linux-kernel - Re: [PATCH v6 4/9] rust: device: Enable printing fwnode name and path

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aDMRkq9oPzFJBBzy@pollux.localdomain>
Date: Sun, 25 May 2025 14:48:18 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Remo Senekowitsch <remo@...nzli.dev>
Cc: Rob Herring <robh@...nel.org>, Saravana Kannan <saravanak@...gle.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <lossin@...nel.org>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Dirk Behme <dirk.behme@...bosch.com>, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v6 4/9] rust: device: Enable printing fwnode name and path

On Sat, May 24, 2025 at 09:22:27PM +0200, Remo Senekowitsch wrote:
> +    /// Returns an object that implements [`Display`](core::fmt::Display) for
> +    /// printing the full path of a node.
> +    pub fn display_path(&self) -> impl core::fmt::Display + '_ {

While testing the code I found the following buggy print statement:

	"test-device@...est-device@...est-device@...est-device@2: property 'test,u32-required-prop' is missing"

and I think the following changes fix this:

> +        struct FwNodeDisplayPath<'a>(&'a FwNode);
> +
> +        impl core::fmt::Display for FwNodeDisplayPath<'_> {
> +            fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
> +                // The logic here is the same as the one in lib/vsprintf.c
> +                // (fwnode_full_name_string).
> +
> +                // SAFETY: `self.0.as_raw()` is valid by its type invariant.
> +                let num_parents = unsafe { bindings::fwnode_count_parents(self.0.as_raw()) };
> +
> +                for depth in (0..=num_parents).rev() {
> +                    let fwnode = if depth == 0 {
> +                        self.0.as_raw()

	self.0

> +                    } else {
> +                        // SAFETY: `self.0.as_raw()` is valid.
> +                        unsafe { bindings::fwnode_get_nth_parent(self.0.as_raw(), depth) }

	let ptr = unsafe { bindings::fwnode_get_nth_parent(self.0.as_raw(), depth) };
	FwNode::as_ref(ptr)

where FwNode::as_ref() is

	unsafe fn as_ref<'a>(ptr: *mut bindings::fwnode_handle) -> &'a Self

> +                    };
> +
> +                    // SAFETY: `fwnode` is valid, it is either `self.0.as_raw()`
> +                    // or the return value of `bindings::fwnode_get_nth_parent`
> +                    // which returns a valid pointer to a `fwnode_handle` if the
> +                    // provided depth is within the valid range, which we know
> +                    // to be true.
> +                    let prefix = unsafe { bindings::fwnode_get_name_prefix(fwnode) };
> +                    if !prefix.is_null() {
> +                        // SAFETY: `fwnode_get_name_prefix` returns null or a
> +                        // valid C string.
> +                        let prefix = unsafe { CStr::from_char_ptr(prefix) };
> +                        write!(f, "{prefix}")?;
> +                    }
> +                    write!(f, "{}", self.0.display_name())?;

	write!(f, "{}", fwnode.0.display_name())?;

Otherwise we always write the name of self, no matter the actual parent depth.

> +
> +                    if depth != 0 {
> +                        // SAFETY:
> +                        // - `fwnode` is valid, because `depth` is
> +                        //   a valid depth of a parent of `self.0.as_raw()`.
> +                        // - `fwnode_get_nth_parent` increments the refcount and
> +                        //   we are responsible to decrement it.
> +                        unsafe { bindings::fwnode_handle_put(fwnode) }
> +                    }
> +                }
> +
> +                Ok(())
> +            }
> +        }
> +
> +        FwNodeDisplayPath(self)
> +    }