[NETFILTER]: nf_conntrack_expect: introduce nf_conntrack_expect_max sysct

As a last step of preventing DoS by creating lots of expectations, this
patch introduces a global maximum and a sysctl to control it. The default
is initialized to 4 * the expectation hash table size, which results in
1/64 of the default maxmimum of conntracks.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 19 insertions, 1 deletions

diff --git a/include/net/netfilter/nf_conntrack_expect.h b/include/net/netfilter/nf_conntrack_expect.h
index 9d5af4e22c4f..cae1a0dce365 100644
--- a/include/net/netfilter/nf_conntrack_expect.h
+++ b/include/net/netfilter/nf_conntrack_expect.h
@@ -8,6 +8,7 @@
 
 extern struct hlist_head *nf_ct_expect_hash;
 extern unsigned int nf_ct_expect_hsize;
+extern unsigned int nf_ct_expect_max;
 
 struct nf_conntrack_expect
 {
diff --git a/net/netfilter/nf_conntrack_expect.c b/net/netfilter/nf_conntrack_expect.c
index 5ef0dd439e76..513828fdaa2c 100644
--- a/net/netfilter/nf_conntrack_expect.c
+++ b/net/netfilter/nf_conntrack_expect.c
@@ -35,6 +35,7 @@ EXPORT_SYMBOL_GPL(nf_ct_expect_hsize);
 
 static unsigned int nf_ct_expect_hash_rnd __read_mostly;
 static unsigned int nf_ct_expect_count;
+unsigned int nf_ct_expect_max __read_mostly;
 static int nf_ct_expect_hash_rnd_initted __read_mostly;
 static int nf_ct_expect_vmalloc;
 
@@ -367,6 +368,14 @@ int nf_ct_expect_related(struct nf_conntrack_expect *expect)
             master_help->expecting >= master_help->helper->max_expected)
                 evict_oldest_expect(master);
 
+        if (nf_ct_expect_count >= nf_ct_expect_max) {
+                if (net_ratelimit())
+                        printk(KERN_WARNING
+                               "nf_conntrack: expectation table full");
+                ret = -EMFILE;
+                goto out;
+        }
+
         nf_ct_expect_insert(expect);
         nf_ct_expect_event(IPEXP_NEW, expect);
         ret = 0;
@@ -522,6 +531,7 @@ int __init nf_conntrack_expect_init(void)
                 if (!nf_ct_expect_hsize)
                         nf_ct_expect_hsize = 1;
         }
+        nf_ct_expect_max = nf_ct_expect_hsize * 4;
 
         nf_ct_expect_hash = nf_ct_alloc_hashtable(&nf_ct_expect_hsize,
                                                   &nf_ct_expect_vmalloc);
diff --git a/net/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
index 098e7993932a..6af96c6e29fb 100644
--- a/net/netfilter/nf_conntrack_standalone.c
+++ b/net/netfilter/nf_conntrack_standalone.c
@@ -372,7 +372,14 @@ static ctl_table nf_ct_sysctl_table[] = {
                 .extra1         = &log_invalid_proto_min,
                 .extra2         = &log_invalid_proto_max,
         },
-
+        {
+                .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "nf_conntrack_expect_max",
+                .data           = &nf_ct_expect_max,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec,
+        },
         { .ctl_name = 0 }
 };