On Thu, 2013-05-02 at 09:59 +0200, Jesper Dangaard Brouer wrote:

On Wed, 24 Apr 2013 17:00:30 -0700 Eric Dumazet [off-list ref] wrote:

quoted

On Wed, 2013-04-24 at 17:48 +0200, Jesper Dangaard Brouer wrote:

quoted

This reverts commit 5a3da1fe9561828d0ca7eca664b16ec2b9bf0055.

The problem with commit 5a3da1fe (inet: limit length of fragment
queue hash table bucket lists) is that, once we hit the hash depth
limit (of 128), the we *keep* the existing frag queues, not
allowing new frag queues to be created.  Thus, an attacker can
effectivly block handling of fragments for 30 sec (as each frag
queue have a timeout of 30 sec)

I do not think its good to revert this patch. It was a step in right
direction.

We need a revert, because we are too close to the merge window, and
cannot complete the needed "steps" to make this patch safe, sorry.

Again, a limit of 128 is totally OK. Its in fact too big.

128 cache misses consume 5 us

Allowing a chain being non limited is a more severe bug.

Reverting will allow an attacker to consume all your cpu cycles.

We changed INETFRAGS_HASHSZ to 1024, so 128*1024 max frags is already a
very big limit.

No matter what we do, we need to limit both :

- Memory consumption
- Cpu consumption

For people willing to allow more memory to be used, the only way is to
resize hash table, or using a bigger INETFRAGS_HASHSZ

I do not think there is a hurry, current defrag code is already better
than what we had years ago.