Re: DDoS attack causing bad effect on conntrack searches

Jesper Dangaard Brouer
2010-04-22T13:38:53Z

I have added a stats counter to prove my case, which I think we should add to the kernel (to detect the case in the future).
The DDoS attack has disappeared, so I guess I'll try to see if I can reproduce the problem in my testlab.

[PATCH] net: netfilter conntrack extended with extra stat counter.

From: Jesper Dangaard Brouer <hawk@comx.dk>

I suspect an unfortunatly series of events occuring under a DDoS
attack, in function __nf_conntrack_find() nf_contrack_core.c.

Adding a stats counter to see if the search is restarted too often.

Signed-off-by: Jesper Dangaard Brouer <hawk@comx.dk>
---

include/linux/netfilter/nf_conntrack_common.h | 1 +
.../netfilter/nf_conntrack_l3proto_ipv4_compat.c | 7 ++++---
net/netfilter/nf_conntrack_core.c | 4 +++-
net/netfilter/nf_conntrack_standalone.c | 7 ++++---
4 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/include/linux/netfilter/nf_conntrack_common.h b/include/linux/netfilter/nf_conntrack_common.h
index a8248ee..57ff312 100644
--- a/include/linux/netfilter/nf_conntrack_common.h
+++ b/include/linux/netfilter/nf_conntrack_common.h
@@ -93,6 +93,7 @@ struct ip_conntrack_stat
unsigned int expect_new;
unsigned int expect_create;
unsigned int expect_delete;
+ unsigned int search_restart;
};

/* call to create an explicit dependency on nf_conntrack. */
diff --git a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4_compat.c b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4_compat.c
index 8668a3d..b94f510 100644
--- a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4_compat.c
+++ b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4_compat.c
@@ -336,12 +336,12 @@ static int ct_cpu_seq_show(struct seq_file *seq, void *v)
const struct ip_conntrack_stat *st = v;

if (v == SEQ_START_TOKEN) {
- seq_printf(seq, "entries searched found new invalid ignore delete delete_list insert insert_failed drop early_drop icmp_error expect_new expect_create expect_delete\n");
+ seq_printf(seq, "entries searched found new invalid ignore delete delete_list insert insert_failed drop early_drop icmp_error expect_new expect_create expect_delete search_restart\n");
return 0;
}

seq_printf(seq, "%08x %08x %08x %08x %08x %08x %08x %08x "
- "%08x %08x %08x %08x %08x %08x %08x %08x \n",
+ "%08x %08x %08x %08x %08x %08x %08x %08x %08x\n",
nr_conntracks,
st->searched,
st->found,
@@ -358,7 +358,8 @@ static int ct_cpu_seq_show(struct seq_file *seq, void *v)

st->expect_new,
st->expect_create,
- st->expect_delete
+ st->expect_delete,
+ st->search_restart
);
return 0;
}
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 4299db7..5ca8286 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -315,8 +315,10 @@ begin:
* not the expected one, we must restart lookup.
* We probably met an item that was moved to another chain.
*/
- if (get_nulls_value(n) != hash)
+ if (get_nulls_value(n) != hash) {
+ NF_CT_STAT_INC(net, search_restart);
goto begin;
+ }
local_bh_enable();

return NULL;
diff --git a/net/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
index 1935153..4812750 100644
--- a/net/netfilter/nf_conntrack_standalone.c
+++ b/net/netfilter/nf_conntrack_standalone.c
@@ -245,12 +245,12 @@ static int ct_cpu_seq_show(struct seq_file *seq, void *v)
const struct ip_conntrack_stat *st = v;

if (v == SEQ_START_TOKEN) {
- seq_printf(seq, "entries searched found new invalid ignore delete delete_list insert insert_failed drop early_drop icmp_error expect_new expect_create expect_delete\n");
+ seq_printf(seq, "entries searched found new invalid ignore delete delete_list insert insert_failed drop early_drop icmp_error expect_new expect_create expect_delete search_restart\n");
return 0;
}

seq_printf(seq, "%08x %08x %08x %08x %08x %08x %08x %08x "
- "%08x %08x %08x %08x %08x %08x %08x %08x \n",
+ "%08x %08x %08x %08x %08x %08x %08x %08x %08x\n",
nr_conntracks,
st->searched,
st->found,
@@ -267,7 +267,8 @@ static int ct_cpu_seq_show(struct seq_file *seq, void *v)

st->expect_new,
st->expect_create,
- st->expect_delete
+ st->expect_delete,
+ st->search_restart
);
return 0;
}

--
Med venlig hilsen / Best regards
Jesper Brouer
ComX Networks A/S
Linux Network Kernel Developer
Cand. Scient Datalog / MSc.CS
Author of http://adsl-optimizer.dk
LinkedIn: http://www.linkedin.com/in/brouer