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

[Pablo Neira Ayuso <pablo@netfilter.org>]

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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@arndb.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.

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diff --git a/include/net/netfilter/nf_tables_offload.h b/include/net/netfilter/nf_tables_offload.h
index db104665a9e4..cc44d29e9fd7 100644
--- a/include/net/netfilter/nf_tables_offload.h
+++ b/include/net/netfilter/nf_tables_offload.h
@@ -5,10 +5,10 @@
 #include <net/netfilter/nf_tables.h>
 
 struct nft_offload_reg {
-	u32		key;
-	u32		len;
-	u32		base_offset;
-	u32		offset;
+	u8		key;
+	u8		len;
+	u8		base_offset;
+	u8		offset;
 	struct nft_data data;
 	struct nft_data	mask;
 };