On Thu, 02 May 2013 08:16:41 -0700
Eric Dumazet [off-list ref] wrote:

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

quoted

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.

[...]

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.

 
Eric I think we agree that:
 1) we need resizing of hash table based on mem limit
 2) mem limit per netns "blocks" the hash resize patch

Without these two patches/changes, the static 128 depth limit
introduces an undocumented limit on the max mem limit
setting (/proc/sys/net/ipv4/ipfrag_high_thresh).

I think we only disagree on the order of the patches.

But lets keep this, because after we have increased hash
size (INETFRAGS_HASHSZ) to 1024, we have pushed the "undocumented
limit" so-far that is very unlikely to be hit.  We would have to
start >36 netns instances, all being overloaded with small
incomplete fragments at the same time (30 sec time window).

--Jesper