netfilter: nf_conntrack: per netns nf_conntrack_cachep

nf_conntrack_cachep is currently shared by all netns instances, but
because of SLAB_DESTROY_BY_RCU special semantics, this is wrong.

If we use a shared slab cache, one object can instantly flight between
one hash table (netns ONE) to another one (netns TWO), and concurrent
reader (doing a lookup in netns ONE, 'finding' an object of netns TWO)
can be fooled without notice, because no RCU grace period has to be
observed between object freeing and its reuse.

We dont have this problem with UDP/TCP slab caches because TCP/UDP
hashtables are global to the machine (and each object has a pointer to
its netns).

If we use per netns conntrack hash tables, we also *must* use per netns
conntrack slab caches, to guarantee an object can not escape from one
namespace to another one.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
[Patrick: added unique slab name allocation]
Cc: stable@kernel.org
Signed-off-by: Patrick McHardy <kaber@trash.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/net/netns/conntrack.h b/include/net/netns/conntrack.h
index ba1ba0c5efd1..aed23b6c8478 100644
--- a/include/net/netns/conntrack.h
+++ b/include/net/netns/conntrack.h
@@ -11,6 +11,7 @@ struct nf_conntrack_ecache;
 struct netns_ct {
         atomic_t                count;
         unsigned int            expect_count;
+        struct kmem_cache       *nf_conntrack_cachep;
         struct hlist_nulls_head *hash;
         struct hlist_head       *expect_hash;
         struct hlist_nulls_head unconfirmed;
@@ -28,5 +29,6 @@ struct netns_ct {
 #endif
         int                     hash_vmalloc;
         int                     expect_vmalloc;
+        char                    *slabname;
 };
 #endif