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

[Julian Anastasov <ja@ssi.bg>]

	Hello,

On Fri, 18 Sep 2026, Julian Anastasov wrote:

> 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>

	Patch is ok but needs to be resent with
the other patch:

pw-bot: changes-requested

> > 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>