Re: [PATCH] filter: add SKF_AD_NLATTR_NEST to look for nested attributes

[Patrick McHardy <kaber@trash.net>]

Pablo Neira Ayuso wrote:
> SKF_AD_NLATTR allows us to find the first matching attribute in a
> stream of netlink attributes from one offset to the end of the
> netlink message. This is not suitable to look for a specific
> matching inside a set of nested attributes.
> 
> For example, in ctnetlink messages, if we look for the CTA_V6_SRC
> attribute in a message that talks about an IPv4 connection,
> SKF_AD_NLATTR returns the offset of CTA_STATUS which has the same
> value of CTA_V6_SRC but outside the nest. To differenciate
> CTA_STATUS and CTA_V6_SRC, we would have to make assumptions on the
> size of the attribute and the usual offset, resulting in horrible
> BSF code.
> 
> This patch adds SKF_AD_NLATTR_NEST, which is a variant of
> SKF_AD_NLATTR, that looks for an attribute inside the limits of
> a nested attributes, but not further.
> 
> This patch validates that we have enough room to look for the
> nested attributes - based on a suggestion from Patrick McHardy.

Looks good, thanks Pablo.

Acked-by: Patrick McHardy <kaber@trash.net>