Add wrapper for linux kernel module loading

- init_module and finit_module to load kernel modules
- delete_module to unload kernel modules

Signed-off-by: Pascal Bach <pascal.bach@nextrem.ch>

CHANGELOG.md

@@ -14,6 +14,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#923](https://github.com/nix-rust/nix/pull/923))
 - Added a `dir` module for reading directories (wraps `fdopendir`, `readdir`, and `rewinddir`).
   ([#916](https://github.com/nix-rust/nix/pull/916))
+- Added `kmod` module that allows loading and unloading kernel modules on Linux.
+  ([#930](https://github.com/nix-rust/nix/pull/930))
 
 ### Changed
 - Increased required Rust version to 1.22.1/

src/kmod.rs

@@ -0,0 +1,123 @@
+//! Load and unload kernel modules.
+//!
+//! For more details see
+
+use libc;
+use std::ffi::CStr;
+use std::os::unix::io::AsRawFd;
+
+use errno::Errno;
+use Result;
+
+/// Loads a kernel module from a buffer.
+///
+/// It loads an ELF image into kernel space,
+/// performs any necessary symbol relocations,
+/// initializes module parameters to values provided by the caller,
+/// and then runs the module's init function.
+///
+/// This function requires `CAP_SYS_MODULE` privilege.
+///
+/// The `module_image` argument points to a buffer containing the binary image
+/// to be loaded. The buffer should contain a valid ELF image
+/// built for the running kernel.
+///
+/// The `param_values` argument is a string containing space-delimited specifications
+/// of the values for module parameters.
+/// Each of the parameter specifications has the form:
+///
+/// `name[=value[,value...]]`
+///
+/// # Example
+///
+/// ```no_run
+/// use std::fs::File;
+/// use std::io::Read;
+/// use std::ffi::CString;
+/// use nix::kmod::init_module;
+///
+/// let mut f = File::open("mykernel.ko").unwrap();
+/// let mut contents: Vec<u8> = Vec::new();
+/// f.read_to_end(&mut contents).unwrap();
+/// init_module(&mut contents, &CString::new("who=Rust when=Now,12").unwrap()).unwrap();
+/// ```
+///
+/// See [`man init_module(2)`](http://man7.org/linux/man-pages/man2/init_module.2.html) for more information.
+pub fn init_module(module_image: &[u8], param_values: &CStr) -> Result<()> {
+    let res = unsafe {
+        libc::syscall(
+            libc::SYS_init_module,
+            module_image.as_ptr(),
+            module_image.len(),
+            param_values.as_ptr(),
+        )
+    };
+
+    Errno::result(res).map(drop)
+}
+
+libc_bitflags!(
+    /// Flags used by the `finit_module` function.
+    pub struct ModuleInitFlags: libc::c_uint {
+        /// Ignore symbol version hashes.
+        MODULE_INIT_IGNORE_MODVERSIONS;
+        /// Ignore kernel version magic.
+        MODULE_INIT_IGNORE_VERMAGIC;
+    }
+);
+
+/// Loads a kernel module from a given file descriptor.
+///
+/// # Example
+///
+/// ```no_run
+/// use std::fs::File;
+/// use std::ffi::CString;
+/// use nix::kmod::{finit_module, ModuleInitFlags};
+///
+/// let f = File::open("mymod.ko").unwrap();
+/// finit_module(&f, &CString::new("").unwrap(), ModuleInitFlags::empty()).unwrap();
+/// ```
+///
+/// See [`man init_module(2)`](http://man7.org/linux/man-pages/man2/init_module.2.html) for more information.
+pub fn finit_module<T: AsRawFd>(fd: &T, param_values: &CStr, flags: ModuleInitFlags) -> Result<()> {
+    let res = unsafe {
+        libc::syscall(
+            libc::SYS_finit_module,
+            fd.as_raw_fd(),
+            param_values.as_ptr(),
+            flags.bits(),
+        )
+    };
+
+    Errno::result(res).map(drop)
+}
+
+libc_bitflags!(
+    /// Flags used by `delete_module`.
+    ///
+    /// See [`man delete_module(2)`](http://man7.org/linux/man-pages/man2/delete_module.2.html)
+    /// for a detailed description how these flags work.
+    pub struct DeleteModuleFlags: libc::c_int {
+        O_NONBLOCK;
+        O_TRUNC;
+    }
+);
+
+/// Unloads the kernel module with the given name.
+///
+/// # Example
+///
+/// ```no_run
+/// use std::ffi::CString;
+/// use nix::kmod::{delete_module, DeleteModuleFlags};
+///
+/// delete_module(&CString::new("mymod").unwrap(), DeleteModuleFlags::O_NONBLOCK).unwrap();
+/// ```
+///
+/// See [`man delete_module(2)`](http://man7.org/linux/man-pages/man2/delete_module.2.html) for more information.
+pub fn delete_module(name: &CStr, flags: DeleteModuleFlags) -> Result<()> {
+    let res = unsafe { libc::syscall(libc::SYS_delete_module, name.as_ptr(), flags.bits()) };
+
+    Errno::result(res).map(drop)
+}

