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Wysocki" , , Subject: Re: [PATCH v6 01/13] rust: auxiliary: let registration_data_with() closures return covariant sub-fields From: "Gary Guo" To: "Gary Guo" , "Alistair Popple" , , "nova-gpu" X-Mailer: aerc 0.22.0 References: <20260909064506.910162-1-apopple@nvidia.com> <20260909064506.910162-2-apopple@nvidia.com> In-Reply-To: X-ClientProxiedBy: LO4P123CA0436.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:1a9::9) To LOAP265MB8560.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:4ab::19) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LOAP265MB8560:EE_|CWLP265MB3138:EE_ X-MS-Office365-Filtering-Correlation-Id: 88f95707-a234-40a9-9215-08df2dfc5c42 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|10070799003|366016|1800799024|376014|7416014|4143699003|56012099006|10067099003|22082099003|18002099003; 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This prevents the >> closure from returning references derived from the registration data, >> even for sub-fields that are covariant in their lifetime, because the >> compiler cannot relate `'a` to any lifetime the caller knows about. >> >> Tie the outer reference to the `&self` lifetime instead, i.e. pass >> `Pin<&'this F::Of<'a>>`. This gives the closure the implied bound >> `'a: 'this`, so covariant sub-fields such as `&'a T` can be coerced to >> `'this` and returned directly, while invariant fields still cannot be >> coerced and therefore cannot escape with an incorrect lifetime. >> >> This allows auxiliary child drivers to project covariant data out of >> invariant registration data without having to wrap every use in a >> closure. > > Looking at this again I think the current API might be unsound where this= patch > becomes fix rather than just a feature update. > > For an invariant `&'b F::Of<'a>`, it's actually a requirement that `'a` s= trictly > outlive `'b`. With the current API surface, we can obtain a `&'a F::Of<'a= >`, > then we can store it inside `F::Of<'a>` (because, well, F::Of<'a> being > invariant, it can internally have a `Mutex>`), and then = we're > able to UAF within the destruction code of `F::Of<'a>`. > > The fix, is, well, this patch. > > Would you might pulling this patch out, rework the commit message a bit a= nd send > as a standalone fix? > > Best, > Gary Ah, I am looking at an old thread, this has been merged now. Ignore the message please. Best, Gary