[PATCH 03/14] netfilter: nf_tables: fix race when create new element in dynset

[Pablo Neira Ayuso]

From: Liping Zhang <zlpnob...@gmail.com>

Packets may race when create the new element in nft_hash_update:
       CPU0                 CPU1
  lookup_fast - fail     lookup_fast - fail
       new - ok             new - ok
     insert - ok         insert - fail(EEXIST)

So when race happened, we reuse the existing element. Otherwise,
these *racing* packets will not be handled properly.

Fixes: 22fe54d5fefc ("netfilter: nf_tables: add support for dynamic set 
updates")
Signed-off-by: Liping Zhang <zlpnob...@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pa...@netfilter.org>
---
 net/netfilter/nft_set_hash.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nft_set_hash.c b/net/netfilter/nft_set_hash.c
index 88d9fc8343e7..a3dface3e6e6 100644
--- a/net/netfilter/nft_set_hash.c
+++ b/net/netfilter/nft_set_hash.c
@@ -98,7 +98,7 @@ static bool nft_hash_update(struct nft_set *set, const u32 
*key,
                            const struct nft_set_ext **ext)
 {
        struct nft_hash *priv = nft_set_priv(set);
-       struct nft_hash_elem *he;
+       struct nft_hash_elem *he, *prev;
        struct nft_hash_cmp_arg arg = {
                .genmask = NFT_GENMASK_ANY,
                .set     = set,
@@ -112,9 +112,18 @@ static bool nft_hash_update(struct nft_set *set, const u32 
*key,
        he = new(set, expr, regs);
        if (he == NULL)
                goto err1;
-       if (rhashtable_lookup_insert_key(&priv->ht, &arg, &he->node,
-                                        nft_hash_params))
+
+       prev = rhashtable_lookup_get_insert_key(&priv->ht, &arg, &he->node,
+                                               nft_hash_params);
+       if (IS_ERR(prev))
                goto err2;
+
+       /* Another cpu may race to insert the element with the same key */
+       if (prev) {
+               nft_set_elem_destroy(set, he, true);
+               he = prev;
+       }
+
 out:
        *ext = &he->ext;
        return true;
-- 
2.1.4