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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?pIOeYhWpEz0V7jhPINX/E8yIntT7ppXJEJKgc9R4TSXEvBUjj+BffVGeFhco?= =?us-ascii?Q?AmjZdFNRR123VdFsIIXX+kWOR6HCMjTkaSmr30plD+ZZnqATlLODuAIXKT9M?= =?us-ascii?Q?m15zP7UlYFkF38c8aDtrnB4Y1LVxC8yP+nPVsGczsB3+xav6GN5eKGb113bC?= =?us-ascii?Q?6zxXsJeEzlTewxrkboy4Fx2YJEhyqXD4YNYGe5QSGcayKf2SQC99Z0jufaPd?= =?us-ascii?Q?1ABLkdbEjlNm0ubXeMoyKchyPT+KJv7gbuBAQ21lk1FED23e8X1TpIdo3Yjt?= =?us-ascii?Q?FSfLBeiGhnI3z1Y5rHGsJK7otyhUyeXBY7LuNsGz8DQEjDRl7zzP0t1BQtun?= =?us-ascii?Q?2zQ4ifbk0Qqup89DsZrq2l4eLGtQCptMnHFOMq15vyQCPbLz+/BiBwoZic64?= =?us-ascii?Q?Z7DGdScHvvNOkRlfPN36UQnjYQNI5mPqoEcFA4xYLGhuBUNW/Kj423wGU4Yr?= =?us-ascii?Q?A7podBjFd4a02SL9SwXl7UgKrw3r87Fo8mqT90zzAqEmwp5yMmHDlmZKkVZ1?= =?us-ascii?Q?Bx96e6x/TPzMloRFIL2xOQ3zoiux32q0z702uk45iv5TNx224GchAPgZlQ8U?= =?us-ascii?Q?dlOjH0UeHOq9LKVnKo46vatq2FXkeFkYk19xIAlk649BV2m0AEBatE7Yuw9a?= =?us-ascii?Q?MqnBX2kaAPGydqZN1WgDBrigEFY+BLGEwHeejpLMyTu+d8u3j4XlIIMRssCS?= =?us-ascii?Q?QTKCgj0t2BF1cMUM/zrQ8ib+XVoXL87IPXcgAkzgV67/XYRQFOa7S0gAYTuR?= =?us-ascii?Q?dYSLs3g+pdI9nFniSVUzYGeVAw+tdUftUz1BgekdzwMHXejOYb/LGTG+2RVg?= =?us-ascii?Q?LaoAsghUJWVwBDNl972XBxCs1+mb86UVuH8FMhZ24y2o3YInUfXZJ0XB/4EL?= =?us-ascii?Q?aVKI8VWEqralQtFcESxbeO/IBUUpaa9zu9ZZNg3Vc54Z9flvDzih0BFiOMe4?= =?us-ascii?Q?8KpH+AhkrIgIxr0mc7hFiFVkD2Xg8/EoqveZTM83VJlCjuZaBFkGlpdT0JMn?= =?us-ascii?Q?CPGW7AfmM+Gk1mUbAl0lfUUaz/QdZwOzBpV1kKurXIHUJlnDA+012l9IjeS2?= =?us-ascii?Q?n1ubJqdJw80rokbJfmfQwvtq0eeT8q60UjuevXEYJCLhhqU0cdZO1EXvgsIz?= =?us-ascii?Q?DuwjunZYzbz1QLBUa6EyozZjvV+5zVD1YD00O1DLGIVfZtAqHTBWxqaGIKMs?= =?us-ascii?Q?/ekp5WBFeoXzEI3XNFCgOumdiMk9ENaxt0PUVibU7yje8FS0QubwFI5zHTeY?= =?us-ascii?Q?ntaY4ZduP3F4WTkp103qW5uiFrA5KfiOsM2jgitnUii3FNity2cmP9F15sAQ?= =?us-ascii?Q?cW3Igg5LmodCcQaAxlMgviksSNJEs6gT7a/fD0KZ1HWOk/ZnPIAJlOyAWRKq?= =?us-ascii?Q?ZKMTNsnfniawUeeUYUG5LulubTuu4FQX8zzCtHKrUgNs8jgEd78WNm1RyX9B?= =?us-ascii?Q?/lJZaX8worDkVt6hXP9XvGnjSSAWLvz2zanv3Hkk/PbmNUFq3qeJ22uxf/lk?= =?us-ascii?Q?AjW8OyBhSqMmEj0b626laq77nsbLf4LMVHaPux4798P4mNTxZMh+h9iPD8dY?= =?us-ascii?Q?8l29e1DvQy+2x4E2AldPp6XshYBRSd4H6zklvirDp0V6kK6tLniWH2E5c7ms?= =?us-ascii?Q?sUg0n6vIMB2HpMGxgFmkODi8bfI6DUVwjMzWnsQN8Fc5er95gWhy43RLvL80?= =?us-ascii?Q?756UhI6jbjf+F9uq65NRgtpgzoOVH3GewDPy4YpdJP4MdmBQ?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 2efe7624-a7af-412a-6fb0-08df13ffc19a X-MS-Exchange-CrossTenant-AuthSource: PH0PR12MB7957.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 Sep 2026 14:35:29.6723 (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: rBflB4UrrhGPgTdPHjV0sphm2DfC2rq/OSFsFNu4yLXHSq3FOEisuyb+SohSYlw5BVRrZY0sCyMW+H7bo2S7EQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR12MB8017 On Wed, Sep 16, 2026 at 08:53:16PM +0800, Linkui Xiao wrote: > From: Linkui Xiao > > fib_select_multipath() compares nexthop_nh->nh_saddr against the flow > source address with no lock held, while fib_info_update_nhc_saddr() > stores a new value from another CPU as soon as the preferred source > address of the egress device changes. > > Commit 195374d89368 ("ipv4: fib: annotate races around nh->nh_saddr_genid > and nh->nh_saddr") added WRITE_ONCE() on the store side and READ_ONCE() > in fib_result_prefsrc() after syzbot reported > > BUG: KCSAN: data-race in fib_select_path / fib_select_path > > but it only covered that reader. fib_select_multipath(), reached from > fib_select_path(), is a second lockless reader of nh->nh_saddr and was > left bare. Nit (not worth a v4): This reads as if 195374d89368 missed fib_select_multipath(), but back then this function didn't use nh_saddr. > > Moreover, nh_saddr is only meaningful when nh_saddr_genid matches > dev_addr_genid, as established by commit 436c3b66ec98 ("ipv4: Invalidate > nexthop cache nh_saddr more correctly."). fib_select_multipath() > skips that validation, so it can score a nexthop using a stale source > address and skew the ECMP selection. > > Annotate both reads with READ_ONCE() and refresh the cached source > address via fib_info_update_nhc_saddr() when the genid does not match, > mirroring fib_result_prefsrc(). > > Fixes: 32607a332cfe ("ipv4: prefer multipath nexthop that matches source address") > Signed-off-by: Linkui Xiao Reviewed-by: Ido Schimmel