syzbot
KASAN: use-after-free Read in rcu_segcblist_accelerate
Status:
premoderation: reported on 2026/09/02 16:43
Reported-by: syzbot+74a7eb681ba4ab622031@syzkaller.appspotmail.com
First crash: 43d, last: 26d
Sample crash report:
==================================================================
BUG: KASAN: use-after-free in rcu_segcblist_restempty kernel/rcu/rcu_segcblist.h:75 [inline]
BUG: KASAN: use-after-free in rcu_segcblist_accelerate+0x1e1/0x320 kernel/rcu/rcu_segcblist.c:487
Read of size 8 at addr ffff88810de2f590 by task swapper/1/0
CPU: 1 PID: 0 Comm: swapper/1 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
<IRQ>
__dump_stack+0x21/0x24 lib/dump_stack.c:77
dump_stack_lvl+0x1a7/0x208 lib/dump_stack.c:118
print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
__kasan_report mm/kasan/report.c:435 [inline]
kasan_report+0x100/0x140 mm/kasan/report.c:452
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report_generic.c:309
rcu_segcblist_restempty kernel/rcu/rcu_segcblist.h:75 [inline]
rcu_segcblist_accelerate+0x1e1/0x320 kernel/rcu/rcu_segcblist.c:487
rcu_accelerate_cbs+0x59/0x430 kernel/rcu/tree.c:1510
rcu_advance_cbs kernel/rcu/tree.c:1575 [inline]
__note_gp_changes+0x1c5/0x760 kernel/rcu/tree.c:1629
note_gp_changes+0x131/0x230 kernel/rcu/tree.c:1675
rcu_check_quiescent_state kernel/rcu/tree.c:2319 [inline]
rcu_core+0x249/0xca0 kernel/rcu/tree.c:2719
rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2748
__do_softirq+0x255/0x563 kernel/softirq.c:309
asm_call_irq_on_stack+0xf/0x20
</IRQ>
__run_on_irqstack arch/x86/include/asm/irq_stack.h:26 [inline]
run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:77 [inline]
do_softirq_own_stack+0x60/0x80 arch/x86/kernel/irq_64.c:77
invoke_softirq kernel/softirq.c:405 [inline]
__irq_exit_rcu+0x128/0x150 kernel/softirq.c:435
irq_exit_rcu+0x9/0x10 kernel/softirq.c:447
sysvec_apic_timer_interrupt+0xbf/0xe0 arch/x86/kernel/apic/apic.c:1106
asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:635
RIP: 0010:default_idle+0x12/0x20 arch/x86/kernel/process.c:718
Code: 49 bd 00 00 00 00 00 fc ff df e9 68 ff ff ff e8 b4 f7 fa ff 00 00 cc cc 55 48 89 e5 0f 1f 44 00 00 0f 00 2d 40 ad 62 00 fb f4 <5d> c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 55 48 89 e5 41 57 41 56
RSP: 0018:ffffc90000107db8 EFLAGS: 00000246
RAX: ffff8881f7100000 RBX: ffff888100296400 RCX: 0000000000034b46
RDX: 0000000000000001 RSI: ffffffff85406c40 RDI: ffffffff85406c00
RBP: ffffc90000107db8 R08: ffff8881f71573d3 R09: 1ffff1103ee2ae7a
R10: dffffc0000000000 R11: ffffed103ee2ae7b R12: 0000000000000000
R13: 1ffff11020052c80 R14: dffffc0000000000 R15: dffffc0000000000
arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:709
default_idle_call+0x71/0x1d0 kernel/sched/idle.c:114
cpuidle_idle_call kernel/sched/idle.c:204 [inline]
do_idle+0x368/0x620 kernel/sched/idle.c:328
cpu_startup_entry+0x18/0x20 kernel/sched/idle.c:425
start_secondary+0x2cb/0x380 arch/x86/kernel/smpboot.c:276
secondary_startup_64_no_verify+0xad/0xbb
Allocated by task 2436:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track mm/kasan/common.c:45 [inline]
set_alloc_info mm/kasan/common.c:430 [inline]
____kasan_kmalloc mm/kasan/common.c:509 [inline]
__kasan_kmalloc+0xd4/0x100 mm/kasan/common.c:518
kasan_kmalloc include/linux/kasan.h:254 [inline]
