On Thu, Aug 09, 2012 at 10:08:49PM +0200, kaber@xxxxxxxxx wrote: > From: Patrick McHardy <kaber@xxxxxxxxx> > > 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. > > Signed-off-by: Patrick McHardy <kaber@xxxxxxxxx> > --- > include/linux/ipv6.h | 1 + > net/ipv6/ip6_output.c | 7 +++- > net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c | 37 ++++++++++++++++++------ > net/ipv6/netfilter/nf_conntrack_reasm.c | 19 ++++++++++-- > 4 files changed, 50 insertions(+), 14 deletions(-) > > diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h > index 879db26..0b94e91 100644 > --- a/include/linux/ipv6.h > +++ b/include/linux/ipv6.h > @@ -256,6 +256,7 @@ struct inet6_skb_parm { > #if defined(CONFIG_IPV6_MIP6) || defined(CONFIG_IPV6_MIP6_MODULE) > __u16 dsthao; > #endif > + __u16 frag_max_size; > > #define IP6SKB_XFRM_TRANSFORMED 1 > #define IP6SKB_FORWARDED 2 > diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c > index 5b2d63e..a4f6263 100644 > --- a/net/ipv6/ip6_output.c > +++ b/net/ipv6/ip6_output.c > @@ -493,7 +493,8 @@ 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); > @@ -636,7 +637,9 @@ 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 (unlikely(!skb->local_df && skb->len > mtu)) { > + if (unlikely(!skb->local_df && skb->len > mtu) || > + (IP6CB(skb)->frag_max_size && > + IP6CB(skb)->frag_max_size > mtu)) { > if (skb->sk && dst_allfrag(skb_dst(skb))) > sk_nocaps_add(skb->sk, NETIF_F_GSO_MASK); > > diff --git a/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c b/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c > index 4794f96..560d823 100644 > --- a/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c > +++ b/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c > @@ -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 & ntohs(~0x7)) != 0) { > pr_debug("proto header not found\n"); > return NF_ACCEPT; > } > @@ -199,9 +200,13 @@ static unsigned int ipv6_confirm(unsigned int hooknum, > static unsigned int __ipv6_conntrack_in(struct net *net, > unsigned int hooknum, > struct sk_buff *skb, > + const struct net_device *in, > + const struct net_device *out, > int (*okfn)(struct sk_buff *)) > { > struct sk_buff *reasm = skb->nfct_reasm; > + struct nf_conn *ct; > + enum ip_conntrack_info ctinfo; > > /* This packet is fragmented and has reassembled packet. */ > if (reasm) { > @@ -213,6 +218,20 @@ static unsigned int __ipv6_conntrack_in(struct net *net, > if (ret != NF_ACCEPT) > return ret; > } > + > + /* Conntrack helpers need the entire reassembled packet in the > + * POST_ROUTING hook. > + */ > + ct = nf_ct_get(reasm, &ctinfo); > + if (ct != NULL && test_bit(IPS_HELPER_BIT, &ct->status)) { Two things regarding the line above: - I think this also need to check for !nf_ct_is_untracked(ct) - IPS_HELPER_BIT is only set if the CT target is used to attach helpers. I know, this behaviour may seem confusing, but I didn't find any better way to avoid that NAT removes the helper explicitly attached via CT. So basically now that status bit means: "this helper has been attached via CT". Setting it inconditionally in __nf_ct_try_assign_helper would break the magic auto-assign helper code. On the other hand, the automatic helper assignment is scheduled to be removed (well, it would still take at least one 1.5/2 years before we do so). At that time, we'll be able to say that all conntrack with IPS_HELPER really has one helper. But now I think that you'll have to use for nfct_help instead to check if that ct has a helper. > + nf_conntrack_get_reasm(skb); > + NF_HOOK_THRESH(NFPROTO_IPV6, hooknum, reasm, > + (struct net_device *)in, > + (struct net_device *)out, > + okfn, NF_IP6_PRI_CONNTRACK + 1); > + return NF_DROP_ERR(-ECANCELED); > + } > + > nf_conntrack_get(reasm->nfct); > skb->nfct = reasm->nfct; > skb->nfctinfo = reasm->nfctinfo; > @@ -228,7 +247,7 @@ static unsigned int ipv6_conntrack_in(unsigned int hooknum, > const struct net_device *out, > int (*okfn)(struct sk_buff *)) > { > - return __ipv6_conntrack_in(dev_net(in), hooknum, skb, okfn); > + return __ipv6_conntrack_in(dev_net(in), hooknum, skb, in, out, okfn); > } > > static unsigned int ipv6_conntrack_local(unsigned int hooknum, > @@ -242,7 +261,7 @@ static unsigned int ipv6_conntrack_local(unsigned int hooknum, > net_notice_ratelimited("ipv6_conntrack_local: packet too short\n"); > return NF_ACCEPT; > } > - return __ipv6_conntrack_in(dev_net(out), hooknum, skb, okfn); > + return __ipv6_conntrack_in(dev_net(out), hooknum, skb, in, out, okfn); > } > > static struct nf_hook_ops ipv6_conntrack_ops[] __read_mostly = { > diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c > index c9c78c2..f94fb3a 100644 > --- a/net/ipv6/netfilter/nf_conntrack_reasm.c > +++ b/net/ipv6/netfilter/nf_conntrack_reasm.c > @@ -190,6 +190,7 @@ 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) { > @@ -197,8 +198,10 @@ 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) { > @@ -307,6 +310,8 @@ 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. > @@ -412,10 +417,12 @@ 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) > @@ -592,6 +599,7 @@ void nf_ct_frag6_output(unsigned int hooknum, struct sk_buff *skb, > int (*okfn)(struct sk_buff *)) > { > struct sk_buff *s, *s2; > + unsigned int ret = 0; > > for (s = NFCT_FRAG6_CB(skb)->orig; s;) { > nf_conntrack_put_reasm(s->nfct_reasm); > @@ -601,8 +609,13 @@ void nf_ct_frag6_output(unsigned int hooknum, struct sk_buff *skb, > s2 = s->next; > s->next = NULL; > > - NF_HOOK_THRESH(NFPROTO_IPV6, hooknum, s, in, out, okfn, > - NF_IP6_PRI_CONNTRACK_DEFRAG + 1); > + if (ret != -ECANCELED) > + ret = NF_HOOK_THRESH(NFPROTO_IPV6, hooknum, s, > + in, out, okfn, > + NF_IP6_PRI_CONNTRACK_DEFRAG + 1); > + else > + kfree_skb(s); > + > s = s2; > } > nf_conntrack_put_reasm(skb); > -- > 1.7.1 > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html