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Miller" , Jakub Kicinski , Paolo Abeni , David Ahern , Simon Horman , netdev@vger.kernel.org, eric.dumazet@gmail.com, TencentOS Corvus AI , Jun Yang , Fourie Zhang Subject: Re: [PATCH net] ipv6: sr: restore network header before routing and forwarding Message-ID: <20260830112118.GA2870495@shredder> References: <20260828141727.2372570-1-edumazet@google.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260828141727.2372570-1-edumazet@google.com> X-ClientProxiedBy: FR4P281CA0081.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:cd::14) To PH0PR12MB7957.namprd12.prod.outlook.com (2603:10b6:510:281::22) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH0PR12MB7957:EE_|SJ2PR12MB8158:EE_ X-MS-Office365-Filtering-Correlation-Id: 221a1ae6-425a-41db-c44e-08df0688d543 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|7416014|376014|23010399003|366016|10067099003|11063799006|5023799004|6133799003|3023799007|22082099003|18002099003|56012099006; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?kiLApCtE+uLMlMAKcetDYU/ZDKYvcW9/+hfdGyC/qlwhireMp+QwwzlHxRcB?= =?us-ascii?Q?Z9PUOhDEzZd5algWbsq+z3ppxT6Jo56JE8wdRXHE6PxZL1YSMSpkNz/nwfu7?= =?us-ascii?Q?xKYAC1U7ndohnT1+tXmB8lh8a9gX+Y+GRGcjtMK9TvTdXpFaa+TnwutD2/ap?= =?us-ascii?Q?9M5jY1S2e5yoeutXmXoEo/aekX6Vyrddi/DnjkO5L2kQFW+Cia5GeU/RBhKS?= =?us-ascii?Q?dbozOooQkJVWQnETbh9v1ndRXbUO6Fz8bsJ72HUlPYMyZxu33y3V8s3apR9h?= =?us-ascii?Q?PNBOPd7FQTxJ8xbgVUoE8snWjUfFIniw5FI1TuoSaqWEXj+xK6sQLltIvMVB?= =?us-ascii?Q?kNuNUTc2OhhM6F1J8At3VPUndEHtBJuKIPyKuZNRSev3Swyws5dVXEDozJO4?= =?us-ascii?Q?FDMF7+HOA5zO5eLU+NBum99Hijj9136TltVGki3XgAqSa9l7Hd5RF/LPibQN?= =?us-ascii?Q?jBFrU6W1VkotpprNJaZDPn7gbutG+ksM5AYOqFz1UAKtmprshQhUSHs5KnV0?= =?us-ascii?Q?f9nMvDYM5PifdlSqUva47ETbIlS+CID8Br2Bkx7HbB+2dlxDMDD7CHQFKMFI?= =?us-ascii?Q?1yNmNnuQGyqHX+pqS4To3l1EMNRMjftjfLtl0n2PtRUr5iuqhbBSLWeeo5gc?= =?us-ascii?Q?ibQ1V75F/249fwvJ3tyOgnW0AXYYIst1R/YW5/WtIWtx1rbY03q1E4nmXnBS?= =?us-ascii?Q?KFs1Wozd2olHdE3OP1wGpDXgs9MrLRMUiqpebcBk+fkMOe45kn3BR6NTMH2c?= =?us-ascii?Q?ayqwyt8tU8abfcyliKwPNQC1JRNHpyI6dRMNX/qgJF1sDF6nb7p1sWKNsikO?= =?us-ascii?Q?4Bjp7mf8OcFnWKujbnUKYOewPcurGkMaT94CAtB8QMOSgYeVBQrnM8o/aNpi?= =?us-ascii?Q?68EO/isvUryb77uwazjDaevaP1auMS/UM/pvfU3FD3zhOWFuHGx7zonH+FcF?= =?us-ascii?Q?psCNciWDj5jewT5TEjxKxRrxbsjPYAKRfrpq6kD5IOyuyHImrq0kqT0szObl?= =?us-ascii?Q?k41/Bx7QyhGzS5WfwteMSjgM9353vGRrzxgU5eKm6h+7GkyXxiei+Eq8BTvy?= =?us-ascii?Q?kQY4aVCoNK1qG8cYpJjEdlhnx/EBF0dLQNAT44kPDJWvBix7AVcYVw00gm8m?= =?us-ascii?Q?xK45PcAZxpjjEcESt0uHEq/ex4iZHWPxltWwXAlW9ugeE4NXAOeC8QXk2PWw?= =?us-ascii?Q?6ArMg1Q7FsjxNVRbmFYrdHx66TyiPM1KaTsMTfiWzbmwX1xEwrISym+IEfK3?