rust: regulator: do not assume that regulator_get() returns non-null

The Rust `Regulator` abstraction uses `NonNull` to wrap the underlying
`struct regulator` pointer. When `CONFIG_REGULATOR` is disabled, the C
stub for `regulator_get` returns `NULL`. `from_err_ptr` does not treat
`NULL` as an error, so it was passed to `NonNull::new_unchecked`,
causing undefined behavior.

Fix this by using a raw pointer `*mut bindings::regulator` instead of
`NonNull`. This allows `inner` to be `NULL` when `CONFIG_REGULATOR` is
disabled, and leverages the C stubs which are designed to handle `NULL`
or are no-ops.

Fixes: 9b614ceada ("rust: regulator: add a bare minimum regulator abstraction")
Reported-by: Miguel Ojeda <ojeda@kernel.org>
Closes: https://lore.kernel.org/r/20260322193830.89324-1-ojeda@kernel.org
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Link: https://patch.msgid.link/20260324-regulator-fix-v1-1-a5244afa3c15@google.com
Signed-off-by: Mark Brown <broonie@kernel.org>

rust/kernel/regulator.rs

@@ -23,7 +23,10 @@ use crate::{
     prelude::*,
 };
 
-use core::{marker::PhantomData, mem::ManuallyDrop, ptr::NonNull};
+use core::{
+    marker::PhantomData,
+    mem::ManuallyDrop, //
+};
 
 mod private {
     pub trait Sealed {}
@@ -229,15 +232,17 @@ pub fn devm_enable_optional(dev: &Device<Bound>, name: &CStr) -> Result {
 ///
 /// # Invariants
 ///
-/// - `inner` is a non-null wrapper over a pointer to a `struct
-///   regulator` obtained from [`regulator_get()`].
+/// - `inner` is a pointer obtained from a successful call to
+///   [`regulator_get()`]. It is treated as an opaque token that may only be
+///   accessed using C API methods (e.g., it may be `NULL` if the C API returns
+///   `NULL`).
 ///
 /// [`regulator_get()`]: https://docs.kernel.org/driver-api/regulator.html#c.regulator_get
 pub struct Regulator<State>
 where
     State: RegulatorState,
 {
-    inner: NonNull<bindings::regulator>,
+    inner: *mut bindings::regulator,
     _phantom: PhantomData<State>,
 }
 
@@ -249,7 +254,7 @@ impl<T: RegulatorState> Regulator<T> {
         // SAFETY: Safe as per the type invariants of `Regulator`.
         to_result(unsafe {
             bindings::regulator_set_voltage(
-                self.inner.as_ptr(),
+                self.inner,
                 min_voltage.as_microvolts(),
                 max_voltage.as_microvolts(),
             )
@@ -259,7 +264,7 @@ impl<T: RegulatorState> Regulator<T> {
     /// Gets the current voltage of the regulator.
     pub fn get_voltage(&self) -> Result<Voltage> {
         // SAFETY: Safe as per the type invariants of `Regulator`.
-        let voltage = unsafe { bindings::regulator_get_voltage(self.inner.as_ptr()) };
+        let voltage = unsafe { bindings::regulator_get_voltage(self.inner) };
 
         to_result(voltage).map(|()| Voltage::from_microvolts(voltage))
     }
@@ -270,10 +275,8 @@ impl<T: RegulatorState> Regulator<T> {
             // received from the C code.
             from_err_ptr(unsafe { bindings::regulator_get(dev.as_raw(), name.as_char_ptr()) })?;
 
-        // SAFETY: We can safely trust `inner` to be a pointer to a valid
-        // regulator if `ERR_PTR` was not returned.
-        let inner = unsafe { NonNull::new_unchecked(inner) };
-
+        // INVARIANT: `inner` is a pointer obtained from `regulator_get()`, and
+        // the call was successful.
         Ok(Self {
             inner,
             _phantom: PhantomData,
@@ -282,12 +285,12 @@ impl<T: RegulatorState> Regulator<T> {
 
     fn enable_internal(&self) -> Result {
         // SAFETY: Safe as per the type invariants of `Regulator`.
-        to_result(unsafe { bindings::regulator_enable(self.inner.as_ptr()) })
+        to_result(unsafe { bindings::regulator_enable(self.inner) })
     }
 
     fn disable_internal(&self) -> Result {
         // SAFETY: Safe as per the type invariants of `Regulator`.
-        to_result(unsafe { bindings::regulator_disable(self.inner.as_ptr()) })
+        to_result(unsafe { bindings::regulator_disable(self.inner) })
     }
 }
 
@@ -349,7 +352,7 @@ impl<T: IsEnabled> Regulator<T> {
     /// Checks if the regulator is enabled.
     pub fn is_enabled(&self) -> bool {
         // SAFETY: Safe as per the type invariants of `Regulator`.
-        unsafe { bindings::regulator_is_enabled(self.inner.as_ptr()) != 0 }
+        unsafe { bindings::regulator_is_enabled(self.inner) != 0 }
     }
 }
 
@@ -359,11 +362,11 @@ impl<T: RegulatorState> Drop for Regulator<T> {
             // SAFETY: By the type invariants, we know that `self` owns a
             // reference on the enabled refcount, so it is safe to relinquish it
             // now.
-            unsafe { bindings::regulator_disable(self.inner.as_ptr()) };
+            unsafe { bindings::regulator_disable(self.inner) };
         }
         // SAFETY: By the type invariants, we know that `self` owns a reference,
         // so it is safe to relinquish it now.
-        unsafe { bindings::regulator_put(self.inner.as_ptr()) };
+        unsafe { bindings::regulator_put(self.inner) };
     }
 }