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Miller" , Jakub Kicinski , Petar Penkov , Eric Dumazet References: <20220124151146.376446-1-maximmi@nvidia.com> <20220124151146.376446-5-maximmi@nvidia.com> From: Maxim Mikityanskiy In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.126.230.35] X-ClientProxiedBy: drhqmail203.nvidia.com (10.126.190.182) To rnnvmail201.nvidia.com (10.129.68.8) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 6d1f3692-2bae-4c83-7b88-08d9e4bee57e X-MS-TrafficTypeDiagnostic: BN6PR1201MB2499:EE_ X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:8273; X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:12.22.5.234;CTRY:US;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:mail.nvidia.com;PTR:InfoNoRecords;CAT:NONE;SFS:(13230001)(4636009)(36840700001)(46966006)(40470700004)(86362001)(6916009)(508600001)(31696002)(70586007)(70206006)(54906003)(356005)(316002)(81166007)(16576012)(31686004)(36860700001)(4326008)(8936002)(8676002)(36756003)(26005)(16526019)(5660300002)(2616005)(2906002)(7416002)(6666004)(53546011)(47076005)(336012)(426003)(40460700003)(83380400001)(82310400004)(186003)(43740500002)(36900700001)(20210929001);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 31 Jan 2022 13:37:59.3108 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 6d1f3692-2bae-4c83-7b88-08d9e4bee57e X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[12.22.5.234];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT014.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN6PR1201MB2499 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2022-01-26 11:45, Lorenz Bauer wrote: > On Mon, 24 Jan 2022 at 15:13, Maxim Mikityanskiy wrote: >> >> bpf_tcp_gen_syncookie and bpf_tcp_check_syncookie expect the full length >> of the TCP header (with all extensions). Fix the documentation that says >> it should be sizeof(struct tcphdr). > > I don't understand this change, sorry. Are you referring to the fact > that the check is len < sizeof(*th) instead of len != sizeof(*th)? > > Your commit message makes me think that the helpers will access data > in the extension headers, which isn't true as far as I can tell. Yes, they will. See bpf_tcp_gen_syncookie -> tcp_v4_get_syncookie -> tcp_get_syncookie_mss -> tcp_parse_mss_option, which iterates over the TCP options ("extensions" wasn't the best word I used here). Moreover, bpf_tcp_gen_syncookie even checks that th_len == th->doff * 4. Although bpf_tcp_check_syncookie doesn't need the TCP options and doesn't enforce them to be passed, it's still allowed. > That > would be a problem in fact, since it could be used to read memory that > the verifier hasn't deemed safe. It's safe, because bpf_tcp_gen_syncookie reads up to th_len, which is ARG_CONST_SIZE for the TCP header.