rhashtable: add rhashtable_lookup_get_insert_key()

This patch modifies __rhashtable_insert_fast() so it returns the
existing object that clashes with the one that you want to insert.
In case the object is successfully inserted, NULL is returned.
Otherwise, you get an error via ERR_PTR().

This patch adapts the existing callers of __rhashtable_insert_fast()
so they handle this new logic, and it adds a new
rhashtable_lookup_get_insert_key() interface to fetch this existing
object.

nf_tables needs this change to improve handling of EEXIST cases via
honoring the NLM_F_EXCL flag and by checking if the data part of the
mapping matches what we have.

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 7 insertions, 3 deletions

diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 5d845ffd7982..7a940d92f17e 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -438,7 +438,8 @@ EXPORT_SYMBOL_GPL(rhashtable_insert_rehash);
 struct bucket_table *rhashtable_insert_slow(struct rhashtable *ht,
                                             const void *key,
                                             struct rhash_head *obj,
-                                            struct bucket_table *tbl)
+                                            struct bucket_table *tbl,
+                                            void **data)
 {
         struct rhash_head *head;
         unsigned int hash;
@@ -449,8 +450,11 @@ struct bucket_table *rhashtable_insert_slow(struct rhashtable *ht,
         spin_lock_nested(rht_bucket_lock(tbl, hash), SINGLE_DEPTH_NESTING);
 
         err = -EEXIST;
-        if (key && rhashtable_lookup_fast(ht, key, ht->p))
-                goto exit;
+        if (key) {
+                *data = rhashtable_lookup_fast(ht, key, ht->p);
+                if (*data)
+                        goto exit;
+        }
 
         err = -E2BIG;
         if (unlikely(rht_grow_above_max(ht, tbl)))