jamal wrote:
On Wed, 2005-01-19 at 15:22, Patrick McHardy wrote:
This does not help. Netfilter calls skb_ip_make_writable if it has to
touch the packet, if it is shared or cloned the packet will be copied.
for ipt, just restore:
if (pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
return -ENOMEM
for the rest, the action code will handle all just fine. There will only
be one copy per serious of tramplings. This is design intent.
It seems to be more clever than I initially realized :) But it does need
some fixing for ipt. The ->act function takes a struct sk_buff **, which
implies the skb might get replaced, but tcf_action_exec only takes a struct
sk_buff * and doesn't own the skb. So if the skb is replaced in the action
the owner ends up with a pointer to freed memory. pskb_expand_head is not
enough to stop netfilter from copying, at ingress the the skb might be
nonlinear, in which case it is copied. On egress it seems fine.
Give me some examples which show something is broken then we can have a
more coherent discussion. I am willing to kill ipt if it is the problem.
Instead of killing ipt we could teach netfilter to be smarter about this.
If the data that needs to be mangled is in the non-linear range we could
just linearize the skb. Additionally we should change act_api to only pass
single skb pointers around, to avoid all confusion and possible trouble.
This seems a lot better than changing almost entire net/sched to pass
double pointers around :)
Regards
Patrick
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