__kmalloc+0x19f/0x330 mm/slub.c:4038
kmalloc include/linux/slab.h:560 [inline]
kzalloc include/linux/slab.h:667 [inline]
l2tp_session_create+0x39/0xb60 net/l2tp/l2tp_core.c:1616
pppol2tp_connect+0xbf5/0x1640 net/l2tp/l2tp_ppp.c:772
__sys_connect_file net/socket.c:1867 [inline]
__sys_connect+0x3ce/0x450 net/socket.c:1884
__do_sys_connect net/socket.c:1894 [inline]
__se_sys_connect net/socket.c:1891 [inline]
__x64_sys_connect+0x7a/0x90 net/socket.c:1891
do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x61/0xcb
Freed by task 304:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track+0x4a/0x70 mm/kasan/common.c:45
kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:370
____kasan_slab_free+0x125/0x160 mm/kasan/common.c:362
__kasan_slab_free+0x11/0x20 mm/kasan/common.c:370
kasan_slab_free include/linux/kasan.h:220 [inline]
slab_free_hook mm/slub.c:1600 [inline]
slab_free_freelist_hook+0xc5/0x190 mm/slub.c:1626
slab_free mm/slub.c:3208 [inline]
kfree+0xc0/0x270 mm/slub.c:4196
l2tp_session_free net/l2tp/l2tp_core.c:168 [inline]
l2tp_session_put+0xb2/0x1a0 net/l2tp/l2tp_core.c:193
l2tp_session_delete+0x3a9/0x4a0 net/l2tp/l2tp_core.c:1589
l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1235 [inline]
l2tp_tunnel_del_work+0x180/0x3d0 net/l2tp/l2tp_core.c:1273
process_one_work+0x6fd/0xbc0 kernel/workqueue.c:2301
worker_thread+0xa8e/0x13c0 kernel/workqueue.c:2447
kthread+0x324/0x3b0 kernel/kthread.c:313
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298
Last potentially related work creation:
kasan_save_stack+0x3a/0x60 mm/kasan/common.c:38
__kasan_record_aux_stack+0xd2/0x100 mm/kasan/generic.c:348
kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:358
__call_rcu kernel/rcu/tree.c:2980 [inline]
call_rcu+0x11a/0x1090 kernel/rcu/tree.c:3054
pppol2tp_release+0x1e3/0x2b0 net/l2tp/l2tp_ppp.c:447
__sock_release net/socket.c:597 [inline]
sock_close+0xb8/0x200 net/socket.c:1287
__fput+0x2dc/0x730 fs/file_table.c:281
____fput+0x15/0x20 fs/file_table.c:314
task_work_run+0x127/0x190 kernel/task_work.c:189
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_user_mode_loop+0xcb/0xe0 kernel/entry/common.c:172
exit_to_user_mode_prepare+0x76/0xa0 kernel/entry/common.c:199
syscall_exit_to_user_mode+0x1d/0x40 kernel/entry/common.c:274
do_syscall_64+0x3d/0x40 arch/x86/entry/common.c:56
entry_SYSCALL_64_after_hwframe+0x61/0xcb
The buggy address belongs to the object at ffff88810de2f400
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 400 bytes inside of
512-byte region [ffff88810de2f400, ffff88810de2f600)
The buggy address belongs to the page:
page:ffffea0004378b00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10de2c
head:ffffea0004378b00 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head)
raw: 4000000000010200 dead000000000100 dead000000000122 ffff888100043080
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0x152a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_HARDWALL), pid 20, ts 35363110954, free_ts 35340840758
set_page_owner include/linux/page_owner.h:35 [inline]
post_alloc_hook mm/page_alloc.c:2456 [inline]
prep_new_page+0x176/0x190 mm/page_alloc.c:2462
get_page_from_freelist+0x225f/0x23f0 mm/page_alloc.c:4254
__alloc_pages_nodemask+0x29a/0x640 mm/page_alloc.c:5384
alloc_slab_page mm/slub.c:-1 [inline]