src/lib.rs

@@ -43,7 +43,11 @@ pub mod fcntl;
           target_os = "netbsd",
           target_os = "openbsd"))]
 pub mod ifaddrs;
-#[cfg(any(target_os = "linux", target_os = "android"))]
+#[cfg(any(target_os = "android",
+          target_os = "linux"))]
+pub mod kmod;
+#[cfg(any(target_os = "android",
+          target_os = "linux"))]
 pub mod mount;
 #[cfg(any(target_os = "dragonfly",
           target_os = "freebsd",
@@ -57,7 +61,8 @@ pub mod net;
 pub mod poll;
 #[deny(missing_docs)]
 pub mod pty;
-#[cfg(any(target_os = "linux", target_os = "android"))]
+#[cfg(any(target_os = "android",
+          target_os = "linux"))]
 pub mod sched;
 pub mod sys;
 // This can be implemented for other platforms as soon as libc

test/sys/test_select.rs

@@ -2,7 +2,6 @@ use nix::sys::select::*;
 use nix::unistd::{pipe, write};
 use nix::sys::signal::SigSet;
 use nix::sys::time::{TimeSpec, TimeValLike};
-use std::os::unix::io::RawFd;
 
 #[test]
 pub fn test_pselect() {

test/test.rs

@@ -27,6 +27,9 @@ macro_rules! skip_if_not_root {
 mod sys;
 mod test_dir;
 mod test_fcntl;
+#[cfg(any(target_os = "android",
+          target_os = "linux"))]
+mod test_kmod;
 #[cfg(any(target_os = "dragonfly",
           target_os = "freebsd",
           target_os = "fushsia",

test/test_kmod/hello_mod/Makefile

@@ -0,0 +1,7 @@
+obj-m += hello.o
+
+all:
+	make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) modules
+
+clean:
+	make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) clean

test/test_kmod/hello_mod/hello.c

@@ -0,0 +1,26 @@
+/*
+ *  SPDX-License-Identifier: GPL-2.0+ or MIT
+ */
+#include <linux/module.h>
+#include <linux/kernel.h>
+
+static int number= 1;
+static char *who = "World";
+
+module_param(number, int, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
+MODULE_PARM_DESC(myint, "Just some number");
+module_param(who, charp, 0000);
+MODULE_PARM_DESC(who, "Whot to greet");
+
+int init_module(void)
+{
+	printk(KERN_INFO "Hello %s (%d)!\n", who, number);
+	return 0;
+}
+
+void cleanup_module(void)
+{
+	printk(KERN_INFO "Goodbye %s (%d)!\n", who, number);
+}
+
+MODULE_LICENSE("Dual MIT/GPL");

