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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Pablo Neira Ayuso <pablo@netfilter.org>
Subject: [PATCH 5.10 30/84] netfilter: nft_dynset: restore set element counter when failing to update
Date:   Tue,  5 Jul 2022 13:57:53 +0200
Message-Id: <20220705115616.204110847@linuxfoundation.org>
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From: Pablo Neira Ayuso <pablo@netfilter.org>

commit 05907f10e235680cc7fb196810e4ad3215d5e648 upstream.

This patch fixes a race condition.

nft_rhash_update() might fail for two reasons:

- Element already exists in the hashtable.
- Another packet won race to insert an entry in the hashtable.

In both cases, new() has already bumped the counter via atomic_add_unless(),
therefore, decrement the set element counter.

Fixes: 22fe54d5fefc ("netfilter: nf_tables: add support for dynamic set updates")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/netfilter/nft_set_hash.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/net/netfilter/nft_set_hash.c
+++ b/net/netfilter/nft_set_hash.c
@@ -142,6 +142,7 @@ static bool nft_rhash_update(struct nft_
 	/* Another cpu may race to insert the element with the same key */
 	if (prev) {
 		nft_set_elem_destroy(set, he, true);
+		atomic_dec(&set->nelems);
 		he = prev;
 	}
 
@@ -151,6 +152,7 @@ out:
 
 err2:
 	nft_set_elem_destroy(set, he, true);
+	atomic_dec(&set->nelems);
 err1:
 	return false;
 }