CVE-2026-23004

In the Linux kernel, the following vulnerability has been resolved:

dst: fix races in rt6_uncached_list_del() and rt_del_uncached_list()

syzbot was able to crash the kernel in rt6_uncached_list_flush_dev()

in an interesting way [1]

Crash happens in list_del_init()/INIT_LIST_HEAD() while writing

list->prev, while the prior write on list->next went well.

static inline void INIT_LIST_HEAD(struct list_head *list)

{

WRITE_ONCE(list->next, list); // This went well

WRITE_ONCE(list->prev, list); // Crash, @list has been freed.

}

Issue here is that rt6_uncached_list_del() did not attempt to lock

ul->lock, as list_empty(&rt->dst.rt_uncached) returned

true because the WRITE_ONCE(list->next, list) happened on the other CPU.

We might use list_del_init_careful() and list_empty_careful(),

or make sure rt6_uncached_list_del() always grabs the spinlock

whenever rt->dst.rt_uncached_list has been set.

A similar fix is neeed for IPv4.

[1]

BUG: KASAN: slab-use-after-free in INIT_LIST_HEAD include/linux/list.h:46 [inline]

BUG: KASAN: slab-use-after-free in list_del_init include/linux/list.h:296 [inline]

BUG: KASAN: slab-use-after-free in rt6_uncached_list_flush_dev net/ipv6/route.c:191 [inline]

BUG: KASAN: slab-use-after-free in rt6_disable_ip+0x633/0x730 net/ipv6/route.c:5020

Write of size 8 at addr ffff8880294cfa78 by task kworker/u8:14/3450

CPU: 0 UID: 0 PID: 3450 Comm: kworker/u8:14 Tainted: G L syzkaller #0 PREEMPT_{RT,(full)}

Tainted: [L]=SOFTLOCKUP

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025

Workqueue: netns cleanup_net

Call Trace:

<TASK>

dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120

print_address_description mm/kasan/report.c:378 [inline]

print_report+0xca/0x240 mm/kasan/report.c:482

kasan_report+0x118/0x150 mm/kasan/report.c:595

INIT_LIST_HEAD include/linux/list.h:46 [inline]

list_del_init include/linux/list.h:296 [inline]

rt6_uncached_list_flush_dev net/ipv6/route.c:191 [inline]

rt6_disable_ip+0x633/0x730 net/ipv6/route.c:5020

addrconf_ifdown+0x143/0x18a0 net/ipv6/addrconf.c:3853

addrconf_notify+0x1bc/0x1050 net/ipv6/addrconf.c:-1

notifier_call_chain+0x19d/0x3a0 kernel/notifier.c:85

call_netdevice_notifiers_extack net/core/dev.c:2268 [inline]

call_netdevice_notifiers net/core/dev.c:2282 [inline]

netif_close_many+0x29c/0x410 net/core/dev.c:1785

unregister_netdevice_many_notify+0xb50/0x2330 net/core/dev.c:12353

ops_exit_rtnl_list net/core/net_namespace.c:187 [inline]

ops_undo_list+0x3dc/0x990 net/core/net_namespace.c:248

cleanup_net+0x4de/0x7b0 net/core/net_namespace.c:696

process_one_work kernel/workqueue.c:3257 [inline]

process_scheduled_works+0xad1/0x1770 kernel/workqueue.c:3340

worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421

kthread+0x711/0x8a0 kernel/kthread.c:463

ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158

ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

</TASK>

Allocated by task 803:

kasan_save_stack mm/kasan/common.c:57 [inline]

kasan_save_track+0x3e/0x80 mm/kasan/common.c:78

unpoison_slab_object mm/kasan/common.c:340 [inline]

__kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:366

kasan_slab_alloc include/linux/kasan.h:253 [inline]

slab_post_alloc_hook mm/slub.c:4953 [inline]

slab_alloc_node mm/slub.c:5263 [inline]

kmem_cache_alloc_noprof+0x18d/0x6c0 mm/slub.c:5270

dst_alloc+0x105/0x170 net/core/dst.c:89

ip6_dst_alloc net/ipv6/route.c:342 [inline]

icmp6_dst_alloc+0x75/0x460 net/ipv6/route.c:3333

mld_sendpack+0x683/0xe60 net/ipv6/mcast.c:1844

mld_send_cr net/ipv6/mcast.c:2154 [inline]

mld_ifc_work+0x83e/0xd60 net/ipv6/mcast.c:2693

process_one_work kernel/workqueue.c:3257 [inline]

process_scheduled_works+0xad1/0x1770 kernel/workqueue.c:3340

worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421

kthread+0x711/0x8a0 kernel/kthread.c:463

ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158

ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entr

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