Re: PROBLEM: Injected conntrack lost helper

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When the conntrack is created, the extension is created before the conntrack is assigned confirmed and inserted into the hash table. But the function ctnetlink_setup_nat() causes loss of helper in the mentioned situation. I mention the template because it's seamless in the __nf_ct_try_assign_helper() function. Please double check.

On 1/31/22 18:20, Florian Westphal wrote:
Pham Thanh Tuyen <phamtyn@xxxxxxxxx> wrote:

[ moving to netfilter-devel ]

My name is Pham Thanh Tuyen. I found a bug related to the ctnetlink
and conntrack subsystems. Details are as follows:

1. Summary: Injected conntrack lost helper

2. Description: When a conntrack whose helper is injected from
userspace, the ctnetlink creates helper for it but NAT then loses
the helper in case the user defined helper explicitly with CT
Hmm.  If you insert a conntrack entry from userspace, it will already
be confirmed, so nat rules will have no effect, and template CT rules
are irrelevant wrt. to the helper, as extension can only be created if
the conntrack is not in the hash yet.

Can you describe the steps to reproduce this bug?

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