= =?us-ascii?Q?cuysuAwUAp98Q7ZBe0MCPtgsij0WPa5mlM4SxUbCthfFlvcesbLZPj1X6Ewr?= =?us-ascii?Q?QGwdwrWCWUmV8FsQPncnHWHGmZTGWj6UMbRIAfHk4BeMt6mkbRZffl395N18?= =?us-ascii?Q?5aaDf336OFAadnFuikN85gypPO7hVot/2tTr8OTFrTdW3G2uDI6PamC+kWj1?= =?us-ascii?Q?0BWgOHIeVIC0V2p6a7Bt8lybmJWxnbzT8Gv/fPAtmJNcxwLzVu95CEdnXk5T?= =?us-ascii?Q?Zf7a1z0o5e6WACoTQfNHS5vi+IG/Sv22Azgi1wfrJmaNEI9EIrLkj3wkf2Iw?= =?us-ascii?Q?7G09HX+2jeGPcV1kFebV0Q9J2WfDhoCEQF4osCvMF61jH7L5FVArlnJ+RrFl?= =?us-ascii?Q?b8GRsG1ITAx1NqRMIPA3AN8nj42SbLW3dFE/ocqlWgtGa5AeZiYlDyYwcKJi?= =?us-ascii?Q?na7XEiqrQwSMG6pW+B+EI7qePwtYZ1ZFNmiRqdNPs2dUGkBx?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 221a1ae6-425a-41db-c44e-08df0688d543 X-MS-Exchange-CrossTenant-AuthSource: PH0PR12MB7957.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Aug 2026 11:21:27.4366 (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: lghNglB5JI1ps0h8AO1uHKm1fToLTzI8GneeYwQkC4YfmycFwFITbi56owZzNAvYqaMCBmNacAPN94MNNXxRgw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ2PR12MB8158 On Fri, Aug 28, 2026 at 02:17:27PM +0000, Eric Dumazet wrote: > ipv6_srh_rcv() runs with skb->data at the Segment Routing Header (SRH) > while skb_network_header() points at the IPv6 header. > > When segments_left > 0, ipv6_srh_rcv() previously restored the skb->data > position by pushing sizeof(struct ipv6hdr), assuming the SRH immediately > followed the fixed IPv6 header. If another extension header (such as a > Hop-by-Hop options header) precedes the SRH, skb_network_offset() > remained negative. > > This led to two problems: > 1. During ip6_route_input(), fib6_rules_early_flow_dissect() invokes > __skb_flow_dissect() which passes the negative skb_network_offset() > to flow dissection, breaking BPF and C flow dissector logic. > 2. If forwarded via ip6_forward() or redirected via act_mirred, downstream > handlers (like sch_fragment() or neighbour output) pass the negative > offset as an unsigned length, triggering OOB memcpy or buffer overflows. > > Fix this by pushing -skb_network_offset(skb) before routing, ensuring > skb_network_offset(skb) is 0 for route lookup / flow dissection as well as > downstream forwarding. On the loopback path, pull skb_transport_offset(skb) > to restore skb->data to the SRH before looping back. > > Fixes: 1ababeba4a21 ("ipv6: implement dataplane support for rthdr type 4 (Segment Routing Header)") > Reported-by: TencentOS Corvus AI > Reported-by: Jun Yang > Reported-by: Fourie Zhang > Closes: https://lore.kernel.org/netdev/20260817104128.22681-1-juny24602@gmail.com/ > Closes: https://lore.kernel.org/netdev/20260827092345.2301937-1-fouriezhang@tencent.com/ > Signed-off-by: Eric Dumazet Reviewed-by: Ido Schimmel