linux-kernel - Re: [PATCH net-next] netfilter: nf_tables: avoid excessive stack usage

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Message-ID: <20190907180754.dz7gstqfj7djlbrs@salvia>
Date:   Sat, 7 Sep 2019 20:07:54 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        wenxu <wenxu@...oud.cn>, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] netfilter: nf_tables: avoid excessive stack
 usage

Hi Arnd,

On Fri, Sep 06, 2019 at 05:12:30PM +0200, Arnd Bergmann wrote:
> The nft_offload_ctx structure is much too large to put on the
> stack:
> 
> net/netfilter/nf_tables_offload.c:31:23: error: stack frame size of 1200 bytes in function 'nft_flow_rule_create' [-Werror,-Wframe-larger-than=]
> 
> Use dynamic allocation here, as we do elsewhere in the same
> function.
>
> Fixes: c9626a2cbdb2 ("netfilter: nf_tables: add hardware offload support")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> Since we only really care about two members of the structure, an
> alternative would be a larger rewrite, but that is probably too
> late for v5.4.

Thanks for this patch.

I'm attaching a patch to reduce this structure size a bit. Do you
think this alternative patch is ok until this alternative rewrite
happens? Anyway I agree we should to get this structure away from the
stack, even after this is still large, so your patch (or a variant of
it) will be useful sooner than later I think.

View attachment "x.patch" of type "text/x-diff" (486 bytes)