From: Danilo Krummrich <dakr@kernel.org>
Date: Thu, 16 Oct 2025 13:31:44 +0000 (+0200)
Subject: rust: device: fix device context of Device::parent()
X-Git-Tag: v6.17.6~105
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2b55b5be1d6cb0cd6f4e50e8a1b3590e366bc33d;p=thirdparty%2Fkernel%2Fstable.git

rust: device: fix device context of Device::parent()

commit cfec502b3d091ff7c24df6ccf8079470584315a0 upstream.

Regardless of the DeviceContext of a device, we can't give any
guarantees about the DeviceContext of its parent device.

This is very subtle, since it's only caused by a simple typo, i.e.

	 Self::from_raw(parent)

which preserves the DeviceContext in this case, vs.

	 Device::from_raw(parent)

which discards the DeviceContext.

(I should have noticed it doing the correct thing in auxiliary::Device
subsequently, but somehow missed it.)

Hence, fix both Device::parent() and auxiliary::Device::parent().

Cc: stable@vger.kernel.org
Fixes: a4c9f71e3440 ("rust: device: implement Device::parent()")
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/rust/kernel/auxiliary.rs b/rust/kernel/auxiliary.rs
index 4749fb6bffef3..3f7198e158ba1 100644
--- a/rust/kernel/auxiliary.rs
+++ b/rust/kernel/auxiliary.rs
@@ -217,13 +217,7 @@ impl<Ctx: device::DeviceContext> Device<Ctx> {
 
     /// Returns a reference to the parent [`device::Device`], if any.
     pub fn parent(&self) -> Option<&device::Device> {
-        let ptr: *const Self = self;
-        // CAST: `Device<Ctx: DeviceContext>` types are transparent to each other.
-        let ptr: *const Device = ptr.cast();
-        // SAFETY: `ptr` was derived from `&self`.
-        let this = unsafe { &*ptr };
-
-        this.as_ref().parent()
+        self.as_ref().parent()
     }
 }
 
diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
index a1db49eb159a3..e1a1c3e7f694e 100644
--- a/rust/kernel/device.rs
+++ b/rust/kernel/device.rs
@@ -250,7 +250,7 @@ impl<Ctx: DeviceContext> Device<Ctx> {
 
     /// Returns a reference to the parent device, if any.
     #[cfg_attr(not(CONFIG_AUXILIARY_BUS), expect(dead_code))]
-    pub(crate) fn parent(&self) -> Option<&Self> {
+    pub(crate) fn parent(&self) -> Option<&Device> {
         // SAFETY:
         // - By the type invariant `self.as_raw()` is always valid.
         // - The parent device is only ever set at device creation.
@@ -263,7 +263,7 @@ impl<Ctx: DeviceContext> Device<Ctx> {
             // - Since `parent` is not NULL, it must be a valid pointer to a `struct device`.
             // - `parent` is valid for the lifetime of `self`, since a `struct device` holds a
             //   reference count of its parent.
-            Some(unsafe { Self::from_raw(parent) })
+            Some(unsafe { Device::from_raw(parent) })
         }
     }