CVE-2025-68801: In the Linux kernel, the following vulnerability has been resolved:  mlxsw: spectrum_router: Fix neighbour use-after-free  We sometimes observe use-after-free when dereferencing a neighbour [1]. The problem seems to be that the driver stores a pointer to the neighbour, but without holding a reference on it. A reference is only taken when the neighbour is used by a nexthop.  Fix by simplifying the reference counting scheme. Always take a reference when storing a neighbour pointer in a neighbour entry. Avoid taking a referencing when the neighbour is used by a nexthop as the neighbour entry associated with the nexthop already holds a reference.  Tested by running the test that uncovered the problem over 300 times. Without this patch the problem was reproduced after a handful of iterations.  [1] BUG: KASAN: slab-use-after-free in mlxsw_sp_neigh_entry_update+0x2d4/0x310 Read of size 8 at addr ffff88817f8e3420 by task ip/3929  CPU: 3 UID: 0 PID: 3929 Comm: ip Not tainted 6.18.0-rc4-virtme-g36b21a067510 #3 PREEMPT(full) Hardware name: Nvidia SN5600/VMOD0013, BIOS 5.13 05/31/2023 Call Trace:  <TASK>  dump_stack_lvl+0x6f/0xa0  print_address_description.constprop.0+0x6e/0x300  print_report+0xfc/0x1fb  kasan_report+0xe4/0x110  mlxsw_sp_neigh_entry_update+0x2d4/0x310  mlxsw_sp_router_rif_gone_sync+0x35f/0x510  mlxsw_sp_rif_destroy+0x1ea/0x730  mlxsw_sp_inetaddr_port_vlan_event+0xa1/0x1b0  __mlxsw_sp_inetaddr_lag_event+0xcc/0x130  __mlxsw_sp_inetaddr_event+0xf5/0x3c0  mlxsw_sp_router_netdevice_event+0x1015/0x1580  notifier_call_chain+0xcc/0x150  call_netdevice_notifiers_info+0x7e/0x100  __netdev_upper_dev_unlink+0x10b/0x210  netdev_upper_dev_unlink+0x79/0xa0  vrf_del_slave+0x18/0x50  do_set_master+0x146/0x7d0  do_setlink.isra.0+0x9a0/0x2880  rtnl_newlink+0x637/0xb20  rtnetlink_rcv_msg+0x6fe/0xb90  netlink_rcv_skb+0x123/0x380  netlink_unicast+0x4a3/0x770  netlink_sendmsg+0x75b/0xc90  __sock_sendmsg+0xbe/0x160  ____sys_sendmsg+0x5b2/0x7d0  ___sys_sendmsg+0xfd/0x180  __sys_sendmsg+0x124/0x1c0  do_syscall_64+0xbb/0xfd0  entry_SYSCALL_64_after_hwframe+0x4b/0x53 [...]  Allocated by task 109:  kasan_save_stack+0x30/0x50  kasan_save_track+0x14/0x30  __kasan_kmalloc+0x7b/0x90  __kmalloc_noprof+0x2c1/0x790  neigh_alloc+0x6af/0x8f0  ___neigh_create+0x63/0xe90  mlxsw_sp_nexthop_neigh_init+0x430/0x7e0  mlxsw_sp_nexthop_type_init+0x212/0x960  mlxsw_sp_nexthop6_group_info_init.constprop.0+0x81f/0x1280  mlxsw_sp_nexthop6_group_get+0x392/0x6a0  mlxsw_sp_fib6_entry_create+0x46a/0xfd0  mlxsw_sp_router_fib6_replace+0x1ed/0x5f0  mlxsw_sp_router_fib6_event_work+0x10a/0x2a0  process_one_work+0xd57/0x1390  worker_thread+0x4d6/0xd40  kthread+0x355/0x5b0  ret_from_fork+0x1d4/0x270  ret_from_fork_asm+0x11/0x20  Freed by task 154:  kasan_save_stack+0x30/0x50  kasan_save_track+0x14/0x30  __kasan_save_free_info+0x3b/0x60  __kasan_slab_free+0x43/0x70  kmem_cache_free_bulk.part.0+0x1eb/0x5e0  kvfree_rcu_bulk+0x1f2/0x260  kfree_rcu_work+0x130/0x1b0  process_one_work+0xd57/0x1390  worker_thread+0x4d6/0xd40  kthread+0x355/0x5b0  ret_from_fork+0x1d4/0x270  ret_from_fork_asm+0x11/0x20  Last potentially related work creation:  kasan_save_stack+0x30/0x50  kasan_record_aux_stack+0x8c/0xa0  kvfree_call_rcu+0x93/0x5b0  mlxsw_sp_router_neigh_event_work+0x67d/0x860  process_one_work+0xd57/0x1390  worker_thread+0x4d6/0xd40  kthread+0x355/0x5b0  ret_from_fork+0x1d4/0x270  ret_from_fork_asm+0x11/0x20