In the Linux kernel, the following vulnerability has been resolved:

netfilter: synproxy: add mutex to guard hook reference counting

As the synproxy infrastructure register netfilter hooks on-demand when a
user adds the first iptables target or nftables expression, if done
concurrently they can race each other.

Introduce a mutex to serialize the refcount control blocks access from
both frontends. While a per namespace mutex might be more efficient, it
is not needed for target/expression like SYNPROXY.

https://git.kernel.org/stable/c/0ec9ddc1bda261a2c57636c74c8b4e53000102c9

https://git.kernel.org/stable/c/0f8ba5e4c53d2e4a536aa68140beda9fe59b2f88

https://git.kernel.org/stable/c/2fcba19caaeb2a33017459d3430f057967bb91b6

https://git.kernel.org/stable/c/56ffbe3a08c01dcdb0d6adee9ce1e535bfb3b389

https://git.kernel.org/stable/c/640441348258220e78daed40528b85b8afcedab6

https://git.kernel.org/stable/c/aaf80701dc2f7a48fe543961e21f8ca3924d587c

https://git.kernel.org/stable/c/debc57b83d5b323df74bf010c8d50fe26ad2ed6b

https://git.kernel.org/stable/c/fbf0591275f50eae5733c3d7a8cd6c1e79933ffa

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