Messages in this thread | | | Subject | Re: Minor IPSec bug + solution | From | Martin Bouzek <> | Date | 17 Sep 2004 11:26:13 +0200 |
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On Thu, 2004-09-16 at 23:19, Herbert Xu wrote: > Martin Bouzek <martin.bouzek@radas-atc.cz> wrote: > > > > I was setting up an VPN via IPSec in kernel 2.6.x on IPv4 and found the > > following bug. It is not possible to set up an IPComp/ESP tunnel with > > IPComp set as mandatory. The following setup works fine for me: > > You can never set IPComp as mandatory because ipcomp_output() will not > compress anything that is incompressible.
Sure. I receive IP-IP packets and they are checked with the same rules as IPComp.
> > > function. For tunnels it returns > > > > tmpl->optional && !xfrm_state_addr_cmp(tmpl, x, family); > > The check is correct as it is. Internal states must never match any > required transform.
Well, I am not expierienced with the networking kernel code, nevertheless I still think the check is not correct.
As I understand it, xfrm_state_addr_cmp returns 0 when tmpl->saddr is 0.0.0.0 (ipv4) or when tmpl->saddr.a4 == x->props.saddr.a4, that is why there is the "!" before it. The "xfrm_state_ok" itself returns nonzero if the tmpl matches the state. In such case the "xfrm_policy_ok" will return index to next state in sec_path. If no matching state is found the "xfrm_policy_ok" returns -1 (if not tmpl->optional) and in such case "__xfrm_policy_check" returns 0 and packet is rejected.
So the following happens for me when packet is received for mandatory IPComp tunnel:
With my setup the pol->xfrm_nr is 1 and sp->len is 1 (in "__xfrm_policy_check" context). "xfrm_policy_ok" is called and it calls the "xfrm_state_ok". x->tunnel_users is 2 - so the "tmpl->optional && !xfrm_state_addr_cmp(tmpl, x, family)" is returned. Because tmpl->optional is set to 0 (required IPComp), xfrm_state_addr_cmp is not called at all and "xfrm_state_ok" returns 0. Because sp->x[idx].xvec->props.mode is set, "xfrm_policy_ok" returns -1 (again tmpl->optional is 0). And so "__xfrm_policy_check" returns 0 and packet is droped.
If you are still not convinced, please look at the xfrm_state_ok and the part for non-tunnel. It clearly returns 1 when the tmpl and x matches.
Moreover with "tmpl->optional || !xfrm_state_addr_cmp(tmpl, x, family);" in "xfrm_state_ok" I can set up the mandatory IPComp without problems. I am not sure there are not any side effects, but it seems ok to me.
Regards
Martin Bouzek - martin.bouzek@radas-atc.cz
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