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Wysocki" , Danilo Krummrich , Jonathan Corbet , Shuah Khan , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, chrome-platform@lists.linux.dev, linux-kselftest@vger.kernel.org, Laurent Pinchart , Bartosz Golaszewski , Wolfram Sang , Simona Vetter , Dan Williams Subject: Re: [PATCH v6 1/3] revocable: Add fops replacement Message-ID: <20251107141509.GK1732817@nvidia.com> References: <20251106152712.11850-1-tzungbi@kernel.org> <20251106152712.11850-2-tzungbi@kernel.org> <20251106154715.GB1732817@nvidia.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: MN2PR06CA0017.namprd06.prod.outlook.com (2603:10b6:208:23d::22) To MN2PR12MB3613.namprd12.prod.outlook.com (2603:10b6:208:c1::17) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MN2PR12MB3613:EE_|SA3PR12MB9108:EE_ X-MS-Office365-Filtering-Correlation-Id: a4ef0919-4a17-4289-3f18-08de1e080f91 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|7416014|1800799024; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?BMtTh8aFhWIN9+bVTMFJNMHenqGrikynu17UNGgyjc12iPO3L77031xII0jy?= =?us-ascii?Q?TiqEcjbXWxy219m9a4hsaJtX8HHzVX+fhRFLDTihqjtFQG2Ez+9KJofUSl+L?= =?us-ascii?Q?4reYR9/89exzfBdamBvWj39pDwos8imiUgCt12p5291oKdoGGSTw6y162BIP?= =?us-ascii?Q?YKxHUaw1AxA7PjbU9fnXiQeH1fKNWXr55obtZlk0jK8fXwBcUqf95McicIFg?= =?us-ascii?Q?yNFv8A7CTgRzirqu6tT1nok7y0FG3rVcXH7itZGoJ3k0MoVbZM000BmyjKcp?= =?us-ascii?Q?1nALm6vZdhNDfAjoskpktch6E7Et3JqdqvNTHHLIIE76BomgfkM8S2Jr98Bt?= =?us-ascii?Q?Nvw67+XaPe5QexMls71A9mWF91fL+7MR5Q8MvTGEwSQbPA7F1BVQ22hT9rxd?= =?us-ascii?Q?s256Bh+HIKCAXXXYYepqhDlQqJzP3U1Lwl3XzrcmaW0lUmPbRPSLu5m8lKHA?= =?us-ascii?Q?DjkLkLsaLQlARQ1fq7ITSUUwoAiFRzgKa6gjSJnPNxbwPT/E0IUyjetty8m8?= =?us-ascii?Q?NoCS2bW/jrCEgebsG/0oJqNytQyC+e7PuLImG7sQXFAdY6ruFFdZ6zAUECcC?= =?us-ascii?Q?OY2lDTWmOq5Nu4YzJZidFjdXcPRTuCPm82k/IcNOi7IpxuS+7g3FpnQfV3Qk?= =?us-ascii?Q?kx6/fLkCBjFol9CKfLqY6kgPe5GS5CkbjbtFUWWIyCHYjIxE9Yt/29kqhlIG?= =?us-ascii?Q?fsamkqMBx7wRMjZFQiYSuvzrtXEXpYcC4IvVrbiayMsSlO8QGs0S6YwD5Ubq?= =?us-ascii?Q?Fo/pRAttH3oaVYzD7aMOhL4y+7z6Fpb/J1xiHDIaGpEZMVmokrKWMlc5ygPG?= =?us-ascii?Q?c9zFf73zdYEdsp3zrdzTIKMdkrBxSvE/BnwejdNNQ8qN3xooiLOK0tsul8k8?= =?us-ascii?Q?Fc8tm/7QJzOzjlQz/NcercmGjAxeCVwOZeY2OUOA1iaHq2IcCvJywlo9Ejqh?= =?us-ascii?Q?RKWaG0QwwSEmMZBnlSnPZ7ffBMNhOayvR7ky2+4bMAg8jqkVUYSz+L2+kS/f?= =?us-ascii?Q?NDJDYRQQxD/C3ZjA0DZWGi/XUKDGOUe3bMf5AvXE2Cn5/2VVPgVfNBwyiKeh?= =?us-ascii?Q?7Kt0OZC60Fx+BaTXAtFUun99aaeflHbm4QjQx2je1Hih/z2vBOHng1s+JkPp?= =?us-ascii?Q?cJiXOrrE1+QXEVr3HrHqKDJyA6LPQC+CSuUzOWHC27DqeRPHrqETwpIQ2p18?= =?us-ascii?Q?Rm0SYHiAWyqDC8p+/i2gsjfRj8pTyt91IF7NbjPYG32CGHxIUtzMaYS7bXdw?