test/test_kmod/mod.rs

@@ -0,0 +1,152 @@
+use std::fs::copy;
+use std::path::PathBuf;
+use std::process::Command;
+use tempfile::{tempdir, TempDir};
+
+fn compile_kernel_module() -> (PathBuf, String, TempDir) {
+    let _m = ::FORK_MTX
+        .lock()
+        .expect("Mutex got poisoned by another test");
+
+    let tmp_dir = tempdir().expect("unable to create temporary build directory");
+
+    copy(
+        "test/test_kmod/hello_mod/hello.c",
+        &tmp_dir.path().join("hello.c"),
+    ).expect("unable to copy hello.c to temporary build directory");
+    copy(
+        "test/test_kmod/hello_mod/Makefile",
+        &tmp_dir.path().join("Makefile"),
+    ).expect("unable to copy Makefile to temporary build directory");
+
+    let status = Command::new("make")
+        .current_dir(tmp_dir.path())
+        .status()
+        .expect("failed to run make");
+
+    assert!(status.success());
+
+    // Return the relative path of the build kernel module
+    (tmp_dir.path().join("hello.ko"), "hello".to_owned(), tmp_dir)
+}
+
+use nix::errno::Errno;
+use nix::kmod::{delete_module, DeleteModuleFlags};
+use nix::kmod::{finit_module, init_module, ModuleInitFlags};
+use nix::Error;
+use std::ffi::CString;
+use std::fs::File;
+use std::io::Read;
+
+#[test]
+fn test_finit_and_delete_module() {
+    skip_if_not_root!("test_finit_module");
+
+    let (kmod_path, kmod_name, _kmod_dir) = compile_kernel_module();
+
+    let f = File::open(kmod_path).expect("unable to open kernel module");
+    finit_module(&f, &CString::new("").unwrap(), ModuleInitFlags::empty())
+        .expect("unable to load kernel module");
+
+    delete_module(
+        &CString::new(kmod_name).unwrap(),
+        DeleteModuleFlags::empty(),
+    ).expect("unable to unload kernel module");
+}
+
+#[test]
+fn test_finit_and_delete_modul_with_params() {
+    skip_if_not_root!("test_finit_module_with_params");
+
+    let (kmod_path, kmod_name, _kmod_dir) = compile_kernel_module();
+
+    let f = File::open(kmod_path).expect("unable to open kernel module");
+    finit_module(
+        &f,
+        &CString::new("who=Rust number=2018").unwrap(),
+        ModuleInitFlags::empty(),
+    ).expect("unable to load kernel module");
+
+    delete_module(
+        &CString::new(kmod_name).unwrap(),
+        DeleteModuleFlags::empty(),
+    ).expect("unable to unload kernel module");
+}
+
+#[test]
+fn test_init_and_delete_module() {
+    skip_if_not_root!("test_init_module");
+
+    let (kmod_path, kmod_name, _kmod_dir) = compile_kernel_module();
+
+    let mut f = File::open(kmod_path).expect("unable to open kernel module");
+    let mut contents: Vec<u8> = Vec::new();
+    f.read_to_end(&mut contents)
+        .expect("unable to read kernel module content to buffer");
+    init_module(&mut contents, &CString::new("").unwrap()).expect("unable to load kernel module");
+
+    delete_module(
+        &CString::new(kmod_name).unwrap(),
+        DeleteModuleFlags::empty(),
+    ).expect("unable to unload kernel module");
+}
+
+#[test]
+fn test_init_and_delete_module_with_params() {
+    skip_if_not_root!("test_init_module");
+
+    let (kmod_path, kmod_name, _kmod_dir) = compile_kernel_module();
+
+    let mut f = File::open(kmod_path).expect("unable to open kernel module");
+    let mut contents: Vec<u8> = Vec::new();
+    f.read_to_end(&mut contents)
+        .expect("unable to read kernel module content to buffer");
+    init_module(&mut contents, &CString::new("who=Nix number=2015").unwrap())
+        .expect("unable to load kernel module");
+
+    delete_module(
+        &CString::new(kmod_name).unwrap(),
+        DeleteModuleFlags::empty(),
+    ).expect("unable to unload kernel module");
+}
+
+#[test]
+fn test_finit_module_invalid() {
+    skip_if_not_root!("test_finit_module_invalid");
+
+    let kmod_path = "/dev/zero";
+
+    let f = File::open(kmod_path).expect("unable to open kernel module");
+    let result = finit_module(&f, &CString::new("").unwrap(), ModuleInitFlags::empty());
+
+    assert_eq!(result.unwrap_err(), Error::Sys(Errno::EINVAL));
+}
+
+#[test]
+fn test_finit_module_twice_and_delete_module() {
+    skip_if_not_root!("test_finit_module_twice_and_delete_module");
+
+    let (kmod_path, kmod_name, _kmod_dir) = compile_kernel_module();
+
+    let f = File::open(kmod_path).expect("unable to open kernel module");
+    finit_module(&f, &CString::new("").unwrap(), ModuleInitFlags::empty())
+        .expect("unable to load kernel module");
+
+    let result = finit_module(&f, &CString::new("").unwrap(), ModuleInitFlags::empty());
+
+    assert_eq!(result.unwrap_err(), Error::Sys(Errno::EEXIST));
+
+    delete_module(
+        &CString::new(kmod_name).unwrap(),
+        DeleteModuleFlags::empty(),
+    ).expect("unable to unload kernel module");
+}
+
+#[test]
+fn test_delete_module_not_loaded() {
+    skip_if_not_root!("test_delete_module_not_loaded");
+
+    let result = delete_module(&CString::new("hello").unwrap(), DeleteModuleFlags::empty());
+
+    assert_eq!(result.unwrap_err(), Error::Sys(Errno::ENOENT));
+}