syzbot
KASAN: use-after-free Read in rcu_segcblist_accelerate
Status:
premoderation: reported on 2026/07/13 09:26
Reported-by: syzbot+b9b41cc8b02e6b34e97d@syzkaller.appspotmail.com
First crash: 86d, last: 14d
Sample crash report:
==================================================================
BUG: KASAN: use-after-free in rcu_segcblist_restempty kernel/rcu/rcu_segcblist.h:112 [inline]
BUG: KASAN: use-after-free in rcu_segcblist_accelerate+0x1e7/0x420 kernel/rcu/rcu_segcblist.c:579
Read of size 8 at addr ffff8881124dc590 by task udevd/327
CPU: 1 PID: 327 Comm: udevd 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:88
dump_stack_lvl+0x110/0x170 lib/dump_stack.c:106
print_address_description+0x71/0x200 mm/kasan/report.c:316
print_report+0x4a/0x60 mm/kasan/report.c:420
kasan_report+0x122/0x150 mm/kasan/report.c:524
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report_generic.c:351
rcu_segcblist_restempty kernel/rcu/rcu_segcblist.h:112 [inline]
rcu_segcblist_accelerate+0x1e7/0x420 kernel/rcu/rcu_segcblist.c:579
rcu_accelerate_cbs kernel/rcu/tree.c:1150 [inline]
rcu_report_qs_rdp kernel/rcu/tree.c:2088 [inline]
rcu_check_quiescent_state kernel/rcu/tree.c:2141 [inline]
rcu_core+0x7b5/0xf00 kernel/rcu/tree.c:2541
rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2574
handle_softirqs+0x1d7/0x600 kernel/softirq.c:642
__do_softirq kernel/softirq.c:680 [inline]
invoke_softirq kernel/softirq.c:497 [inline]
__irq_exit_rcu+0x52/0xf0 kernel/softirq.c:729
irq_exit_rcu+0x9/0x10 kernel/softirq.c:741
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
sysvec_apic_timer_interrupt+0xa9/0xc0 arch/x86/kernel/apic/apic.c:1118
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1b/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:node_maxindex lib/radix-tree.c:216 [inline]
RIP: 0010:radix_tree_load_root lib/radix-tree.c:395 [inline]
RIP: 0010:__radix_tree_lookup lib/radix-tree.c:756 [inline]
RIP: 0010:radix_tree_lookup+0x7c/0x290 lib/radix-tree.c:817
Code: bf 02 00 00 00 4c 89 e6 e8 b1 b5 7f fc 49 83 fc 02 0f 85 fb 01 00 00 4d 89 fc 49 83 e4 fc 4c 89 f8 48 c1 e8 03 42 0f b6 04 30 <84> c0 0f 85 86 01 00 00 45 0f b6 24 24 bf 40 00 00 00 44 89 e6 e8
RSP: 0018:ffffc9000dc4fe40 EFLAGS: 00000a02
RAX: 0000000000000000 RBX: 000000000000003b RCX: ffff88810f329440
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000002
RBP: ffffc9000dc4fe78 R08: ffff88810fe498b3 R09: 1ffff11021fc9316
R10: dffffc0000000000 R11: ffffed1021fc9317 R12: ffff88810c0a8840
R13: 000000000000003b R14: dffffc0000000000 R15: ffff88810c0a8842
idr_find+0x41/0x60 lib/idr.c:176
inotify_idr_find_locked fs/notify/inotify/inotify_user.c:424 [inline]
inotify_idr_find fs/notify/inotify/inotify_user.c:443 [inline]
__do_sys_inotify_rm_watch fs/notify/inotify/inotify_user.c:830 [inline]
__se_sys_inotify_rm_watch+0xf0/0x230 fs/notify/inotify/inotify_user.c:813
__x64_sys_inotify_rm_watch+0x5b/0x70 fs/notify/inotify/inotify_user.c:813
x64_sys_call+0x6d4/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:256
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fd795921a07
Code: 73 01 c3 48 8b 0d f1 f3 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 ff 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d c1 f3 0c 00 f7 d8 64 89 01 48
RSP: 002b:00007fffae9bf778 EFLAGS: 00000246 ORIG_RAX: 00000000000000ff
RAX: ffffffffffffffda RBX: 000055c09d306180 RCX: 00007fd795921a07
RDX: 0000000000000007 RSI: 000000000000003b RDI: 0000000000000007
