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

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Date:   Fri, 10 Feb 2023 11:32:50 +0100
From:   Florian Westphal <fw@...len.de>
To:     Hangyu Hua <hbh25y@...il.com>
Cc:     pablo@...filter.org, kadlec@...filter.org, fw@...len.de,
        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()

Hangyu Hua <hbh25y@...il.com> wrote:
> nf_ct_put() needs to be called to put the refcount got by
> nf_conntrack_find_get() to avoid refcount leak when
> nf_conntrack_hash_check_insert() fails.
> 
> Fixes: 7d367e06688d ("netfilter: ctnetlink: fix soft lockup when netlink adds new entries (v2)")
> Signed-off-by: Hangyu Hua <hbh25y@...il.com>
> ---
>  net/netfilter/nf_conntrack_netlink.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
> index 1286ae7d4609..ca4d5bb1ea52 100644
> --- a/net/netfilter/nf_conntrack_netlink.c
> +++ b/net/netfilter/nf_conntrack_netlink.c
> @@ -2375,12 +2375,15 @@ ctnetlink_create_conntrack(struct net *net,
>  
>  	err = nf_conntrack_hash_check_insert(ct);
>  	if (err < 0)
> -		goto err2;
> +		goto err3;

Ouch, looks like this is broken in more than one way?

nf_conntrack_hash_check_insert() can call nf_ct_kill()
and return an error, in that case ct->master reference
is already dropped for us.

One way would be to return 0 in that case (in
nf_conntrack_hash_check_insert()).  What do you think?