= =?us-ascii?Q?GC/3Pwk7kV/NY10Qa6C8k7Uvr4rEtxUAbTZsDxGIujIwRfysBsLawPwLvcSO?= =?us-ascii?Q?mVngolLoZQ2obINbFc1PgJ3zLd4Wlbvj5XCcinMCnb9PobXqGd4GbrA34jLa?= =?us-ascii?Q?qDmncCNpiE3jTQrB5mt4WMdy5DN9ah1SLzUxGrfcKFz/BiPEohgWzP4HUt/L?= =?us-ascii?Q?6wjFhW5xyAr/zzL27Fn9sDNOrnGusZvQXj/q0O1tPpDag9laEnutRUU9Mb+B?= =?us-ascii?Q?r9UcVtfC1+cqzKRRb2rXiShIU3ev8CdI7YKnH5185XHY7+vJYWF/KsQJ5R2h?= =?us-ascii?Q?5zKcnQBApsaPp8z7b1I=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: a4ef0919-4a17-4289-3f18-08de1e080f91 X-MS-Exchange-CrossTenant-AuthSource: MN2PR12MB3613.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Nov 2025 14:15:10.4306 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 4rG8DqM6de70l3y8/5N0WNsHBf5/DYSsjj0rvho0VMKVUKH4WEfb9GdSYYiXOYKy X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA3PR12MB9108 On Fri, Nov 07, 2025 at 05:07:54AM +0000, Tzung-Bi Shih wrote: > On Thu, Nov 06, 2025 at 11:47:15AM -0400, Jason Gunthorpe wrote: > > On Thu, Nov 06, 2025 at 11:27:10PM +0800, Tzung-Bi Shih wrote: > > > +/* > > > + * Recover the private_data to its original one. > > > + */ > > > +static struct fops_replacement *_recover_private_data(struct file *filp) > > > +{ > > > + struct fops_replacement *fr = filp->private_data; > > > + > > > + filp->private_data = fr->orig_private_data; > > > + return fr; > > > +} > > > + > > > +/* > > > + * Replace the private_data to fops_replacement. > > > + */ > > > +static void _replace_private_data(struct fops_replacement *fr) > > > +{ > > > + fr->filp->private_data = fr; > > > +} > > > > This switching of private_data isn't reasonable, it breaks too much > > stuff. I think I showed a better idea in my sketch. > > The approach assumes the filp->private_data should be set once by the > filp->f_op->open() if any. Is it common that the filp->private_data > be updated in other file operations? You can set it once during open, but you can't change it around every fops callback. This stuff is all concurrent. > > This probably doesn't work out, is likely to make a memory leak. > > It will be hard for the owning driver to free its per-file memory > > without access to release. > > Ah, I think this reveals a drawback of the approach. > - Without calling ->release(), some memory may leak. > - With calling ->release(), some UAF may happen. It just means the user of this needs to understand there are limitations on what release can do. Usually release just frees memory, that is fine. I think it would be strange for a release to touch revocable data, that might suggest some larger problem. Jason