netdev - Re: [PATCH] net: netfilter: fix possible refcount leak in ctnetlink_create

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Message-ID: <20230212125320.GA780@breakpoint.cc>
Date:   Sun, 12 Feb 2023 13:53:20 +0100
From:   Florian Westphal <fw@...len.de>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     Florian Westphal <fw@...len.de>, Hangyu Hua <hbh25y@...il.com>,
        kadlec@...filter.org, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: netfilter: fix possible refcount leak in
 ctnetlink_create_conntrack()

Pablo Neira Ayuso <pablo@...filter.org> wrote:
> > One way would be to return 0 in that case (in
> > nf_conntrack_hash_check_insert()).  What do you think?
> 
> This is misleading to the user that adds an entry via ctnetlink?
> 
> ETIMEDOUT also looks a bit confusing to report to userspace.
> Rewinding: if the intention is to deal with stale conntrack extension,
> for example, helper module has been removed while this entry was
> added. Then, probably call EAGAIN so nfnetlink has a chance to retry
> transparently?

Seems we first need to add a "bool *inserted" so we know when the ct
entry went public.

I'll also have a look at switching to a refcount based model for
all extensions that reference external objects, this would avoid
the entire problem, but thats likely more intrusive.