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Wed, 18 Mar 2026 07:22:15 +0000 From: Dan Williams Date: Wed, 18 Mar 2026 00:22:13 -0700 To: Lukas Wunner , Dan Williams CC: , , , , , , , , , Donald Hunter , Jakub Kicinski Message-ID: <69ba52a590255_7ee310050@dwillia2-mobl4.notmuch> In-Reply-To: References: <20260303000207.1836586-1-dan.j.williams@intel.com> <20260303000207.1836586-9-dan.j.williams@intel.com> <69b8646c8aeb1_452b100aa@dwillia2-mobl4.notmuch> <69b88bfe2662f_40c01002c@dwillia2-mobl4.notmuch> Subject: Re: [PATCH v2 08/19] PCI/TSM: Add "evidence" support Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR05CA0080.namprd05.prod.outlook.com (2603:10b6:a03:e0::21) To PH8PR11MB8107.namprd11.prod.outlook.com (2603:10b6:510:256::6) Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH8PR11MB8107:EE_|DM4PR11MB7351:EE_ X-MS-Office365-Filtering-Correlation-Id: e7e622b8-d7bf-45ac-332b-08de84bf14d9 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|7416014|376014|366016|18002099003|56012099003|22082099003; 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A given attribute in this > > implementation never exceeds the limit > > Famous last words. I am not convinced you have found the "gotcha" you think you have... > If you look at netlink_dump(), it sizes the skb based on > nlk->max_recvmsg_len. If that's larger than 64k, you'll > try to fill as much as possible of that space with a single > netlink attribute. The computation of "available" in your > patch doesn't take the 65531 bytes limit for a netlink attribute > into account so it looks like you'll end up overflowing the length > of the netlink attribute. The @len to nla_put() should not overflow because it is based on the available tailroom in the skb minus netlink overhead. The "inventive" hack that Jakub is reacting to is that this scheme requires a receiver that assumes repeating the attribute in the receive stream must be handled as concatenation. > Unfortunately nla_put() doesn't prevent such overflows, it does > all the size calculations with an int, not a u16. Are we looking at the same capacity calculation? len = min(available - overhead, object_len - ctx->offset);