KASAN: slab-use-after-free Read in pool_ctr

Status: upstream: reported C repro on 2026/10/26 02:06
Subsystems: dm
[Documentation on labels]
Reported-by: syzbot+83827f9a59abe148bff4@syzkaller.appspotmail.com
First crash: 4d06h, last: 4d03h
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ID Workflow Result Correct Bug Created Started Finished Revision
552f8171 assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ❌ FuzzingArtifact: ❌ MemoryCorruption: ✅ NetworkNeedsSetup: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KASAN: slab-use-after-free Read in pool_ctr 2026/10/23 00:49 2026/10/23 00:49 2026/10/23 01:36 33f73a1b
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[syzbot] [dm?] KASAN: slab-use-after-free Read in pool_ctr 0 (1) 2026/10/26 02:06

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in pool_ctr+0x874/0xd60 drivers/md/dm-thin.c:3363
Read of size 8 at addr ffff8880340cc698 by task syz.0.17/5507

CPU: 0 UID: 0 PID: 5507 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description+0x55/0x1e0 mm/kasan/report.c:378
 print_report+0x58/0x70 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 pool_ctr+0x874/0xd60 drivers/md/dm-thin.c:3363
 dm_table_add_target+0x58d/0xc70 drivers/md/dm-table.c:749
 populate_table drivers/md/dm-ioctl.c:1602 [inline]
 table_load+0x325/0x8a0 drivers/md/dm-ioctl.c:1645
 ctl_ioctl drivers/md/dm-ioctl.c:2221 [inline]
 dm_ctl_ioctl+0x9ec/0xe10 drivers/md/dm-ioctl.c:2243
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fad75f9f559
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe43dedf68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fad76225fa0 RCX: 00007fad75f9f559
RDX: 00002000000003c0 RSI: 00000000c138fd09 RDI: 0000000000000003
RBP: 00007fad76036b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fad76225fac R14: 00007fad76225fa0 R15: 00007fad76225fa0
 </TASK>

