Re: [PATCH net v2 2/2] ipvs: reject FTP control ports as data ports

[Julian Anastasov <ja@ssi.bg>]

	Hello,

On Thu, 17 Sep 2026, Zihan Xi wrote:

> ip_vs_ftp_out() creates a wildcard data connection from the
> server-advertised passive port. If that port is one of the configured FTP
> control ports, ip_vs_conn_new() binds the FTP helper to the new connection
> again. A subsequent wildcard lookup can then extend a controlled-connection
> chain.
> 
> Reject zero and configured control ports before creating passive
> connections. For active mode, reject a zero client port and a data port
> derived from a configured control port.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Cc: stable@vger.kernel.org
> Reported-by: Vega <vega@nebusec.ai>
> Assisted-by: LLM
> Co-developed-by: Luxing Yin <root@tr0jan.top>
> Signed-off-by: Luxing Yin <root@tr0jan.top>
> Signed-off-by: Zihan Xi <zihanx@nebusec.ai>

	Patch looks good to me for the nf tree, thanks!

Signed-off-by: Julian Anastasov <ja@ssi.bg>

> ---
> changes in v2:
>   - Reject the data port derived from a configured control port in
>     ip_vs_ftp_in() to cover the active-mode bypass.
>   - v1 Link:
>     https://lore.kernel.org/all/cover.1789110326.git.zihanx@nebusec.ai/
> 
>  net/netfilter/ipvs/ip_vs_ftp.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/net/netfilter/ipvs/ip_vs_ftp.c b/net/netfilter/ipvs/ip_vs_ftp.c
> index 9e3e005a82635..4822a1a75212d 100644
> --- a/net/netfilter/ipvs/ip_vs_ftp.c
> +++ b/net/netfilter/ipvs/ip_vs_ftp.c
> @@ -62,6 +62,17 @@ static unsigned short ports[IP_VS_APP_MAX_PORTS] = {21, 0};
>  module_param_array(ports, ushort, &ports_count, 0444);
>  MODULE_PARM_DESC(ports, "Ports to monitor for FTP control commands");
>  
> +static bool is_control_port(u16 port)
> +{
> +	unsigned int i;
> +
> +	for (i = 0; i < ports_count; i++) {
> +		if (ports[i] == port)
> +			return true;
> +	}
> +	return false;
> +}
> +
>  
>  static char *ip_vs_ftp_data_ptr(struct sk_buff *skb, struct ip_vs_iphdr *ipvsh)
>  {
> @@ -319,6 +330,10 @@ static int ip_vs_ftp_out(struct ip_vs_app *app, struct ip_vs_conn *cp,
>  		return 1;
>  	}
>  
> +	/* Do not redirect data to control ports */
> +	if (!port || is_control_port(ntohs(port)))
> +		return 0;
> +
>  	/* Now update or create a connection entry for it */
>  	{
>  		struct ip_vs_conn_param p;
> @@ -529,6 +544,9 @@ static int ip_vs_ftp_in(struct ip_vs_app *app, struct ip_vs_conn *cp,
>  		return 1;
>  	}
>  
> +	if (!port || is_control_port(ntohs(cp->vport) - 1))
> +		return 0;
> +
>  	/* Passive mode off */
>  	cp->app_data = (void *) IP_VS_FTP_ACTIVE;
>  
> -- 
> 2.43.0

Regards

--
Julian Anastasov <ja@ssi.bg>