This patch is part of a proposal to add a new filter type to
ebtables that matches on an arbitrary string within the
encapsulated network-layer packet.
The match starts from the beginning of the network-layer packet.
Signed-off-by: Bernie Harris <bernie.harris@xxxxxxxxxxxxxxxxxxx>
---
include/uapi/linux/netfilter_bridge/ebt_string.h | 16 ++++++
net/bridge/netfilter/Kconfig | 8 +++
net/bridge/netfilter/Makefile | 1 +
net/bridge/netfilter/ebt_string.c | 65 ++++++++++++++++++++++++
4 files changed, 90 insertions(+)
create mode 100644 include/uapi/linux/netfilter_bridge/ebt_string.h
create mode 100644 net/bridge/netfilter/ebt_string.c
diff --git a/include/uapi/linux/netfilter_bridge/ebt_string.h b/include/uapi/linux/netfilter_bridge/ebt_string.h
new file mode 100644
index 000000000000..87d04e9efebd
--- /dev/null
+++ b/include/uapi/linux/netfilter_bridge/ebt_string.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef __LINUX_BRIDGE_EBT_STRING_H
+#define __LINUX_BRIDGE_EBT_STRING_H
+
+#include <linux/types.h>
+
+#define EBT_STRING_MATCH "string"
+#define MAX_STRING_OCTETS 64
+
+struct ebt_string_info {
+ __u16 offset;
+ __u16 length;
+ unsigned char string[MAX_STRING_OCTETS + 1];
+};
+
+#endif
diff --git a/net/bridge/netfilter/Kconfig b/net/bridge/netfilter/Kconfig
index e7ef1a1ef3a6..ec1287b3678c 100644
--- a/net/bridge/netfilter/Kconfig
+++ b/net/bridge/netfilter/Kconfig
@@ -154,6 +154,14 @@ config BRIDGE_EBT_VLAN
This option adds the 802.1Q vlan match, which allows the filtering of
802.1Q vlan fields.
+ To compile it as a module, choose M here. If unsure, say N.
+
+config BRIDGE_EBT_STRING
+ tristate "ebt: string filter support"
+ help
+ This option adds the string match, which allows filtering based on
+ an arbitrary sequence of octets starting from a given offset.
+
To compile it as a module, choose M here. If unsure, say N.
#
# targets
diff --git a/net/bridge/netfilter/Makefile b/net/bridge/netfilter/Makefile
index 2f28e16de6c7..450a84ada5e4 100644
--- a/net/bridge/netfilter/Makefile
+++ b/net/bridge/netfilter/Makefile
@@ -28,6 +28,7 @@ obj-$(CONFIG_BRIDGE_EBT_MARK) += ebt_mark_m.o
obj-$(CONFIG_BRIDGE_EBT_PKTTYPE) += ebt_pkttype.o
obj-$(CONFIG_BRIDGE_EBT_STP) += ebt_stp.o
obj-$(CONFIG_BRIDGE_EBT_VLAN) += ebt_vlan.o
+obj-$(CONFIG_BRIDGE_EBT_STRING) += ebt_string.o
# targets
obj-$(CONFIG_BRIDGE_EBT_ARPREPLY) += ebt_arpreply.o
diff --git a/net/bridge/netfilter/ebt_string.c b/net/bridge/netfilter/ebt_string.c
new file mode 100644
index 000000000000..66770506d3a3
--- /dev/null
+++ b/net/bridge/netfilter/ebt_string.c
@@ -0,0 +1,65 @@
+/*
+ * string
+ *
+ * Author:
+ * Bernie Harris bernie.harris@xxxxxxxxxxxxxxxxxxx
+ *
+ * October 2017
+ *
+ */
+#include <linux/module.h>
+#include <linux/netfilter/x_tables.h>
+#include <linux/netfilter_bridge/ebtables.h>
+#include <linux/netfilter_bridge/ebt_string.h>
+
+static bool
+ebt_string_mt(const struct sk_buff *skb, struct xt_action_param *par)
+{
+ const struct ebt_string_info *info = par->matchinfo;
+ unsigned char buf[MAX_STRING_OCTETS + 1];
+ unsigned char *match_start;
+ int i;
+ int offset = skb_network_offset(skb) + info->offset;
+
+ if (offset + info->length >= skb->len)
+ return false;
+
+ match_start = skb_header_pointer(skb, offset, info->length, buf);
+
+ for (i = 0; i < info->length; i++) {
+ if (*(match_start + i) != info->string[i])
+ return false;
+ }
+
+ return true;
+}
+
+static int ebt_string_mt_check(const struct xt_mtchk_param *par)
+{
+ return 0;
+}
+
+static struct xt_match ebt_string_mt_reg __read_mostly = {
+ .name = "string",
+ .revision = 0,
+ .family = NFPROTO_BRIDGE,
+ .match = ebt_string_mt,
+ .checkentry = ebt_string_mt_check,
+ .matchsize = sizeof(struct ebt_string_info),
+ .me = THIS_MODULE,
+};
+
+static int __init ebt_string_init(void)
+{
+ return xt_register_match(&ebt_string_mt_reg);
+}
+
+static void __exit ebt_string_fini(void)
+{
+ xt_unregister_match(&ebt_string_mt_reg);
+}
+
+module_init(ebt_string_init);
+module_exit(ebt_string_fini);
+MODULE_DESCRIPTION("Ebtables: String match");
+MODULE_LICENSE("GPL");
--
2.15.1
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