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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?g9J49EHWFMZCTC+VX7NeqD74zc0QxReqNgK5Fl9vlu+wb9GSoIXhYifFNvzs?= =?us-ascii?Q?1N9xX2C+EJxqtSh48aG2Z8D3dnDNVB/XrEloFWzyumxhdWLSxcjLZdwNuYQ6?= =?us-ascii?Q?4PSLcpS7VFQXJqtqa8TGJdoxfwHVTwY6C1JcALzTNF7Mv0Y2/+yEs8067WjV?= =?us-ascii?Q?8q42zwKZjB48tTPC9t9WvdmWVo6o0PrUnxBHBdQBG6Bkj7lL+YH8w7h8GgTr?= =?us-ascii?Q?ZjsDvfJeAzy/5/6clu1En28E7LV31d9njkMahSPloOKFWXQ9GckP072ik9Mq?= =?us-ascii?Q?CIZhlYG/Lzi7nIAt9IQSdxPoSLN5Tc4U60B2QyuUFDS9FeZHjtvaeEg8q6Qo?= =?us-ascii?Q?Zg+K5sMdbr8YSKZGthkZn7DoLHKUUahlzWM1OGZzJfJQbSBkiVyIhi6p2+1Q?= =?us-ascii?Q?n+mAgYyrFiS400c/qcT6z2TT1uoUoS7S6Gbn6EcKWPmDTMceynReXAv2RYyj?= =?us-ascii?Q?G1Fe7duMT9fYSD7EZmi2WdE6LXfuUZWVObgjCWyjtFzfmjWYZS93fivRzyMm?= =?us-ascii?Q?Llx8E3NcgKdXPTA50WZP/VQ2/oRdMtUD+ls0XkI9MvAmxMFJYlLrpajHFX7S?= =?us-ascii?Q?pXuMPVvoYEliQ6Xq0jpo7zYAnRgVzMNGa6eQtorfaEbEM7vCwMjFNIjUK13c?= =?us-ascii?Q?7Kml1wcDZuNAXSBDTYGdgFlsvH613vHq6OoBYxlQqW7ZNnURpOmEuV3jmErp?= =?us-ascii?Q?8phRfBg6kXOyVo6YHt4E09S/02MEHdGZ9fI0qrPaKnGbitk8EbIK+eBck+Rd?= =?us-ascii?Q?4JDavbX1k7va/1GSMsWZ2kreXM2qeo11iAzp1tRZXlBEvc9zgwGkT8Id44oK?= =?us-ascii?Q?929cjbMrsTUdTVOqBSdo33uqAhQJp09DaKKQDVT6FFfp8jy13IyVVBj73xcz?= =?us-ascii?Q?vePRi+AMw2/V0Xz1xr22ZrtRpD4X01EC1mp2Q8DddnkgmgZGg5jSi5rAP666?= =?us-ascii?Q?/byS2/drwZglUZfZ/GdgQYVbesYJzp4tPYzvU2BpY0oo25qeBBkAxPVfX0A8?= =?us-ascii?Q?/2lP9UfG+qwIdah4ZrKVflinPKua4d4r8dU9pjAlAhOGA5AmkhIIxxh9gGXT?= =?us-ascii?Q?2RCcg6+N0ipFKoQ5OtSKEp9S4nPcJGwJoKIvp5iUX6mH0Ha8/JP+Q6DvknSy?= =?us-ascii?Q?IM7LwaByrT8rIxENe9p8jm7gjMkHIiEtORhoeVr8ORaPRZUT4M3uqoPse3ug?= =?us-ascii?Q?4LetwHM5xpPgyLtCB3KMjBE1uUUan7UUZn6Adpa4J4YAvB43f8RZT3RWjxu9?= =?us-ascii?Q?FaFKoshmh3XMHKf6I1DnzM3Jm2SxjPIGjMfBOjmUnhSOGauoRn26eyVN+cma?= =?us-ascii?Q?pPaeJwt0yE1caDi3MfMkk+GyIo29aPr3xyBlgQUvbdc2ehsVK/LZUv+/QtNN?= =?us-ascii?Q?5/89cMQpvugM2Lo1MgW8aR7ktHOSFILt+rlmC0axt+0ApnV9tWuo5V7HDZ3x?= =?us-ascii?Q?z/Zlc7/e8LRV1GGqthwjTmbqZQ8N/CVnwwmqJyRp6uzba8VH52KgD2o/wv0l?= =?us-ascii?Q?voGAG0ajCpqrUCQHM2movR6jNJsqNQYCG9rjVLbimkvaxwSrFn9AnpSxoC7M?= =?us-ascii?Q?LL2S3mpKQwXryioE9MoZDY7ygX6IgYuooETCztIEcwJ2SAA0LQLI648Pmfxw?= =?us-ascii?Q?Gz1tZ/7MtelG1P3o+kwJWZnFRb0KWYim9A0uEuki+9/dPwr7tRCoLTJos3fk?= =?us-ascii?Q?IWJL/Z/MkIBE/3a/BZBq1Y3IOrm6DEL76J5hRQiaJCUn992f?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 51df8c1f-f4ac-4034-5131-08df244c807e X-MS-Exchange-CrossTenant-AuthSource: PH0PR12MB7957.