When filtering in INPUT or FORWARD within a VRF domain, input interface
matching is done against the VRF device name instead of the real input
interface. This makes interface based filtering difficult if the interface
is associated to a VRF or some other layer 3 master device. While
PREROUTING can match against the real input interface, using it for
filtering is often inconvenient.
To allow filtering in INPUT/FORWARD against the real input interface,
add a match extension for this specific purpose. It is very similar
to the layer 2 slave device match implemented in xt_physdev to match
against bridge ports, but matches on layer 3 slave devices.
As an option, the user may specify a "strict" flag, limiting matches to
interfaces that strictly are layer 3 slave devices.
Signed-off-by: Martin Willi <martin@xxxxxxxxxxxxxx>
---
include/net/ip.h | 2 +-
include/uapi/linux/netfilter/xt_slavedev.h | 18 +++++
net/netfilter/Kconfig | 12 ++++
net/netfilter/Makefile | 1 +
net/netfilter/xt_slavedev.c | 80 ++++++++++++++++++++++
5 files changed, 112 insertions(+), 1 deletion(-)
create mode 100644 include/uapi/linux/netfilter/xt_slavedev.h
create mode 100644 net/netfilter/xt_slavedev.c
diff --git a/include/net/ip.h b/include/net/ip.h
index 5b317c9f4470..12cd3971f4cf 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -98,7 +98,7 @@ static inline void ipcm_init_sk(struct ipcm_cookie *ipcm,
#define PKTINFO_SKB_CB(skb) ((struct in_pktinfo *)((skb)->cb))
/* return enslaved device index if relevant */
-static inline int inet_sdif(struct sk_buff *skb)
+static inline int inet_sdif(const struct sk_buff *skb)
{
#if IS_ENABLED(CONFIG_NET_L3_MASTER_DEV)
if (skb && ipv4_l3mdev_skb(IPCB(skb)->flags))
diff --git a/include/uapi/linux/netfilter/xt_slavedev.h b/include/uapi/linux/netfilter/xt_slavedev.h
new file mode 100644
index 000000000000..d35785b04c4b
--- /dev/null
+++ b/include/uapi/linux/netfilter/xt_slavedev.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_XT_SLAVEDEV_H
+#define _UAPI_XT_SLAVEDEV_H
+
+#include <linux/types.h>
+#include <linux/if.h>
+
+#define XT_SLAVEDEV_IN_INV 0x01 /* invert interface match */
+#define XT_SLAVEDEV_IN_STRICT 0x02 /* require iif to be enslaved */
+#define XT_SLAVEDEV_MASK (0x04 - 1)
+
+struct xt_slavedev_info {
+ char iniface[IFNAMSIZ];
+ unsigned char iniface_mask[IFNAMSIZ];
+ __u8 flags;
+};
+
+#endif /* _UAPI_XT_SLAVEDEV_H */
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 91efae88e8c2..a259192bdb2e 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -1530,6 +1530,18 @@ config NETFILTER_XT_MATCH_SCTP
If you want to compile it as a module, say M here and read
<file:Documentation/kbuild/modules.rst>. If unsure, say `N'.
+config NETFILTER_XT_MATCH_SLAVEDEV
+ tristate '"slavedev" match support'
+ depends on NET_L3_MASTER_DEV
+ depends on NETFILTER_ADVANCED
+ help
+ Slavedev packet matching matches against the input slave interface
+ if the IP packet arrived on a layer 3 master device. It allows
+ matching against the input interface if that interface is
+ associated to a VRF master device.
+
+ To compile it as a module, choose M here. If unsure, say N.
+
config NETFILTER_XT_MATCH_SOCKET
tristate '"socket" match support'
depends on NETFILTER_XTABLES
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index 5e9b2eb24349..9650d1d5216c 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -197,6 +197,7 @@ obj-$(CONFIG_NETFILTER_XT_MATCH_RATEEST) += xt_rateest.o
obj-$(CONFIG_NETFILTER_XT_MATCH_REALM) += xt_realm.o
obj-$(CONFIG_NETFILTER_XT_MATCH_RECENT) += xt_recent.o
obj-$(CONFIG_NETFILTER_XT_MATCH_SCTP) += xt_sctp.o
+obj-$(CONFIG_NETFILTER_XT_MATCH_SLAVEDEV) += xt_slavedev.o
obj-$(CONFIG_NETFILTER_XT_MATCH_SOCKET) += xt_socket.o
obj-$(CONFIG_NETFILTER_XT_MATCH_STATE) += xt_state.o
obj-$(CONFIG_NETFILTER_XT_MATCH_STATISTIC) += xt_statistic.o
diff --git a/net/netfilter/xt_slavedev.c b/net/netfilter/xt_slavedev.c
new file mode 100644
index 000000000000..a53466dfb10b
--- /dev/null
+++ b/net/netfilter/xt_slavedev.c
@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <net/ip.h>
+#include <net/ipv6.h>
+#include <linux/module.h>
+#include <linux/netfilter/x_tables.h>
+#include <uapi/linux/netfilter/xt_slavedev.h>
+
+static bool
+slavedev_mt(const struct sk_buff *skb, struct xt_action_param *par)
+{
+ const struct xt_slavedev_info *info = par->matchinfo;
+ struct net_device *sd;
+ unsigned long ret = 1;
+ int sdif = 0;
+
+ switch (xt_family(par)) {
+ case NFPROTO_IPV4:
+ sdif = inet_sdif(skb);
+ break;
+ case NFPROTO_IPV6:
+ sdif = inet6_sdif(skb);
+ break;
+ }
+ if (sdif) {
+ sd = dev_get_by_index_rcu(xt_net(par), sdif);
+ if (sd)
+ ret = ifname_compare_aligned(sd->name, info->iniface,
+ info->iniface_mask);
+ } else if (!(info->flags & XT_SLAVEDEV_IN_STRICT) && xt_in(par)) {
+ ret = ifname_compare_aligned(xt_inname(par), info->iniface,
+ info->iniface_mask);
+ }
+
+ if (!ret ^ !(info->flags & XT_SLAVEDEV_IN_INV))
+ return false;
+
+ return true;
+}
+
+static int slavedev_mt_check(const struct xt_mtchk_param *par)
+{
+ const struct xt_slavedev_info *info = par->matchinfo;
+
+ if (info->flags & ~XT_SLAVEDEV_MASK)
+ return -EINVAL;
+
+ return 0;
+}
+
+static struct xt_match slavedev_mt_reg __read_mostly = {
+ .name = "slavedev",
+ .revision = 0,
+ .family = NFPROTO_UNSPEC,
+ .checkentry = slavedev_mt_check,
+ .match = slavedev_mt,
+ .matchsize = sizeof(struct xt_slavedev_info),
+ .hooks = (1 << NF_INET_LOCAL_IN) |
+ (1 << NF_INET_FORWARD),
+ .me = THIS_MODULE,
+};
+
+static int __init slavedev_mt_init(void)
+{
+ return xt_register_match(&slavedev_mt_reg);
+}
+
+static void __exit slavedev_mt_exit(void)
+{
+ xt_unregister_match(&slavedev_mt_reg);
+}
+
+module_init(slavedev_mt_init);
+module_exit(slavedev_mt_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Martin Willi <martin@xxxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("Xtables: L3master input slave device match");
+MODULE_ALIAS("ipt_slavedev");
+MODULE_ALIAS("ip6t_slavedev");
--
2.20.1
