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netfilter: ctnetlink: disable helper autoassign

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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: 6714cf5465 ("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>
This commit is contained in:
Florian Westphal 2022-02-02 12:00:56 +01:00 committed by Pablo Neira Ayuso
parent 1f6339e034
commit d1ca60efc5
2 changed files with 3 additions and 2 deletions
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2
include/uapi/linux/netfilter/nf_conntrack_common.h
View file

@ -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),

3
net/netfilter/nf_conntrack_netlink.c
View file

@ -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 {