On 28 Mar 2007 16:14:17 +0200
Andi Kleen <[EMAIL PROTECTED]> wrote:
> TCP tends to be initialized early before there is anything
> good in the entropy pool.
>
> static void init_std_data(struct entropy_store *r)
> {
> struct timeval tv;
> unsigned long flags;
>
> spin_lock_irqsave(&r->lock, flags);
> r->entropy_count = 0;
> spin_unlock_irqrestore(&r->lock, flags);
>
> do_gettimeofday(&tv);
> add_entropy_words(r, (__u32 *)&tv, sizeof(tv)/4);
> add_entropy_words(r, (__u32 *)utsname(),
> sizeof(*(utsname()))/4);
> }
>
> utsname is useless here because it runs before user space has
> a chance to set it. The only truly variable thing is the
> boot time, which can be guessed with the ns part being brute forced.
>
> To make it secure you would need to do regular rehash like
> the routing cache which would pick up true randomness on the first
> rehash.
Good point, but :
1) We can now use "struct timespec" to get more bits in init_std_data()
2) tcp ehash salt is initialized at first socket creation, not boot time. Maybe
we have more available entropy at this point.
3) We dont want to be 'totally secure'. We only want to raise the level, and
eventually see if we have to spend more time on this next year(s). AFAIK we had
two different reports from people being hit by the flaw of previous hash. Not
really a critical issue.
4) We could add a hard limit on the length of one chain. Even if the bad guys
discover a flaw, it wont hurt too much.
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