[PATCH nf-next v2] netfilter: nf_defrag_ipv4: Skip defrag if NOTRACK is set

[PATCH nf-next v2] netfilter: nf_defrag_ipv4: Skip defrag if NOTRACK is set

[Subash Abhinov Kasiviswanathan]

conntrack defrag is needed only if some module like CONNTRACK or NAT
explicitly requests it. For plain forwarding scenarios, defrag is
not needed and can be skipped if NOTRACK is set in a rule.

Since conntrack defrag is currently higher priority than raw table,
setting NOTRACK is not sufficient. We need to move raw to a higher
priority for iptables only.

This is achieved by introducing a module parameter which allows to
modify the priority. By default, the priority is NF_IP_PRI_RAW to
support legacy behavior.

v1->v2: Instead of modifying NF_IP_PRI_RAW itself, use a module
parameter to pass in the priority during module load as suggested
by Pablo. Also update commit text.

Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
---
 net/ipv4/netfilter/iptable_raw.c    | 14 +++++++++++++-
 net/ipv4/netfilter/nf_defrag_ipv4.c |  2 +-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/netfilter/iptable_raw.c b/net/ipv4/netfilter/iptable_raw.c
index 2642ecd..607392b 100644
--- a/net/ipv4/netfilter/iptable_raw.c
+++ b/net/ipv4/netfilter/iptable_raw.c
@@ -12,7 +12,11 @@
 
 static int __net_init iptable_raw_table_init(struct net *net);
 
-static const struct xt_table packet_raw = {
+static int priority __read_mostly = NF_IP_PRI_RAW;
+MODULE_PARM_DESC(priority, "Priority of IPv4 raw table (NF_IP_PRI_RAW)");
+module_param(priority, int, 0000);
+
+static struct xt_table packet_raw = {
 	.name = "raw",
 	.valid_hooks =  RAW_VALID_HOOKS,
 	.me = THIS_MODULE,
@@ -70,6 +74,14 @@ static int __init iptable_raw_init(void)
 {
 	int ret;
 
+	if (priority < NF_IP_PRI_CONNTRACK_DEFRAG &&
+	    priority > NF_IP_PRI_FIRST) {
+		packet_raw.priority = priority;
+
+		pr_info("iptable_raw: Using custom rule priority=%d\n",
+			packet_raw.priority);
+	}
+
 	rawtable_ops = xt_hook_ops_alloc(&packet_raw, iptable_raw_hook);
 	if (IS_ERR(rawtable_ops))
 		return PTR_ERR(rawtable_ops);
diff --git a/net/ipv4/netfilter/nf_defrag_ipv4.c b/net/ipv4/netfilter/nf_defrag_ipv4.c
index 37fe1616..cbd987f 100644
--- a/net/ipv4/netfilter/nf_defrag_ipv4.c
+++ b/net/ipv4/netfilter/nf_defrag_ipv4.c
@@ -80,7 +80,7 @@ static unsigned int ipv4_conntrack_defrag(void *priv,
 #endif
 #endif
 	/* Gather fragments. */
-	if (ip_is_fragment(ip_hdr(skb))) {
+	if (skb->_nfct != IP_CT_UNTRACKED && ip_is_fragment(ip_hdr(skb))) {
 		enum ip_defrag_users user =
 			nf_ct_defrag_user(state->hook, skb);
 
-- 
1.9.1

Re: [PATCH nf-next v2] netfilter: nf_defrag_ipv4: Skip defrag if NOTRACK is set

[Pablo Neira Ayuso]

Hi Subash,

On Tue, Dec 19, 2017 at 02:42:19PM -0700, Subash Abhinov Kasiviswanathan wrote:
> conntrack defrag is needed only if some module like CONNTRACK or NAT
> explicitly requests it. For plain forwarding scenarios, defrag is
> not needed and can be skipped if NOTRACK is set in a rule.
> 
> Since conntrack defrag is currently higher priority than raw table,
> setting NOTRACK is not sufficient. We need to move raw to a higher
> priority for iptables only.
> 
> This is achieved by introducing a module parameter which allows to
> modify the priority. By default, the priority is NF_IP_PRI_RAW to
> support legacy behavior.
> 
> v1->v2: Instead of modifying NF_IP_PRI_RAW itself, use a module
> parameter to pass in the priority during module load as suggested
> by Pablo. Also update commit text.

Can we get the same thing for IPv6, for symmetry?

Thanks!

Re: [PATCH nf-next v2] netfilter: nf_defrag_ipv4: Skip defrag if NOTRACK is set

[Subash Abhinov Kasiviswanathan]

> Can we get the same thing for IPv6, for symmetry?
> 
> Thanks!

Hi Pablo

Yes, I can include IPv6 in v3.

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