netfilter: ctnetlink: disable helper autoassign

When userspace, e.g. conntrackd, inserts an entry with a specified helper,
its possible that the helper is lost immediately after its added:

ctnetlink_create_conntrack
  -> nf_ct_helper_ext_add + assign helper
    -> ctnetlink_setup_nat
      -> ctnetlink_parse_nat_setup
         -> parse_nat_setup -> nfnetlink_parse_nat_setup
	                       -> nf_nat_setup_info
                                 -> nf_conntrack_alter_reply
                                   -> __nf_ct_try_assign_helper

... and __nf_ct_try_assign_helper will zero the helper again.

Set IPS_HELPER bit to bypass auto-assign logic, its unwanted, just like
when helper is assigned via ruleset.

Dropped old 'not strictly necessary' comment, it referred to use of
rcu_assign_pointer() before it got replaced by RCU_INIT_POINTER().

NB: Fixes tag intentionally incorrect, this extends the referenced commit,
but this change won't build without IPS_HELPER introduced there.

Fixes: 6714cf5465d280 ("netfilter: nf_conntrack: fix explicit helper attachment and NAT")
Reported-by: Pham Thanh Tuyen <phamtyn@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/include/uapi/linux/netfilter/nf_conntrack_common.h b/include/uapi/linux/netfilter/nf_conntrack_common.h
index 4b33950..2607102 100644 (file)
--- a/include/uapi/linux/netfilter/nf_conntrack_common.h
+++ b/include/uapi/linux/netfilter/nf_conntrack_common.h
@@ -106,7 +106,7 @@ enum ip_conntrack_status {
        IPS_NAT_CLASH = IPS_UNTRACKED,
 #endif
 
-       /* Conntrack got a helper explicitly attached via CT target. */
+       /* Conntrack got a helper explicitly attached (ruleset, ctnetlink). */
        IPS_HELPER_BIT = 13,
        IPS_HELPER = (1 << IPS_HELPER_BIT),
 

diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index ac43837..7032402 100644 (file)
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -2311,7 +2311,8 @@ ctnetlink_create_conntrack(struct net *net,
                        if (helper->from_nlattr)
                                helper->from_nlattr(helpinfo, ct);
 
-                       /* not in hash table yet so not strictly necessary */
+                       /* disable helper auto-assignment for this entry */
+                       ct->status |= IPS_HELPER;
                        RCU_INIT_POINTER(help->helper, helper);
                }
        } else {