linux-kernel - Re: [PATCH v1] net/tcp: use kfree_sensitive() instend of kfree() in tcp_md5_twsk_free

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Message-ID: <CANn89iKGqObLBOx-ZMJbYOJ3OSETDestrcf6Yj5HON0Pbda9tA@mail.gmail.com>
Date:   Tue, 7 Nov 2023 04:40:08 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Minjie Du <duminjie@...o.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "open list:NETWORKING [TCP]" <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        opensource.kernel@...o.com
Subject: Re: [PATCH v1] net/tcp: use kfree_sensitive() instend of kfree() in tcp_md5_twsk_free_rcu()

On Tue, Nov 7, 2023 at 3:35 AM Minjie Du <duminjie@...o.com> wrote:
>
> key might contain private information, so better use
> kfree_sensitive to free it.
> In tcp_md5_twsk_free_rcu() use kfree_sensitive().
>
> Signed-off-by: Minjie Du <duminjie@...o.com>
> ---
>  net/ipv4/tcp_minisocks.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
> index a9807eeb311c..a7be78096783 100644
> --- a/net/ipv4/tcp_minisocks.c
> +++ b/net/ipv4/tcp_minisocks.c
> @@ -368,7 +368,7 @@ static void tcp_md5_twsk_free_rcu(struct rcu_head *head)
>         struct tcp_md5sig_key *key;
>
>         key = container_of(head, struct tcp_md5sig_key, rcu);
> -       kfree(key);
> +       kfree_sensitive(key);
>         static_branch_slow_dec_deferred(&tcp_md5_needed);
>         tcp_md5_release_sigpool();
>  }
> --
> 2.39.0
>



1) net-next is currently closed.

2) such patch could send a wrong signal (false sense of security with MD5)

3) You forgot tcp_time_wait_init(), tcp_md5_do_del(), tcp_md5_key_copy(),
    tcp_md5_do_add(), tcp_clear_md5_list().

More work is needed I am afraid, please wait until next week when
6-7-rc1 is tagged and net-next opens again.