Allocated by task 5507:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:409 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:426
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_node_noprof+0x3cc/0x620 mm/slub.c:5582
 _kmalloc_node_noprof include/linux/slab.h:1196 [inline]
 open_table_device drivers/md/dm.c:733 [inline]
 dm_get_table_device+0x23e/0x730 drivers/md/dm.c:821
 dm_get_device+0x327/0x760 drivers/md/dm-table.c:388
 pool_ctr+0x4ae/0xd60 drivers/md/dm-thin.c:3329
 dm_table_add_target+0x58d/0xc70 drivers/md/dm-table.c:749
 populate_table drivers/md/dm-ioctl.c:1602 [inline]
 table_load+0x325/0x8a0 drivers/md/dm-ioctl.c:1645
 ctl_ioctl drivers/md/dm-ioctl.c:2221 [inline]
 dm_ctl_ioctl+0x9ec/0xe10 drivers/md/dm-ioctl.c:2243
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 5507:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:264 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:296
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2748 [inline]
 slab_free mm/slub.c:6509 [inline]
 kfree+0x1c5/0x650 mm/slub.c:6802
 close_table_device drivers/md/dm.c:798 [inline]
 dm_put_table_device+0x255/0x2a0 drivers/md/dm.c:841
 upgrade_mode drivers/md/dm-table.c:326 [inline]
 dm_get_device+0x56f/0x760 drivers/md/dm-table.c:399
 pool_ctr+0x585/0xd60 drivers/md/dm-thin.c:3336
 dm_table_add_target+0x58d/0xc70 drivers/md/dm-table.c:749
 populate_table drivers/md/dm-ioctl.c:1602 [inline]
 table_load+0x325/0x8a0 drivers/md/dm-ioctl.c:1645
 ctl_ioctl drivers/md/dm-ioctl.c:2221 [inline]
 dm_ctl_ioctl+0x9ec/0xe10 drivers/md/dm-ioctl.c:2243
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff8880340cc680
 which belongs to the cache kmalloc-96 of size 96
The buggy address is located 24 bytes inside of
 freed 96-byte region [ffff8880340cc680, ffff8880340cc6e0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x340cc
flags: 0x4fff00000000000(node=1|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 04fff00000000000 ffff88801c041280 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 2, tgid 2 (kthreadd), ts 9397553089
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f9/0x250 mm/page_alloc.c:1871
 prep_new_page mm/page_alloc.c:1879 [inline]
 get_page_from_freelist+0x2209/0x2280 mm/page_alloc.c:3943
 __alloc_frozen_pages_noprof+0x217/0x5a0 mm/page_alloc.c:5436
 alloc_slab_page mm/slub.c:3347 [inline]
 allocate_slab+0x7d/0x620 mm/slub.c:3462
 new_slab mm/slub.c:3513 [inline]
 refill_objects+0x2d5/0x350 mm/slub.c:7418
 refill_sheaf mm/slub.c:2885 [inline]
 __pcs_replace_empty_main+0x2c8/0x6c0 mm/slub.c:4774
 alloc_from_pcs mm/slub.c:4850 [inline]
 slab_alloc_node mm/slub.c:4984 [inline]
 __kmalloc_cache_node_noprof+0x446/0x620 mm/slub.c:5578
 _kmalloc_node_noprof include/linux/slab.h:1196 [inline]
 __get_vm_area_node+0x155/0x2f0 mm/vmalloc.c:3237
 __vmalloc_node_range_noprof+0x343/0x1540 mm/vmalloc.c:4064
 __vmalloc_node_noprof+0xc2/0x100 mm/vmalloc.c:4165
 alloc_thread_stack_node kernel/fork.c:359 [inline]
 dup_task_struct+0x2c6/0xa00 kernel/fork.c:930
 copy_process+0x7ea/0x44b0 kernel/fork.c:2143
 kernel_clone+0x2d7/0x940 kernel/fork.c:2785
 kernel_thread+0x13f/0x1b0 kernel/fork.c:2846
 create_kthread kernel/kthread.c:459 [inline]
 kthreadd+0x4ec/0x6e0 kernel/kthread.c:817
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
page last free pid 38 tgid 38 ts 9396138651 stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 __free_pages_prepare mm/page_alloc.c:1418 [inline]
 __free_frozen_pages+0xc93/0xd90 mm/page_alloc.c:2962
 __kasan_populate_vmalloc_do mm/kasan/shadow.c:393 [inline]
 __kasan_populate_vmalloc+0x1a8/0x1c0 mm/kasan/shadow.c:424
 kasan_populate_vmalloc include/linux/kasan.h:580 [inline]
 alloc_vmap_area+0xd10/0x1410 mm/vmalloc.c:2145
 __get_vm_area_node+0x200/0x2f0 mm/vmalloc.c:3248
 __vmalloc_node_range_noprof+0x343/0x1540 mm/vmalloc.c:4064
 __vmalloc_node_noprof+0xc2/0x100 mm/vmalloc.c:4165
 alloc_thread_stack_node kernel/fork.c:359 [inline]
 dup_task_struct+0x2c6/0xa00 kernel/fork.c:930
 copy_process+0x7ea/0x44b0 kernel/fork.c:2143
 kernel_clone+0x2d7/0x940 kernel/fork.c:2785
 user_mode_thread+0x115/0x180 kernel/fork.c:2862
 call_usermodehelper_exec_work+0x5c/0x230 kernel/umh.c:169
 process_one_work kernel/workqueue.c:3396 [inline]
 process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3479
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3560
 kthread+0x38b/0x480 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
 ffff8880340cc580: 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc
 ffff8880340cc600: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
>ffff8880340cc680: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
                            ^
 ffff8880340cc700: 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc
 ffff8880340cc780: 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc
==================================================================

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/22 03:40 upstream 4df4d2a577db 4ba27f85 .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Read in pool_ctr
2026/10/22 03:05 upstream 4df4d2a577db 4ba27f85 .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Read in pool_ctr
2026/10/22 02:32 upstream 4df4d2a577db 4ba27f85 .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Read in pool_ctr
2026/10/22 01:57 upstream 4df4d2a577db 4ba27f85 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Read in pool_ctr
2026/10/22 04:32 linux-next 9a482184d910 61c200c7 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce KASAN: slab-use-after-free Read in pool_ctr
* Struck through repros no longer work on HEAD.