size tell us that, this packet have been
* defragmented by netfilter IPv6 conntrack module.
*/
if (IP6CB(skb)->frag_max_size > mtu)
return true; /* largest fragment violate MTU */
}
else if (skb->len > mtu && !skb_is_gso(skb)) {
if (!skb->dev) {
struct net *net = dev_net(skb_dst(skb)->dev);
@@ -683,7 +690,14 @@ ip_vs_nat_xmit_v6(struct sk_buff *skb, struct ip_vs_conn *cp,
/* MTU checking */
mtu = dst_mtu(&rt->dst);
if (skb->len > mtu && !skb_is_gso(skb)) {
if (IP6CB(skb)->frag_max_size) {
/* frag_max_size tell us that, this packet have been
* defragmented by netfilter IPv6 conntrack module.
*/
if (IP6CB(skb)->frag_max_size > mtu)
return true; /* largest fragment violate MTU */
}
else if (skb->len > mtu && !skb_is_gso(skb)) {
if (!skb->dev) {
struct net *net = dev_net(skb_dst(skb)->dev);
@@ -1318,7 +1332,14 @@ ip_vs_icmp_xmit_v6(struct sk_buff *skb, struct ip_vs_conn *cp,
/* MTU checking */
mtu = dst_mtu(&rt->dst);
if (skb->len > mtu && !skb_is_gso(skb)) {
if (IP6CB(skb)->frag_max_size) {
/* frag_max_size tell us that, this packet have been
* defragmented by netfilter IPv6 conntrack module.
*/
if (IP6CB(skb)->frag_max_size > mtu)
return true; /* largest fragment violate MTU */
}
else if (skb->len > mtu && !skb_is_gso(skb)) {
if (!skb->dev) {
struct net *net = dev_net(skb_dst(skb)->dev);