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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?dqwik05npJE3FScxL7YTACy9uBx4dTH23roA0EGrH8091ohZbzQSRDJG1eXr?= =?us-ascii?Q?6CVVV7J/ao4iztk3Ahh1WoAc0dKy67eeS9HlGvsoUa1YDmHNGkk6LJAD3wFJ?= =?us-ascii?Q?hSxRhtShq1tQcp6yjX3BFn9hcFG5EDQRp12IDevfKxetfPYTaMBR8ppOd5Fw?= =?us-ascii?Q?ad140+ADNbgL6aqmwhOm4zEbb91JLrfDBJQB4xttHUv5MPLREgjb2CGMjoMo?= =?us-ascii?Q?uc6Ixal3KiV52jZLfJoM+OdJ4q/s71OF+HJVHin5W/ufsw5/t28nwfYyOeXG?= =?us-ascii?Q?iQMQgjVPQnNzR4cIjFTnucgvoYRRoCINsLltgwroJPQCChxhV9X2jnSQoImd?= =?us-ascii?Q?38vHpgYWZAwASyzqta+jSUkKeRgIlwA8tboN134Ht2ruKdyTMe9QFMVuZg6l?= =?us-ascii?Q?T5tWajgVskgQZ8YM0svcPWKY0ZKMjuFS5WQNNr2wK5js9jWoE4P7hY9qgg7Y?= =?us-ascii?Q?a5/ElAh0zwQ+lPM3O39DQUim5TWTd6TSpXV6hW61C5ynVrt5xNw4LcOk9Ulz?= =?us-ascii?Q?Mb8X0JgVn+ApbUIaU9GaujJtrS5ccgoS5Ix8yuOC/xkdXCHGnE5wsbvVsgTT?= =?us-ascii?Q?e9tsDThJwEbnzu3DmxJc+McOIyVPoC5blbh3GGyiH5n2SMbEyzCLTQVHygbm?= =?us-ascii?Q?VBA87t47kkzefr/T+UYPAQG9qKB2JED3tc+DCZE+Hq7ly+Y+EYVNqXOck6pL?= =?us-ascii?Q?XoDpkZ484dmOIN7to1bNSr97HeFmaCf7IZ9jpoC7ukmTIJtSE/QfJ+N4z1Ul?= =?us-ascii?Q?biernx8+B3ttv6EJsEAqZQCaCKAV4OgUA+qIUYA79RVGyeXOZ8AIB6kYISLZ?= =?us-ascii?Q?3ahlVXO1in6E0j43yMXgpxiXf+Mq3J7E+nPULaTcLalsHL7gfEOyggBSZ++j?= =?us-ascii?Q?mRWd17j2sEk8NPHnuRkExDX8jLMvA2xddHsH3tZu5CuFvIVpKsiEU10yCKe1?= =?us-ascii?Q?xMZPX12y29GSXwW2oXs3ZjKNo4Lf2SnqTICy/5jFba57ElGNryTl+J2RXRJ+?= =?us-ascii?Q?KRa8KNc7DMmYI2HcjGffAnpprv1BYhanqIjVE9jXMsDxpyombkFY1wZjjlzd?= =?us-ascii?Q?UB1YBvwCin7KgB/qns/LktLIrxEVwxtqNR++qQIv9Es+Y2ZK5UJreAsYc/TE?= =?us-ascii?Q?gNhniXiQzgKhfY0h8uNWLq3vV6diFQPdgchH7PlKK+ZEDUQszfxHXNjHKr3E?= =?us-ascii?Q?5wmLBzJJh4eB/W5OhQstQDnI/nlVZq1XSfeuebi3KfWLwPZ9qqYRqieEiCJO?= =?us-ascii?Q?snBV3VCOUoTLmvKylX1h7LnSDvnsqlKGYFzP4eJjFgaZbVTMbFnWwvhThMIK?= =?us-ascii?Q?sZKgo6txaZDxuvuWZiCVBjalmeNEY5iwFE7UNggJVaLaYxthD4gRoEodE0kW?= =?us-ascii?Q?IoEvd27+pcLpKjrtsiV78B/d0e78ERTTrK9pFpjH20K+ojekfAByaMBN+OcN?= =?us-ascii?Q?Ne8SoS7Eh0Crz/lcqBram5LcxztQOqZmxu/bMJMILoRdqgqlAqxkPMF3AzQT?= =?us-ascii?Q?0j8hrP+yg1BssXZ+qT5XpCR9+jfV8bS/SziRO4kQTjSKkYAxbQLVlgRhrlgK?= =?us-ascii?Q?jL6YWy6rIeMVIozukdmoiAGADv6Lt6qdB+KK/BGpwBlCnjxo2ZpzxjuCQx5d?= =?us-ascii?Q?Qxj2bnsKwa1gDBXKP7iRRihitCTjWuDCXVHK25FHsBR5IlL4+dy/YKvsvcds?= =?us-ascii?Q?LXTY2lZJA1CJnXrJed2B+tijfZxgJKgjXIEFIow3nNphA80O?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: f1b496ea-2c9e-4bfe-5e1d-08def5e58bc6 X-MS-Exchange-CrossTenant-AuthSource: SA3PR12MB7901.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Aug 2026 07:12:17.5785 (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: 6aqRm3vmUeW4muflIAvi3mdLkvf3palcLVHFWfeRTxT5J3BazxjuXXmFh7BU5onemorWQ1inQAV3pn4H/noxPw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA0PR12MB8253 On Sat, Aug 08, 2026 at 02:17:10AM +0800, Chengfeng Ye wrote: > fib_nhc_update_mtu() walks the nexthop exception table under RTNL, but > RTNL does not serialize this walk with PMTU exception updates. The walk > uses rcu_dereference_protected() with a constant true condition without > holding fnhe_lock. > > The following interleaving can therefore occur: > > CPU 0 CPU 1 > fib_nhc_update_mtu() update_or_create_fnhe() > load fnhe spin_lock_bh(&fnhe_lock) > fnhe_remove_oldest() > unlink fnhe > kfree_rcu(fnhe, rcu) > > access fnhe after grace period > > KASAN reported: > > BUG: KASAN: slab-use-after-free in fib_nhc_update_mtu+0x3df/0x410 > Read of size 8 at addr ffff888107d49000 by task poc/90 > Call Trace: > fib_nhc_update_mtu+0x3df/0x410 > fib_sync_mtu+0x7a/0xd0 > fib_netdev_event+0x229/0x3f0 > netif_set_mtu_ext+0x33a/0x570 > dev_set_mtu+0x88/0x120 > > The same walk updates fnhe_pmtu and fnhe_mtu_locked. These fields form a > pair and other writers serialize them with fnhe_lock. RCU alone prevents > reclamation, but would still allow concurrent writers to leave a mixed > pair. > > Walk the table under RCU and acquire fnhe_lock only while updating each > exception. RCU keeps the current entry alive while the short critical > section serializes its paired PMTU fields. This avoids holding the global > lock while scanning all 2048 buckets for every nexthop. > > Fixes: af7d6cce5369 ("net: ipv4: update fnhe_pmtu when first hop's MTU changes") > Cc: stable@vger.kernel.org > Suggested-by: Ido Schimmel > Signed-off-by: Chengfeng Ye Reviewed-by: Ido Schimmel