Re: [PATCH net v2 2/2] ipvs: reject FTP control ports as data ports
From: Julian Anastasov <ja@ssi.bg>
Date: 2026-09-18 16:54:13
Also in:
lkml, lvs-devel, netfilter-devel
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 <redacted>
Assisted-by: LLM
Co-developed-by: Luxing Yin <redacted>
Signed-off-by: Luxing Yin <redacted>
Signed-off-by: Zihan Xi <redacted>Patch looks good to me for the nf tree, thanks! Signed-off-by: Julian Anastasov <ja@ssi.bg>
quoted hunk ↗ jump to hunk
--- 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/ (local) 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 [off-list ref]