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Message-ID: <20130313012715.GE14801@order.stressinduktion.org>
Date: Wed, 13 Mar 2013 02:27:15 +0100
From: Hannes Frederic Sowa <hannes@...essinduktion.org>
To: Eric Dumazet <eric.dumazet@...il.com>
Cc: netdev@...r.kernel.org, yoshfuji@...ux-ipv6.org, brouer@...hat.com
Subject: Re: [PATCH RFC] ipv6: use stronger hash for reassembly queue hash table
[cc'ing Jesper, too]
On Fri, Mar 08, 2013 at 07:23:39AM -0800, Eric Dumazet wrote:
> On Fri, 2013-03-08 at 16:08 +0100, Hannes Frederic Sowa wrote:
> > On Fri, Mar 08, 2013 at 06:53:06AM -0800, Eric Dumazet wrote:
> > > No matter how you hash, a hacker can easily fill your defrag unit with
> > > not complete datagrams, so what's the point ?
> >
> > I want to harden reassembly logic against all fragments being put in
> > the same hash bucket because of malicious traffic and thus creating
> > long list traversals in the fragment queue hash table.
>
> Note that the long traversal was a real issue with TCP (thats why I
> introduced ipv6_addr_jhash()), as a single ehash slot could contains
> thousand of sockets.
>
> But with fragments, we should just limit the depth of any particular
> slot, and drop above a particular threshold.
[PATCH net-next RFC] inet: add max_depth to limit list length in inet_frags hash
This does implement trivial drop for fragments where the hash queue
is above some limit.
I calculate the limit as follow:
I averaged the folowing formula
max_depth = max_threshold / INETFRAGS_HASHSZ / rounded up (SKB_TRUELEN(0)
sizeof(struct ipq or struct frag_queue))
to
max_threshold >> 15
So we start with a maximum list length of 128. I think we could halve
this value to 64, but because I have no real performance data I left it
at this higher value for now.
This patch does only protect IPv6 (and not netfilter ipv6 defragmentation)
and will switch off limit checking if max_depth is zero. I'll rewrite
the check if we agree that this simple solution is the way to go (simple
drop) and will clamp the minimum value to 1 as soon as I also migrated
ipv4 and netfilter to the new sysctl handler.
When testing this patch:
Disable netfilter defragmenation for ipv6 on your machine if you test
this patch, otherwise you won't see the improvment. Machine now runs
smoothly under fragmentation dos.
Ok if I target this patch for net next time because the hashing changes
are in there already?
Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
---
include/net/inet_frag.h | 13 +++++++++++++
net/ipv4/inet_fragment.c | 25 ++++++++++++++++++++++++-
net/ipv6/reassembly.c | 6 +++++-
3 files changed, 42 insertions(+), 2 deletions(-)
diff --git a/include/net/inet_frag.h b/include/net/inet_frag.h
index 76c3fe5..9ba6ada 100644
--- a/include/net/inet_frag.h
+++ b/include/net/inet_frag.h
@@ -17,6 +17,7 @@ struct netns_frags {
int timeout;
int high_thresh;
int low_thresh;
+ int max_depth;
};
struct inet_frag_queue {
@@ -43,6 +44,11 @@ struct inet_frag_queue {
#define INETFRAGS_HASHSZ 64
+/* max_depth = max_threshold / INETFRAGS_HASHSZ / rounded up (SKB_TRUELEN(0) +
+ * sizeof(struct ipq or struct frag_queue))
+ */
+#define INETFRAGS_MAXDEPTH_SHIFT 15
+
struct inet_frags {
struct hlist_head hash[INETFRAGS_HASHSZ];
/* This rwlock is a global lock (seperate per IPv4, IPv6 and
@@ -144,4 +150,11 @@ static inline void inet_frag_lru_add(struct netns_frags *nf,
list_add_tail(&q->lru_list, &nf->lru_list);
spin_unlock(&nf->lru_lock);
}
+
+#ifdef CONFIG_SYSCTL
+int inet_frag_update_high_thresh(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp,
+ loff_t *ppos);
+#endif
+
#endif
diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
index 245ae07..92f1fdd 100644
--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -277,6 +277,7 @@ struct inet_frag_queue *inet_frag_find(struct netns_frags *nf,
__releases(&f->lock)
{
struct inet_frag_queue *q;
+ int depth = 0;
hlist_for_each_entry(q, &f->hash[hash], list) {
if (q->net == nf && f->match(q, key)) {
@@ -284,9 +285,31 @@ struct inet_frag_queue *inet_frag_find(struct netns_frags *nf,
read_unlock(&f->lock);
return q;
}
+ depth++;
}
read_unlock(&f->lock);
- return inet_frag_create(nf, f, key);
+ if (!nf->max_depth || depth <= nf->max_depth)
+ return inet_frag_create(nf, f, key);
+ else
+ return NULL;
}
EXPORT_SYMBOL(inet_frag_find);
+
+#ifdef CONFIG_SYSCTL
+int inet_frag_update_high_thresh(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp,
+ loff_t *ppos)
+{
+ int ret;
+ ret = proc_dointvec(table, write, buffer, lenp, ppos);
+
+ if (!ret && write && table->extra1) {
+ int *data = table->data;
+ int *max_depth = table->extra1;
+ *max_depth = *data >> INETFRAGS_MAXDEPTH_SHIFT;
+ }
+ return ret;
+}
+EXPORT_SYMBOL(inet_frag_update_high_thresh);
+#endif
diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index 3c6a772..84b35f6 100644
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -558,7 +558,8 @@ static struct ctl_table ip6_frags_ns_ctl_table[] = {
.data = &init_net.ipv6.frags.high_thresh,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = proc_dointvec
+ .proc_handler = inet_frag_update_high_thresh,
+ .extra1 = &init_net.ipv6.frags.max_depth
},
{
.procname = "ip6frag_low_thresh",
@@ -600,6 +601,7 @@ static int __net_init ip6_frags_ns_sysctl_register(struct net *net)
goto err_alloc;
table[0].data = &net->ipv6.frags.high_thresh;
+ table[0].extra1 = &net->ipv6.frags.max_depth;
table[1].data = &net->ipv6.frags.low_thresh;
table[2].data = &net->ipv6.frags.timeout;
@@ -670,6 +672,8 @@ static int __net_init ipv6_frags_init_net(struct net *net)
net->ipv6.frags.high_thresh = IPV6_FRAG_HIGH_THRESH;
net->ipv6.frags.low_thresh = IPV6_FRAG_LOW_THRESH;
net->ipv6.frags.timeout = IPV6_FRAG_TIMEOUT;
+ net->ipv6.frags.max_depth =
+ IPV6_FRAG_HIGH_THRESH >> INETFRAGS_MAXDEPTH_SHIFT;
inet_frags_init_net(&net->ipv6.frags);
--
1.8.1.4
--
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