[PATCH nf] netfilter: nf_tables: fix set->nelem leak

[Pablo Neira Ayuso <pablo@netfilter.org>]

If no NLM_F_EXCL is specified and the element already exists, no error
is reported to userspace. However, no new element is added so decrement
set->nelem to restore it the early increment that nf_tables_newsetelem()
performs.

Fixes: c016c7e45ddf ("netfilter: nf_tables: honor NLM_F_EXCL flag in set element insertion")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 net/netfilter/nf_tables_api.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index 091d2dcc63b2..a4619cbf2fe2 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -3734,8 +3734,10 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 			     nft_set_ext_exists(ext2, NFT_SET_EXT_OBJREF) &&
 			     *nft_set_ext_obj(ext) != *nft_set_ext_obj(ext2)))
 				err = -EBUSY;
-			else if (!(nlmsg_flags & NLM_F_EXCL))
+			else if (!(nlmsg_flags & NLM_F_EXCL)) {
+				atomic_dec(&set->nelems);
 				err = 0;
+			}
 		}
 		goto err5;
 	}
-- 
2.1.4