Re: [PATCH] net: Fix potential memory leak in proto_register()

From: Cong Wang <xiyou.wangcong@gmail.com>
To: Miaohe Lin <linmiaohe@huawei.com>
Cc: David Miller <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Eric Dumazet <edumazet@google.com>,
	Martin KaFai Lau <kafai@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Jakub Sitnicki <jakub@cloudflare.com>,
	Kees Cook <keescook@chromium.org>,
	zhang.lin16@zte.com.cn,
	Linux Kernel Network Developers <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] net: Fix potential memory leak in proto_register()
Date: Tue, 11 Aug 2020 16:02:51 -0700	[thread overview]
Message-ID: <CAM_iQpW6R5=J0VPwNimOLJRrhwUh--aknpbksizzs0o6Q-gxFA@mail.gmail.com> (raw)
In-Reply-To: <20200810121658.54657-1-linmiaohe@huawei.com>

On Mon, Aug 10, 2020 at 5:19 AM Miaohe Lin <linmiaohe@huawei.com> wrote:
>
> If we failed to assign proto idx, we free the twsk_slab_name but forget to
> free the twsk_slab. Add a helper function tw_prot_cleanup() to free these
> together and also use this helper function in proto_unregister().
>
> Fixes: b45ce32135d1 ("sock: fix potential memory leak in proto_register()")
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
>  net/core/sock.c | 25 +++++++++++++++----------
>  1 file changed, 15 insertions(+), 10 deletions(-)
>
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 49cd5ffe673e..c9083ad44ea1 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -3406,6 +3406,16 @@ static void sock_inuse_add(struct net *net, int val)
>  }
>  #endif
>
> +static void tw_prot_cleanup(struct timewait_sock_ops *twsk_prot)
> +{
> +       if (!twsk_prot)
> +               return;
> +       kfree(twsk_prot->twsk_slab_name);
> +       twsk_prot->twsk_slab_name = NULL;
> +       kmem_cache_destroy(twsk_prot->twsk_slab);

Hmm, are you sure you can free the kmem cache name before
kmem_cache_destroy()? To me, it seems kmem_cache_destroy()
frees the name via slab_kmem_cache_release() via kfree_const().
With your patch, we have a double-free on the name?

Or am I missing anything?

Thanks.