[PATCH] rust: auxiliary: validate DeviceId name length

[Georgios Androutsopoulos <georgeandrout13@gmail.com>]

`DeviceId::new()` copies `modname` and `name` into the fixed 40-byte
`auxiliary_device_id::name` array without checking that they fit. An
oversized name is caught by the array bounds check, but the error
reports an out-of-bounds index in the copy loop rather than the
constraint the caller violated.

Check the invariant explicitly instead, so the failure states the length
limit rather than an array index.

In a constant context exceeding the limit leads to a build error; at
runtime it panics, so add a `# Panics` section for it.

Fixes: ce735e73dd59 ("rust: auxiliary: add auxiliary device / driver abstractions")
Signed-off-by: Georgios Androutsopoulos <georgeandrout13@gmail.com>
---
 rust/kernel/auxiliary.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/rust/kernel/auxiliary.rs b/rust/kernel/auxiliary.rs
index 60dfbec8f330..1f3ba86d6d96 100644
--- a/rust/kernel/auxiliary.rs
+++ b/rust/kernel/auxiliary.rs
@@ -137,10 +137,20 @@ macro_rules! module_auxiliary_driver {
 
 impl DeviceId {
     /// Create a new [`DeviceId`] from name.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the combined module and device name, including the
+    /// separator and trailing NUL, exceeds `AUXILIARY_NAME_SIZE` bytes.
     pub const fn new(modname: &'static CStr, name: &'static CStr) -> Self {
         let name = name.to_bytes_with_nul();
         let modname = modname.to_bytes_with_nul();
 
+        assert!(
+            modname.len().saturating_add(name.len()) <= bindings::AUXILIARY_NAME_SIZE as usize,
+            "auxiliary device ID is too long"
+        );
+
         let mut id: bindings::auxiliary_device_id = pin_init::zeroed();
         let mut i = 0;
         while i < modname.len() {

base-commit: 28924df2a08f440c73991b83028032c901de2ae4
-- 
2.47.3