RBP: 000000000000003b R08: 00000000000001e0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fffae9bf780
R13: 0000000003938700 R14: 000055c095347100 R15: 000055c095347140
</TASK>
Allocated by task 347:
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
kasan_save_alloc_info+0x1f/0x30 mm/kasan/generic.c:505
____kasan_kmalloc mm/kasan/common.c:380 [inline]
__kasan_kmalloc+0x95/0xb0 mm/kasan/common.c:389
kasan_kmalloc include/linux/kasan.h:212 [inline]
__do_kmalloc_node mm/slab_common.c:938 [inline]
__kmalloc+0xb4/0x1e0 mm/slab_common.c:951
kmalloc include/linux/slab.h:568 [inline]
kzalloc include/linux/slab.h:699 [inline]
l2tp_session_create+0x38/0xbd0 net/l2tp/l2tp_core.c:1614
pppol2tp_connect+0xbf5/0x1640 net/l2tp/l2tp_ppp.c:771
__sys_connect_file net/socket.c:2001 [inline]
__sys_connect+0x3da/0x460 net/socket.c:2018
__do_sys_connect net/socket.c:2028 [inline]
__se_sys_connect net/socket.c:2025 [inline]
__x64_sys_connect+0x7a/0x90 net/socket.c:2025
x64_sys_call+0x88d/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:43
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
Freed by task 43:
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:516
____kasan_slab_free+0x132/0x180 mm/kasan/common.c:242
__kasan_slab_free+0x11/0x20 mm/kasan/common.c:250
kasan_slab_free include/linux/kasan.h:178 [inline]
slab_free_hook mm/slub.c:1750 [inline]
slab_free_freelist_hook+0xc2/0x190 mm/slub.c:1776
slab_free mm/slub.c:3712 [inline]
__kmem_cache_free+0xb7/0x1b0 mm/slub.c:3728
kfree+0x6f/0xf0 mm/slab_common.c:990
l2tp_session_free net/l2tp/l2tp_core.c:168 [inline]
l2tp_session_put+0xaf/0x1a0 net/l2tp/l2tp_core.c:193
l2tp_session_delete+0x3df/0x4d0 net/l2tp/l2tp_core.c:1587
l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1233 [inline]
l2tp_tunnel_del_work+0x199/0x410 net/l2tp/l2tp_core.c:1271
process_one_work+0x717/0xc30 kernel/workqueue.c:2302
worker_thread+0xa4d/0x11d0 kernel/workqueue.c:2449
kthread+0x281/0x320 kernel/kthread.c:386
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
Last potentially related work creation:
kasan_save_stack+0x3a/0x60 mm/kasan/common.c:46
__kasan_record_aux_stack+0xb6/0xc0 mm/kasan/generic.c:486
kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:496
__call_rcu_common kernel/rcu/tree.c:2807 [inline]
call_rcu+0xcf/0xf50 kernel/rcu/tree.c:2926
pppol2tp_release+0x1e3/0x2b0 net/l2tp/l2tp_ppp.c:446
__sock_release net/socket.c:652 [inline]
sock_close+0xc9/0x220 net/socket.c:1390
__fput+0x1fd/0x8f0 fs/file_table.c:320
____fput+0x15/0x20 fs/file_table.c:348
task_work_run+0x1e1/0x250 kernel/task_work.c:203
exit_task_work include/linux/task_work.h:39 [inline]
do_exit+0xb0d/0x29f0 kernel/exit.c:896
__do_sys_exit kernel/exit.c:1006 [inline]
__se_sys_exit kernel/exit.c:1004 [inline]
__cfi___ia32_sys_exit+0x0/0x10 kernel/exit.c:1004
x64_sys_call+0x67/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:61
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
The buggy address belongs to the object at ffff8881124dc400
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 400 bytes inside of
512-byte region [ffff8881124dc400, ffff8881124dc600)
The buggy address belongs to the physical page:
page:ffffea0004493700 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1124dc
head:ffffea0004493700 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 0000000000000000 dead000000000122 ffff888100042f00
