On Thu, Mar 22, 2007 at 08:39:04AM -0700, Nikolaos D. Bougalis ([EMAIL
PROTECTED]) wrote:
> This particular hash seems to be the odd-man out, since most other
> network related hashes in the kernel seem to be Jenkins-based, and some use
> tagged hashing to defeat algorithmic complexity attacks. For example, the
> route hash uses this:
It seems you do not know a history...
It is the fastest and actually the best hash for that workloads where it
is used, but unfortunately it is too simple for attacker to predict end
result.
> static unsigned int rt_hash_rnd;
>
> static unsigned int rt_hash_code(u32 daddr, u32 saddr)
> {
> return (jhash_2words(daddr, saddr, rt_hash_rnd)
> & rt_hash_mask);
> }
>
> With this in mind, I propose the following replacement for inet_ehashfn,
> which defeats algorithmic complexity attacks and achieves excellent
> distribution:
>
> unsigned int inet_ehashfn(const __be32 laddr, const __u16 lport,
> const __be32 faddr, const __be16 fport)
> {
> return jhash_3words((__force __u32)faddr, (__force __u32)laddr,
> (((__force __u32)fport) << 16) + lport,
> inet_ehash_rnd);
> }
And this is utterly broken. For more details please read netdev@
archives and trivial analysis of jhash_3words().
We can use jhash_2words(laddr, faddr, portpair^inet_ehash_rnd) though.
--
Evgeniy Polyakov
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