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Oct 2026 08:25:10.4074 (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: popHk7ulvtg8jI0392LAYctqU4jfBVqUjG+fqd2ylkvzva8mOHW0rbWf6/Ad9TBcgBTl1WrGeePQaeEg4zzJAg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: LV5PR12MB9754 On Tue, Oct 06, 2026 at 03:41:18PM -0700, Kyle Zeng wrote: > RTM_GETNEIGHTBL exposes the live hash multiplier and bucket mask. For > ARP, that multiplier is applied to the IPv4 key XOR hash32_ptr(dev). > Since hash32_ptr() merely folds the address, timing chosen-key misses > through the unprivileged SIOCGARP ioctl can reveal the folded address > of the loopback net_device. NDISC uses the same address-dependent > first hash term. > > Give each net_device an independent random neighbour hash discriminator > at allocation time and use it in both protocol hashes. Keep it immutable > so that lookups, insertion and rehashing agree even if the device's > ifindex or network namespace changes. This retains the cross-namespace > hash distribution that motivated using the device pointer, without > putting a kernel address into the observable hash. A dedicated value > also avoids making a salt used by unrelated network hashes observable. > > The existing NDTA_CONFIG fields and neighbour key comparisons can stay > unchanged. Update the net_device cacheline documentation and assertions > for the new read-mostly field. > > Fixes: b14f243a42c7 ("net: Dont use ifindices in hash fns") > Assisted-by: Codex:gpt-6-astra > Signed-off-by: Kyle Zeng > --- > Documentation/networking/net_cachelines/net_device.rst | 1 + > include/linux/netdevice.h | 2 ++ > include/net/arp.h | 3 +-- > include/net/ndisc.h | 3 +-- > net/core/dev.c | 4 +++- > 5 files changed, 8 insertions(+), 5 deletions(-) Eric, Given [1], do you think this should be targeted at net-next? In net-next the neighbour tables are per-netns, so we can return to hashing based on the device index instead of its pointer. Something like [2]. [1] https://lore.kernel.org/netdev/CAL4WiiqWwV+8JaYjsHrWDvoSt8Ng01xs9Orv4xhRpFAvhMnD6w@mail.gmail.com/ [2] diff --git a/include/net/arp.h b/include/net/arp.h index e932def63d62..9e583624f5b2 100644 --- a/include/net/arp.h +++ b/include/net/arp.h @@ -4,7 +4,6 @@ #define _ARP_H #include -#include #include static inline struct neigh_table *arp_table(struct net *net) @@ -15,7 +14,7 @@ static inline struct neigh_table *arp_table(struct net *net) static inline u32 arp_hashfn(const void *pkey, const struct net_device *dev, u32 *hash_rnd) { u32 key = *(const u32 *)pkey; - u32 val = key ^ hash32_ptr(dev); + u32 val = key ^ dev->ifindex; return val * hash_rnd[0]; } diff --git a/include/net/ndisc.h b/include/net/ndisc.h index 96e3bb6e83af..a97be2e69409 100644 --- a/include/net/ndisc.h +++ b/include/net/ndisc.h @@ -54,7 +54,6 @@ enum { #include #include #include -#include #include @@ -355,7 +354,7 @@ static inline u32 ndisc_hashfn(const void *pkey, const struct net_device *dev, _ { const u32 *p32 = pkey; - return (((p32[0] ^ hash32_ptr(dev)) * hash_rnd[0]) + + return (((p32[0] ^ dev->ifindex) * hash_rnd[0]) + (p32[1] * hash_rnd[1]) + (p32[2] * hash_rnd[2]) + (p32[3] * hash_rnd[3]));