Re: [PATCH nf] netfilter: nf_tables: fix missmatch in big-endian system

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

On Wed, Mar 08, 2017 at 10:54:18PM +0800, Liping Zhang wrote:
> From: Liping Zhang <zlpnobody@gmail.com>
> 
> Currently, there are two different methods to store an u16 integer to
> the u32 data register. For example:
>   u32 *dest = &regs->data[priv->dreg];
>   1. *dest = 0; *(u16 *) dest = val_u16;
>   2. *dest = val_u16;
> 
> For method 1, the u16 value will be stored like this, either in
> big-endian or little-endian system:
>   0          15           31
>   +-+-+-+-+-+-+-+-+-+-+-+-+
>   |   Value   |     0     |
>   +-+-+-+-+-+-+-+-+-+-+-+-+
> 
> For method 2, in little-endian system, the u16 value will be the same
> as listed above. But in big-endian system, the u16 value will be stored
> like this:
>   0          15           31
>   +-+-+-+-+-+-+-+-+-+-+-+-+
>   |     0     |   Value   |
>   +-+-+-+-+-+-+-+-+-+-+-+-+
> 
> So later we use "memcmp(&regs->data[priv->sreg], data, 2);" to do
> compare in nft_cmp, nft_lookup expr ..., method 2 will get the wrong
> result in big-endian system, as 0~15 bits will always be zero.
> 
> For the similar reason, when loading an u16 value from the u32 data
> register, we should use "*(u16 *) sreg;" instead of "(u16)*sreg;",
> the 2nd method will get the wrong value in the big-endian system.
> 
> So introduce some wrapper functions to store/load an u8 or u16
> integer to/from the u32 data register, and use them in the right
> place.

Applied, thanks.