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    Subject[PATCH 4.19 16/33] netfilter: nft_dynset: restore set element counter when failing to update
    Date
    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
    @@ -145,6 +145,7 @@ 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;
    }

    @@ -154,6 +155,7 @@ out:

    err2:
    nft_set_elem_destroy(set, he, true);
    + atomic_dec(&set->nelems);
    err1:
    return false;
    }

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