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

Status: upstream: reported C repro on 2026/10/26 07:45
Reported-by: syzbot+a62287faa41696302099@syzkaller.appspotmail.com
First crash: 2d22h, last: 2d20h
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: slab-use-after-free Read in snapshot_ctr prio:normal dm 19 syz, C 170 now 4d14h 0/29 upstream: reported C repro on 2026/10/24 15:49
android-6-12 KASAN: slab-use-after-free Read in snapshot_ctr origin:upstream 19 syz, C 55 27m 8d09h 0/1 premoderation: reported C repro on 2026/10/20 20:44

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in snapshot_ctr+0x5cc/0x1340 drivers/md/dm-snap.c:1288
Read of size 8 at addr ffff88802aa87b98 by task syz.0.17/5963

CPU: 1 PID: 5963 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:364 [inline]
 print_report+0xa8/0x210 mm/kasan/report.c:468
 kasan_report+0x117/0x150 mm/kasan/report.c:581
 snapshot_ctr+0x5cc/0x1340 drivers/md/dm-snap.c:1288
 dm_table_add_target+0x575/0xbc0 drivers/md/dm-table.c:732
 populate_table drivers/md/dm-ioctl.c:1502 [inline]
 table_load+0x2eb/0x7e0 drivers/md/dm-ioctl.c:1544
 ctl_ioctl drivers/md/dm-ioctl.c:2115 [inline]
 dm_ctl_ioctl+0x975/0xd00 drivers/md/dm-ioctl.c:2137
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fd760f9f559
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:00007fff84c030a8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fd761225fa0 RCX: 00007fd760f9f559
RDX: 0000200000000500 RSI: 00000000c138fd09 RDI: 0000000000000003
RBP: 00007fd761036b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd761225fac R14: 00007fd761225fa0 R15: 00007fd761225fa0
 </TASK>

Allocated by task 5963:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
 ____kasan_kmalloc mm/kasan/common.c:375 [inline]
 __kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:384
 kmalloc_node include/linux/slab.h:616 [inline]
 open_table_device drivers/md/dm.c:731 [inline]
 dm_get_table_device+0x248/0x670 drivers/md/dm.c:800
 dm_get_device+0x4b9/0x9e0 drivers/md/dm-table.c:378
 snapshot_ctr+0x2b3/0x1340 drivers/md/dm-snap.c:1273
 dm_table_add_target+0x575/0xbc0 drivers/md/dm-table.c:732
 populate_table drivers/md/dm-ioctl.c:1502 [inline]
 table_load+0x2eb/0x7e0 drivers/md/dm-ioctl.c:1544
 ctl_ioctl drivers/md/dm-ioctl.c:2115 [inline]
 dm_ctl_ioctl+0x975/0xd00 drivers/md/dm-ioctl.c:2137
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Freed by task 5963:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
 kasan_save_free_info+0x28/0x40 mm/kasan/generic.c:522
 ____kasan_slab_free+0x126/0x1f0 mm/kasan/common.c:237
 kasan_slab_free include/linux/kasan.h:164 [inline]
 slab_free_hook mm/slub.c:1833 [inline]
 slab_free_freelist_hook+0x154/0x240 mm/slub.c:1859
 slab_free mm/slub.c:3853 [inline]
 __kmem_cache_free+0xba/0x1f0 mm/slub.c:3866
 close_table_device drivers/md/dm.c:777 [inline]
 dm_put_table_device+0x20e/0x240 drivers/md/dm.c:820
 upgrade_mode drivers/md/dm-table.c:327 [inline]
 dm_get_device+0x7ca/0x9e0 drivers/md/dm-table.c:389
 snapshot_ctr+0x472/0x1340 drivers/md/dm-snap.c:1283
 dm_table_add_target+0x575/0xbc0 drivers/md/dm-table.c:732
 populate_table drivers/md/dm-ioctl.c:1502 [inline]
 table_load+0x2eb/0x7e0 drivers/md/dm-ioctl.c:1544
 ctl_ioctl drivers/md/dm-ioctl.c:2115 [inline]
 dm_ctl_ioctl+0x975/0xd00 drivers/md/dm-ioctl.c:2137
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff88802aa87b80
 which belongs to the cache kmalloc-64 of size 64
The buggy address is located 24 bytes inside of
 freed 64-byte region [ffff88802aa87b80, ffff88802aa87bc0)

The buggy address belongs to the physical page:
page:ffffea0000aaa1c0 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2aa87
anon flags: 0xfff00000000800(slab|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000800 ffff888018c41640 ffffea00006fe480 dead000000000005
raw: 0000000000000000 0000000080200020 00000001ffffffff 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 0x12cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY), pid 1, tgid 1 (swapper/0), ts 18142952831, free_ts 0
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x1c1/0x200 mm/page_alloc.c:1582
 prep_new_page mm/page_alloc.c:1589 [inline]
 get_page_from_freelist+0x2181/0x22a0 mm/page_alloc.c:3221
 __alloc_pages+0x1f0/0x460 mm/page_alloc.c:4501
 alloc_page_interleave+0x24/0x1e0 mm/mempolicy.c:2118
 alloc_slab_page+0x5d/0x180 mm/slub.c:1903
 allocate_slab mm/slub.c:2050 [inline]
 new_slab+0x87/0x2d0 mm/slub.c:2103
 ___slab_alloc+0xc5c/0x12f0 mm/slub.c:3275
 __slab_alloc mm/slub.c:3361 [inline]
 __slab_alloc_node mm/slub.c:3414 [inline]
 slab_alloc_node mm/slub.c:3508 [inline]
 __kmem_cache_alloc_node+0x122/0x260 mm/slub.c:3557
 kmalloc_trace+0x2a/0xe0 mm/slab_common.c:1098
 kmalloc include/linux/slab.h:600 [inline]
 kzalloc include/linux/slab.h:721 [inline]
 media_devnode_create+0x60/0x380 drivers/media/mc/mc-entity.c:1537
 video_register_media_controller drivers/media/v4l2-core/v4l2-dev.c:851 [inline]
 __video_register_device+0x3e37/0x4780 drivers/media/v4l2-core/v4l2-dev.c:1056
 video_register_device include/media/v4l2-dev.h:383 [inline]
 vivid_create_devnodes+0x1124/0x2c20 drivers/media/test-drivers/vivid/vivid-core.c:1486
 vivid_create_instance drivers/media/test-drivers/vivid/vivid-core.c:1951 [inline]
 vivid_probe+0x4e28/0x6570 drivers/media/test-drivers/vivid/vivid-core.c:2004
 platform_probe+0x13b/0x1c0 drivers/base/platform.c:1376
 call_driver_probe drivers/base/dd.c:-1 [inline]
 really_probe+0x24a/0xae0 drivers/base/dd.c:717
 __driver_probe_device+0x1f5/0x390 drivers/base/dd.c:879
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88802aa87a80: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
 ffff88802aa87b00: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
>ffff88802aa87b80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                            ^
 ffff88802aa87c00: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
 ffff88802aa87c80: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/26 09:02 linux-6.6.y 0aebf2870d53 1d9ca40b .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in snapshot_ctr
2026/10/26 08:37 linux-6.6.y 0aebf2870d53 1d9ca40b .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in snapshot_ctr
2026/10/26 08:12 linux-6.6.y 0aebf2870d53 1d9ca40b .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in snapshot_ctr
2026/10/26 07:45 linux-6.6.y 0aebf2870d53 1d9ca40b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in snapshot_ctr
2026/10/26 07:45 linux-6.6.y 0aebf2870d53 1d9ca40b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in snapshot_ctr
* Struck through repros no longer work on HEAD.