allocate_slab mm/slub.c:1813 [inline]
new_slab+0x84/0x3f0 mm/slub.c:1874
new_slab_objects mm/slub.c:2632 [inline]
___slab_alloc+0x2f8/0x4c0 mm/slub.c:2796
__slab_alloc+0x63/0xa0 mm/slub.c:2836
slab_alloc_node mm/slub.c:2918 [inline]
slab_alloc mm/slub.c:2960 [inline]
__kmalloc+0x1f9/0x330 mm/slub.c:4034
kmalloc include/linux/slab.h:560 [inline]
kzalloc include/linux/slab.h:667 [inline]
neigh_alloc net/core/neighbour.c:439 [inline]
___neigh_create+0x6ec/0x1a70 net/core/neighbour.c:592
__neigh_create+0x31/0x40 net/core/neighbour.c:680
ip6_finish_output2+0x8fe/0x1540 net/ipv6/ip6_output.c:129
__ip6_finish_output+0x5fd/0x790 net/ipv6/ip6_output.c:203
ip6_finish_output+0x33/0x1e0 net/ipv6/ip6_output.c:213
NF_HOOK_COND include/linux/netfilter.h:288 [inline]
ip6_output+0x1fa/0x420 net/ipv6/ip6_output.c:236
dst_output include/net/dst.h:451 [inline]
NF_HOOK include/linux/netfilter.h:299 [inline]
ndisc_send_skb+0x721/0xbc0 net/ipv6/ndisc.c:513
ndisc_send_rs+0x711/0x960 net/ipv6/ndisc.c:707
addrconf_dad_completed+0x945/0xe30 net/ipv6/addrconf.c:4293
page last free stack trace:
reset_page_owner include/linux/page_owner.h:28 [inline]
free_pages_prepare mm/page_alloc.c:1349 [inline]
free_pcp_prepare mm/page_alloc.c:1421 [inline]
free_unref_page_prepare+0x2b7/0x2d0 mm/page_alloc.c:3336
free_unref_page mm/page_alloc.c:3391 [inline]
free_the_page mm/page_alloc.c:5443 [inline]
__free_pages+0x146/0x390 mm/page_alloc.c:5454
__vunmap+0x801/0x980 mm/vmalloc.c:2307
__vfree mm/vmalloc.c:2356 [inline]
vfree+0x61/0x90 mm/vmalloc.c:2387
kvm_arch_free_vm+0x44/0x50 arch/x86/kvm/x86.c:10658
kvm_destroy_vm virt/kvm/kvm_main.c:952 [inline]
kvm_put_kvm+0xf04/0x10a0 virt/kvm/kvm_main.c:968
kvm_vm_release+0x46/0x50 virt/kvm/kvm_main.c:991
__fput+0x2dc/0x730 fs/file_table.c:281
____fput+0x15/0x20 fs/file_table.c:314
task_work_run+0x127/0x190 kernel/task_work.c:189
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_user_mode_loop+0xcb/0xe0 kernel/entry/common.c:172
exit_to_user_mode_prepare+0x76/0xa0 kernel/entry/common.c:199
syscall_exit_to_user_mode+0x1d/0x40 kernel/entry/common.c:274
do_syscall_64+0x3d/0x40 arch/x86/entry/common.c:56
entry_SYSCALL_64_after_hwframe+0x61/0xcb
Memory state around the buggy address:
ffff88810de2f480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88810de2f500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88810de2f580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88810de2f600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88810de2f680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================
----------------
Code disassembly (best guess):
0: 49 bd 00 00 00 00 00 movabs $0xdffffc0000000000,%r13
7: fc ff df
a: e9 68 ff ff ff jmp 0xffffff77
f: e8 b4 f7 fa ff call 0xfffaf7c8
14: 00 00 add %al,(%rax)
16: cc int3
17: cc int3
18: 55 push %rbp
19: 48 89 e5 mov %rsp,%rbp
1c: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
21: 0f 00 2d 40 ad 62 00 verw 0x62ad40(%rip) # 0x62ad68
28: fb sti
29: f4 hlt
* 2a: 5d pop %rbp <-- trapping instruction
2b: c3 ret
2c: 66 2e 0f 1f 84 00 00 cs nopw 0x0(%rax,%rax,1)
33: 00 00 00
36: 66 90 xchg %ax,%ax
38: 55 push %rbp
39: 48 89 e5 mov %rsp,%rbp
3c: 41 57 push %r15
3e: 41 56 push %r14
Struck through repros no longer work on HEAD.