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 0x1d2a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 24, tgid 24 (kworker/1:0), ts 26612751527, free_ts 26601868160
set_page_owner include/linux/page_owner.h:33 [inline]
post_alloc_hook+0x1f5/0x210 mm/page_alloc.c:2673
prep_new_page+0x1c/0x110 mm/page_alloc.c:2680
get_page_from_freelist+0x2ca9/0x2d20 mm/page_alloc.c:4587
__alloc_pages+0x1fa/0x610 mm/page_alloc.c:5931
alloc_slab_page+0x6e/0xf0 include/linux/gfp.h:-1
allocate_slab mm/slub.c:1967 [inline]
new_slab+0x98/0x3e0 mm/slub.c:2020
___slab_alloc+0x70f/0xb70 mm/slub.c:3177
__slab_alloc+0x5e/0xa0 mm/slub.c:3263
slab_alloc_node mm/slub.c:3348 [inline]
__kmem_cache_alloc_node+0x204/0x2d0 mm/slub.c:3423
__do_kmalloc_node mm/slab_common.c:937 [inline]
__kmalloc_node_track_caller+0xa1/0x1e0 mm/slab_common.c:958
kmalloc_reserve net/core/skbuff.c:449 [inline]
__alloc_skb+0x226/0x4a0 net/core/skbuff.c:518
alloc_skb include/linux/skbuff.h:1322 [inline]
ndisc_alloc_skb net/ipv6/ndisc.c:423 [inline]
ndisc_send_rs+0x31d/0x870 net/ipv6/ndisc.c:707
addrconf_dad_completed+0x958/0xe80 net/ipv6/addrconf.c:4322
addrconf_dad_work+0xc1b/0x14a0 net/ipv6/addrconf.c:-1
process_one_work+0x717/0xc30 kernel/workqueue.c:2302
worker_thread+0xa4d/0x11d0 kernel/workqueue.c:2449
page last free stack trace:
reset_page_owner include/linux/page_owner.h:26 [inline]
free_pages_prepare mm/page_alloc.c:1581 [inline]
free_pcp_prepare mm/page_alloc.c:1655 [inline]
free_unref_page_prepare+0x81b/0x820 mm/page_alloc.c:3622
free_unref_page+0x93/0x530 mm/page_alloc.c:3720
free_the_page mm/page_alloc.c:863 [inline]
__free_pages+0x67/0x100 mm/page_alloc.c:6021
free_pages+0x82/0x90 mm/page_alloc.c:6032
__stack_depot_save+0x45f/0x490 lib/stackdepot.c:506
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_set_track+0x60/0x70 mm/kasan/common.c:53
kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:516
____kasan_slab_free+0x132/0x180 mm/kasan/common.c:242
__kasan_slab_free+0x11/0x20 mm/kasan/common.c:250
kasan_slab_free include/linux/kasan.h:178 [inline]
slab_free_hook mm/slub.c:1750 [inline]
slab_free_freelist_hook+0xc2/0x190 mm/slub.c:1776
slab_free mm/slub.c:3712 [inline]
__kmem_cache_free+0xb7/0x1b0 mm/slub.c:3728
kfree+0x6f/0xf0 mm/slab_common.c:990
kfree_const+0x39/0x40 mm/util.c:46
kernfs_put+0x1be/0x480 fs/kernfs/dir.c:559
kernfs_remove_by_name_ns+0xea/0x160 fs/kernfs/dir.c:1701
kernfs_remove_by_name include/linux/kernfs.h:635 [inline]
sysfs_remove_link+0x50/0x60 fs/sysfs/symlink.c:152
Memory state around the buggy address:
ffff8881124dc480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8881124dc500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8881124dc580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8881124dc600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8881124dc680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================
----------------
Code disassembly (best guess):
0: bf 02 00 00 00 mov $0x2,%edi
5: 4c 89 e6 mov %r12,%rsi
8: e8 b1 b5 7f fc call 0xfc7fb5be
d: 49 83 fc 02 cmp $0x2,%r12
11: 0f 85 fb 01 00 00 jne 0x212
17: 4d 89 fc mov %r15,%r12
1a: 49 83 e4 fc and $0xfffffffffffffffc,%r12
1e: 4c 89 f8 mov %r15,%rax
21: 48 c1 e8 03 shr $0x3,%rax
25: 42 0f b6 04 30 movzbl (%rax,%r14,1),%eax
* 2a: 84 c0 test %al,%al <-- trapping instruction
2c: 0f 85 86 01 00 00 jne 0x1b8
32: 45 0f b6 24 24 movzbl (%r12),%r12d
37: bf 40 00 00 00 mov $0x40,%edi
3c: 44 89 e6 mov %r12d,%esi
3f: e8 .byte 0xe8
Struck through repros no longer work on HEAD.