linux-kernel - Re: [PATCH 1/3] rust: revocable: implement Revocable::access()

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: <aA0Vruu-rJWt146b@Mac.home>
Date: Sat, 26 Apr 2025 10:19:42 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Christian Schrefl <chrisi.schrefl@...il.com>,
	gregkh@...uxfoundation.org, rafael@...nel.org, bhelgaas@...gle.com,
	kwilczynski@...nel.org, zhiw@...dia.com, cjia@...dia.com,
	jhubbard@...dia.com, bskeggs@...dia.com, acurrid@...dia.com,
	joelagnelf@...dia.com, ttabi@...dia.com, acourbot@...dia.com,
	ojeda@...nel.org, alex.gaynor@...il.com, gary@...yguo.net,
	bjorn3_gh@...tonmail.com, benno.lossin@...ton.me,
	a.hindborg@...nel.org, aliceryhl@...gle.com, tmgross@...ch.edu,
	linux-pci@...r.kernel.org, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] rust: revocable: implement Revocable::access()

On Sat, Apr 26, 2025 at 07:01:52PM +0200, Danilo Krummrich wrote:
> On Sat, Apr 26, 2025 at 09:54:58AM -0700, Boqun Feng wrote:
> > On Sat, Apr 26, 2025 at 06:44:03PM +0200, Christian Schrefl wrote:
> > > On 26.04.25 3:30 PM, Danilo Krummrich wrote:
> > > > Implement an unsafe direct accessor for the data stored within the
> > > > Revocable.
> > > > 
> > > > This is useful for cases where we can proof that the data stored within
> > > > the Revocable is not and cannot be revoked for the duration of the
> > > > lifetime of the returned reference.
> > > > 
> > > > Signed-off-by: Danilo Krummrich <dakr@...nel.org>
> > > > ---
> > > > The explicit lifetimes in access() probably don't serve a practical
> > > > purpose, but I found them to be useful for documentation purposes.
> > > > --->  rust/kernel/revocable.rs | 12 ++++++++++++
> > > >  1 file changed, 12 insertions(+)
> > > > 
> > > > diff --git a/rust/kernel/revocable.rs b/rust/kernel/revocable.rs
> > > > index 971d0dc38d83..33535de141ce 100644
> > > > --- a/rust/kernel/revocable.rs
> > > > +++ b/rust/kernel/revocable.rs
> > > > @@ -139,6 +139,18 @@ pub fn try_access_with<R, F: FnOnce(&T) -> R>(&self, f: F) -> Option<R> {
> > > >          self.try_access().map(|t| f(&*t))
> > > >      }
> > > >  
> > > > +    /// Directly access the revocable wrapped object.
> > > > +    ///
> > > > +    /// # Safety
> > > > +    ///
> > > > +    /// The caller must ensure this [`Revocable`] instance hasn't been revoked and won't be revoked
> > > > +    /// for the duration of `'a`.
> > > > +    pub unsafe fn access<'a, 's: 'a>(&'s self) -> &'a T {
> > > I'm not sure if the `'s` lifetime really carries much meaning here.
> > > I find just (explicit) `'a` on both parameter and return value is clearer to me,
> > > but I'm not sure what others (particularly those not very familiar with rust)
> > > think of this.
> > 
> > Yeah, I don't think we need two lifetimes here, the following version
> > should be fine (with implicit lifetime):
> > 
> > 	pub unsafe fn access(&self) -> &T { ... }
> > 
> > , because if you do:
> > 
> > 	let revocable: &'1 Revocable = ...;
> > 	...
> > 	let t: &'2 T = unsafe { revocable.access() };
> > 
> > '1 should already outlive '2 (i.e. '1: '2).
> 
> Yes, this is indeed sufficient, that's why I wrote
> 
> 	"The explicit lifetimes in access() probably don't serve a practical
> 	purpose, but I found them to be useful for documentation purposes."
> 
> below the commit message. :)
> 

Sorry, I overlooked.

> Any opinions in terms of documentation purposes?
> 

I think for access() the explicit lifetimes is unnecessary, because it's
a one-lifetime case, the two explicit lifetimes would make a simple case
looking complicated.

For access_with(), that's needed and a good idea.

Just my two cents.

Regards,
Boqun

> > > 
> > > Either way:
> > > 
> > > Reviewed-by: Christian Schrefl <chrisi.schrefl@...il.com>
> > > 
> > > > +        // SAFETY: By the safety requirement of this function it is guaranteed that
> > > > +        // `self.data.get()` is a valid pointer to an instance of `T`.
> > > > +        unsafe { &*self.data.get() }
> > > > +    }
> > > > +
> > > >      /// # Safety
> > > >      ///
> > > >      /// Callers must ensure that there are no more concurrent users of the revocable object.
> > >