From 2f9d3db08d3f2ec55f4c2025613f3678f6bacaf7 Mon Sep 17 00:00:00 2001
From: Marc Schoolderman <marc@tweedegolf.com>
Date: Mon, 2 Sep 2024 17:28:34 +0200
Subject: [PATCH] add more Rustified version of kernel_check

---
 src/common/error.rs  |  2 +-
 src/sudo/mod.rs      |  2 +-
 src/system/kernel.rs | 62 +++++++++++++++++++++++++-------------------
 3 files changed, 37 insertions(+), 29 deletions(-)

diff --git a/src/common/error.rs b/src/common/error.rs
index 711402814..3f243a988 100644
--- a/src/common/error.rs
+++ b/src/common/error.rs
@@ -57,7 +57,7 @@ impl fmt::Display for Error {
             Error::SelfCheck => {
                 f.write_str("sudo must be owned by uid 0 and have the setuid bit set")
             }
-            Error::KernelCheck => f.write_str("sudo needs a Kernel >= 5.9"),
+            Error::KernelCheck => f.write_str("sudo-rs needs a Linux kernel newer than v5.9"),
             Error::CommandNotFound(p) => write!(f, "'{}': command not found", p.display()),
             Error::InvalidCommand(p) => write!(f, "'{}': invalid command", p.display()),
             Error::UserNotFound(u) => write!(f, "user '{u}' not found"),
diff --git a/src/sudo/mod.rs b/src/sudo/mod.rs
index 07264bf5e..947d784e1 100644
--- a/src/sudo/mod.rs
+++ b/src/sudo/mod.rs
@@ -111,7 +111,7 @@ fn sudo_process() -> Result<(), Error> {
     dev_info!("development logs are enabled");
 
     self_check()?;
-    kernel_check(5, 9)?;
+    kernel_check()?;
 
     let pipeline = Pipeline {
         policy: SudoersPolicy::default(),
diff --git a/src/system/kernel.rs b/src/system/kernel.rs
index 070cf6c57..99f0d8cd4 100644
--- a/src/system/kernel.rs
+++ b/src/system/kernel.rs
@@ -1,41 +1,49 @@
 use std::ffi::CStr;
 
-use std::mem::zeroed;
+use std::mem::MaybeUninit;
 
-use crate::common::Error;
+use crate::{common::Error, cutils::cerr};
 
-pub fn kernel_check(major: u32, minor: u32) -> Result<(), Error> {
-    if cfg!(target_os = "freebsd") {
-        return Ok(());
-    }
+#[cfg(target_os = "linux")]
+pub fn kernel_check() -> Result<(), Error> {
+    // On Linux, we need kernel version 5.9 to have access to `close_range()`
+    const TARGET_VERSION: (u32, u32) = (5, 9);
 
-    let mut utsname: libc::utsname = unsafe { zeroed() };
+    let mut utsname = MaybeUninit::uninit();
 
-    if unsafe { libc::uname(&mut utsname) } != 0 {
-        // Could not get the kernel version. Try to run anyway
-        return Ok(());
-    }
+    // SAFETY: uname is passed a correct pointer
+    cerr(unsafe { libc::uname(utsname.as_mut_ptr()) })?;
 
-    let release = unsafe { CStr::from_ptr(utsname.release.as_ptr()) }
-        .to_string_lossy()
-        .into_owned();
+    // SAFETY: since uname exited normally, the struct is now initialized
+    let utsname = unsafe { utsname.assume_init() };
 
-    let version_parts: Vec<&str> = release.split('.').collect();
-
-    if version_parts.len() < 2 {
-        // Could not get the kernel version. Try to run anyway
-        return Ok(());
-    }
+    // SAFETY: utsname.release will hold a null-terminated C string
+    let release = unsafe { CStr::from_ptr(utsname.release.as_ptr()) }.to_string_lossy();
 
     // Parse the major and minor version numbers
-    if let (Ok(major_version), Ok(minor_version)) = (
-        version_parts[0].parse::<u32>(),
-        version_parts[1].parse::<u32>(),
-    ) {
-        if major_version > major || (major_version == major && minor_version >= minor) {
-            return Ok(());
+    let mut version_parts = release.split('.').map_while(|x| x.parse::<u32>().ok());
+
+    match (version_parts.next(), version_parts.next()) {
+        (Some(major), Some(minor)) if (major, minor) < TARGET_VERSION => {
+            // We have determined that this Linux kernel is too old.
+            Err(Error::KernelCheck)
+        }
+        _ => {
+            // We have not been able to prove that sudo-rs is incompatible with this kernel
+            // and are giving the benefit of the doubt.
+            Ok(())
         }
     }
+}
+
+#[cfg(target_os = "freebsd")]
+pub fn kernel_check() -> Result<(), Error> {
+    // the kernel check doesn't make much sense on FreeBSD (we need FreeBSD 8.0 or newer,
+    // which is comparatively ancient compared to Linux 5.9)
+    Ok(())
+}
 
-    Err(Error::KernelCheck)
+#[cfg(not(any(target_os = "freebsd", target_os = "linux")))]
+pub fn kernel_check() -> Result<(), Error> {
+    compile_error!("sudo-rs only works on Linux and FreeBSD");
 }