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charset=UTF-8 Date: Tue, 25 Aug 2026 00:27:44 +0900 Message-Id: Cc: , "Yury Norov" , "Miguel Ojeda" , "Boqun Feng" , "Gary Guo" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Andreas Hindborg" , "Alice Ryhl" , "Trevor Gross" , "Danilo Krummrich" , "Daniel Almeida" , "Tamir Duberstein" , =?utf-8?q?Onur_=C3=96zkan?= , , , Subject: Re: [PATCH v4] rust: num: restrict bool conversion to unsigned Bounded From: "Alexandre Courbot" To: "Miguel Ojeda" References: <20260822-fix-rust-bounded-from-bool-submit-v4-1-aa780bfe7f30@younes.io> In-Reply-To: X-ClientProxiedBy: TY4P286CA0091.JPNP286.PROD.OUTLOOK.COM (2603:1096:405:369::10) To MW4PR12MB6873.namprd12.prod.outlook.com (2603:10b6:303:20c::17) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MW4PR12MB6873:EE_|SJ5PPFB332093D3:EE_ X-MS-Office365-Filtering-Correlation-Id: 8c77d0d7-e9fe-48c3-512e-08df01f4402b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|10070799003|7416014|376014|23010399003|1800799024|6133799003|10067099003|4143699003|11063799006|56012099006|18002099003|22082099003; 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A signed Bounded with N =3D 1 can hold >> only -1 and 0. The current implementation can therefore create a value >> that breaks Bounded's invariant. Deref relies on that invariant and >> calls unreachable_unchecked() when it is broken, so safe Rust can reach >> undefined behavior. >> >> The other primitive conversions require the source and destination to >> have the same signedness. Treat bool as an unsigned one-bit value and >> allow conversions between bool and Bounded only when the backing integer >> type is unsigned. >> >> Fixes: 01e345e82ec3 ("rust: num: add Bounded integer wrapping type") >> Closes: https://lore.kernel.org/rust-for-linux/OzuVxu0--J-9@younes.io/ >> Cc: stable@vger.kernel.org >> Suggested-by: Alexandre Courbot >> Assisted-by: Codex:gpt-5.6-sol >> Signed-off-by: Younes Akhouayri > > Applied to `rust-fixes` -- thanks everyone! > > Reviewing this with an LLM made me notice that we should probably seal > `Integer` or make it `unsafe`, because currently someone can > buggily/maliciously implement it to still trigger UB regardless of > this fix. Good idea indeed. I'll send a patch to seal it, thanks for mentioning it!