netfilter: nf_tables: prepare set element accounting for async updates

Use atomic operations for the element count to avoid races with async
updates.

To properly handle the transactional semantics during netlink updates,
deleted but not yet committed elements are accounted for seperately and
are treated as being already removed. This means for the duration of
a netlink transaction, the limit might be exceeded by the amount of
elements deleted. Set implementations must be prepared to handle this.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

2 files changed, 14 insertions, 10 deletions

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index 0dab872e821b..27d1bf55a581 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -3238,9 +3238,6 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
         u32 flags;
         int err;
 
-        if (set->size && set->nelems == set->size)
-                return -ENFILE;
-
         err = nla_parse_nested(nla, NFTA_SET_ELEM_MAX, attr,
                                nft_set_elem_policy);
         if (err < 0)
@@ -3391,11 +3388,15 @@ static int nf_tables_newsetelem(struct sock *nlsk, struct sk_buff *skb,
                 return -EBUSY;
 
         nla_for_each_nested(attr, nla[NFTA_SET_ELEM_LIST_ELEMENTS], rem) {
+                if (set->size &&
+                    !atomic_add_unless(&set->nelems, 1, set->size + set->ndeact))
+                        return -ENFILE;
+
                 err = nft_add_set_elem(&ctx, set, attr);
-                if (err < 0)
+                if (err < 0) {
+                        atomic_dec(&set->nelems);
                         break;
-
-                set->nelems++;
+                }
         }
         return err;
 }
@@ -3477,7 +3478,7 @@ static int nf_tables_delsetelem(struct sock *nlsk, struct sk_buff *skb,
                 if (err < 0)
                         break;
 
-                set->nelems--;
+                set->ndeact++;
         }
         return err;
 }
@@ -3810,6 +3811,8 @@ static int nf_tables_commit(struct sk_buff *skb)
                                                  &te->elem,
                                                  NFT_MSG_DELSETELEM, 0);
                         te->set->ops->remove(te->set, &te->elem);
+                        atomic_dec(&te->set->nelems);
+                        te->set->ndeact--;
                         break;
                 }
         }
@@ -3913,16 +3916,16 @@ static int nf_tables_abort(struct sk_buff *skb)
                         nft_trans_destroy(trans);
                         break;
                 case NFT_MSG_NEWSETELEM:
-                        nft_trans_elem_set(trans)->nelems--;
                         te = (struct nft_trans_elem *)trans->data;
 
                         te->set->ops->remove(te->set, &te->elem);
+                        atomic_dec(&te->set->nelems);
                         break;
                 case NFT_MSG_DELSETELEM:
                         te = (struct nft_trans_elem *)trans->data;
 
-                        nft_trans_elem_set(trans)->nelems++;
                         te->set->ops->activate(te->set, &te->elem);
+                        te->set->ndeact--;
 
                         nft_trans_destroy(trans);
                         break;
diff --git a/net/netfilter/nft_hash.c b/net/netfilter/nft_hash.c
index 5923ec547268..c74e2bf1a1e4 100644
--- a/net/netfilter/nft_hash.c
+++ b/net/netfilter/nft_hash.c
@@ -203,7 +203,7 @@ out:
 
 static void nft_hash_gc(struct work_struct *work)
 {
-        const struct nft_set *set;
+        struct nft_set *set;
         struct nft_hash_elem *he;
         struct nft_hash *priv;
         struct nft_set_gc_batch *gcb = NULL;
@@ -237,6 +237,7 @@ static void nft_hash_gc(struct work_struct *work)
                 if (gcb == NULL)
                         goto out;
                 rhashtable_remove_fast(&priv->ht, &he->node, nft_hash_params);
+                atomic_dec(&set->nelems);
                 nft_set_gc_batch_add(gcb, he);
         }
 out: