Re: [PATCH 1/1] netfilter: nf_ct_tcp: pack nf_ct_tcp_flags to match user space

[Patrick McHardy <kaber@trash.net>]

Lutz Jaenicke wrote:
> On some platforms (here: Intel IXP4xx ARM big endian)
> sizeof(struct nf_ct_tcp_flags) evaluates to 4 bytes while in the user
> space code 2 bytes is hard coded.
> Add "__attribute__ ((__packed__))" to enforce matching structure
> sizes.
> 
> Signed-off-by: Lutz Jaenicke <ljaenicke@innominate.com>
> ---
>  include/linux/netfilter/nf_conntrack_tcp.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/netfilter/nf_conntrack_tcp.h b/include/linux/netfilter/nf_conntrack_tcp.h
> index 6e135f9..9d4cf26 100644
> --- a/include/linux/netfilter/nf_conntrack_tcp.h
> +++ b/include/linux/netfilter/nf_conntrack_tcp.h
> @@ -42,7 +42,7 @@ enum tcp_conntrack {
>  struct nf_ct_tcp_flags {
>  	__u8 flags;
>  	__u8 mask;
> -};
> +} __attribute__ ((packed));

I would prefer to fix userspace to use sizeof(...) instead of
using packed structs in the kernel. AFAICT, that should also
work on all architectures.