[PATCH net-next] calipso: hash the cache key, not the option start, in calipso_cache_add()

[Daniel Machon]

> calipso_cache_add() stores calipso_ptr + 2 as the cache key, but
> computes entry->hash over calipso_ptr, i.e. starting two bytes earlier
> at the option type and length.  calipso_opt_getattr() looks entries up
> with calipso_cache_check(calipso + 2, calipso[1], ...), which hashes the
> key itself.
> 
> The two hashes only match on a jhash collision, so the CALIPSO label
> cache never hits and every labelled packet takes the full DOI lookup and
> category conversion path.  The memcmp() on the key keeps lookups
> correct, so this is a performance bug only.
> 
> Hash the stored key, as cipso_v4_cache_add() does for CIPSO.

FWIW:

I tested this with a small throwaway KUnit test: put 16 labels into the cache,
then look each one up again the same way the kernel does when a packet arrives.
Without the patch none of them were found (0/16), with it all of them were
(16/16).

Reviewed-by: Daniel Machon <daniel.machon at microchip.com>