samples/rust: add netfilter sample

samples/rust/Kconfig

@@ -120,6 +120,16 @@ config SAMPLE_RUST_PLATFORM
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_NETFILTER
+	tristate "Network filter module"
+	help
+	  This option builds the Rust netfilter module sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_netfilter.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_HOSTPROGS
 	bool "Host programs"
 	help

samples/rust/Makefile

@@ -11,5 +11,6 @@ obj-$(CONFIG_SAMPLE_RUST_SEMAPHORE)		+= rust_semaphore.o
 obj-$(CONFIG_SAMPLE_RUST_SEMAPHORE_C)		+= rust_semaphore_c.o
 obj-$(CONFIG_SAMPLE_RUST_RANDOM)		+= rust_random.o
 obj-$(CONFIG_SAMPLE_RUST_PLATFORM)		+= rust_platform.o
+obj-$(CONFIG_SAMPLE_RUST_NETFILTER)		+= rust_netfilter.o
 
 subdir-$(CONFIG_SAMPLE_RUST_HOSTPROGS)		+= hostprogs

samples/rust/rust_netfilter.rs

@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust netfilter sample.
+
+use kernel::net;
+use kernel::net::filter::{self as netfilter, inet, Disposition, Family};
+use kernel::prelude::*;
+
+module! {
+    type: RustNetfilter,
+    name: b"rust_netfilter",
+    author: b"Rust for Linux Contributors",
+    description: b"Rust netfilter sample",
+    license: b"GPL v2",
+}
+
+struct RustNetfilter {
+    _in: Pin<Box<netfilter::Registration<Self>>>,
+    _out: Pin<Box<netfilter::Registration<Self>>>,
+}
+
+impl netfilter::Filter for RustNetfilter {
+    fn filter(_: (), skb: &net::SkBuff) -> Disposition {
+        let data = skb.head_data();
+        pr_info!(
+            "packet headlen={}, len={}, first bytes={:02x?}\n",
+            data.len(),
+            skb.len(),
+            &data[..core::cmp::min(10, data.len())]
+        );
+        Disposition::Accept
+    }
+}
+
+impl kernel::Module for RustNetfilter {
+    fn init(_name: &'static CStr, _module: &'static ThisModule) -> Result<Self> {
+        Ok(Self {
+            _in: netfilter::Registration::new_pinned(
+                Family::INet(inet::Hook::PreRouting),
+                0,
+                net::init_ns().into(),
+                None,
+                (),
+            )?,
+            _out: netfilter::Registration::new_pinned(
+                Family::INet(inet::Hook::PostRouting),
+                0,
+                net::init_ns().into(),
+                None,
+                (),
+            )?,
+        })
+    }
+}