[syzbot] [dm?] KASAN: slab-use-after-free Read in snapshot_ctr

[syzbot] [dm?] KASAN: slab-use-after-free Read in snapshot_ctr

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    f47d223627f8 Merge tag 'vfs-7.4-rc1.sync_close' of git://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=127202a5580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=97e47414c855a3d8
dashboard link: https://syzkaller.appspot.com/bug?extid=8e6fc64255334ccf3ab3
compiler:       Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16a47f71580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13edba35580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-f47d2236.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a94d6307dbbf/vmlinux-f47d2236.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f114012b9c35/bzImage-f47d2236.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8e6fc64255334ccf3ab3@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in snapshot_ctr+0x5cb/0x1340 drivers/md/dm-snap.c:1282
Read of size 8 at addr ffff888038e19518 by task syz.0.17/5512

CPU: 0 UID: 0 PID: 5512 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
 snapshot_ctr+0x5cb/0x1340 drivers/md/dm-snap.c:1282
 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: 0033:0x7f239a99f559
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:00007ffdb38c50f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f239ac25fa0 RCX: 00007f239a99f559
RDX: 0000200000001640 RSI: 00000000c138fd09 RDI: 0000000000000003
RBP: 00007f239aa36b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f239ac25fac R14: 00007f239ac25fa0 R15: 00007f239ac25fa0
 </TASK>

Allocated by task 5512:
 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+0x3d1/0x620 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/0x740 drivers/md/dm.c:821
 dm_get_device+0x327/0x760 drivers/md/dm-table.c:388
 snapshot_ctr+0x2b2/0x1340 drivers/md/dm-snap.c:1267
 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 5512:
 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
 snapshot_ctr+0x471/0x1340 drivers/md/dm-snap.c:1277
 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 ffff888038e19500
 which belongs to the cache kmalloc-96 of size 96
The buggy address is located 24 bytes inside of
 freed 96-byte region [ffff888038e19500, ffff888038e19560)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x38e19
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 195, tgid 195 (kworker/u4:7), ts 22161879156
 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]
 __do_kmalloc_node mm/slub.c:5413 [inline]
 __kmalloc_noprof+0x47b/0x720 mm/slub.c:5439
 _kmalloc_noprof include/linux/slab.h:995 [inline]
 _kzalloc_noprof include/linux/slab.h:1312 [inline]
 lsm_blob_alloc security/security.c:218 [inline]
 lsm_task_alloc security/security.c:270 [inline]
 security_task_alloc+0x4d/0x330 security/security.c:2785
 copy_process+0x1c7a/0x44b0 kernel/fork.c:2301
 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
page last free pid 195 tgid 195 ts 22161737366 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
 ___free_pages_bulk mm/kasan/shadow.c:333 [inline]
 __kasan_populate_vmalloc_do mm/kasan/shadow.c:385 [inline]
 __kasan_populate_vmalloc+0x12d/0x1c0 mm/kasan/shadow.c:424
 kasan_populate_vmalloc include/linux/kasan.h:580 [inline]
 alloc_vmap_area+0xd1a/0x1420 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+0x7ef/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:
 ffff888038e19400: 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc
 ffff888038e19480: 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc
>ffff888038e19500: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
                            ^
 ffff888038e19580: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
 ffff888038e19600: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
==================================================================


---
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If you want syzbot to run the reproducer, reply with:
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Re: [syzbot] [dm?] KASAN: slab-use-after-free Read in snapshot_ctr

[Hillf Danton]

> Date: Sat, 24 Oct 2026 08:49:41 -0700	[thread overview]
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    f47d223627f8 Merge tag 'vfs-7.4-rc1.sync_close' of git://g..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=127202a5580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=97e47414c855a3d8
> dashboard link: https://syzkaller.appspot.com/bug?extid=8e6fc64255334ccf3ab3
> compiler:       Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16a47f71580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13edba35580000

#syz test: upstream  f47d223627f8

--- x/drivers/md/dm-table.c
+++ y/drivers/md/dm-table.c
@@ -400,8 +400,8 @@ int dm_get_device(struct dm_target *ti,
 		if (r)
 			return r;
 	}
-	refcount_inc(&dd->count);
 out:
+	refcount_inc(&dd->count);
 	*result = dd->dm_dev;
 	return 0;
 }
--- x/drivers/md/dm-snap.c
+++ y/drivers/md/dm-snap.c
@@ -1390,6 +1390,7 @@ static int snapshot_ctr(struct dm_target
 	if (r)
 		goto bad_read_metadata;
 
+	dm_put_device(ti, s->cow);
 	return 0;
 
 bad_read_metadata:
--

Re: [syzbot] [dm?] KASAN: slab-use-after-free Read in snapshot_ctr

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: slab-use-after-free Read in snapshot_ctr

==================================================================
BUG: KASAN: slab-use-after-free in snapshot_ctr+0x5cb/0x1370 drivers/md/dm-snap.c:1282
Read of size 8 at addr ffff88801388a898 by task syz.0.17/5914

CPU: 0 UID: 0 PID: 5914 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
 snapshot_ctr+0x5cb/0x1370 drivers/md/dm-snap.c:1282
 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: 0033:0x7f5604b9f559
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:00007f5605b42028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f5604e25fa0 RCX: 00007f5604b9f559
RDX: 0000200000001640 RSI: 00000000c138fd09 RDI: 0000000000000003
RBP: 00007f5604c36b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5604e26038 R14: 00007f5604e25fa0 R15: 00007ffe1ba2cfd8
 </TASK>

Allocated by task 5914:
 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+0x3d1/0x620 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/0x740 drivers/md/dm.c:821
 dm_get_device+0x327/0x750 drivers/md/dm-table.c:388
 snapshot_ctr+0x2b2/0x1370 drivers/md/dm-snap.c:1267
 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 5914:
 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+0x567/0x750 drivers/md/dm-table.c:399
 snapshot_ctr+0x471/0x1370 drivers/md/dm-snap.c:1277
 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 ffff88801388a880
 which belongs to the cache kmalloc-96 of size 96
The buggy address is located 24 bytes inside of
 freed 96-byte region [ffff88801388a880, ffff88801388a8e0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1388a
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 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 0x252800(GFP_NOWAIT|__GFP_NORETRY|__GFP_COMP|__GFP_THISNODE), pid 5850, tgid 5850 (syz-executor), ts 160176372736
 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_pages_slowpath+0x3f9/0xec0 mm/page_alloc.c:4884
 __alloc_frozen_pages_noprof+0x3f3/0x5a0 mm/page_alloc.c:5449
 alloc_slab_page mm/slub.c:3347 [inline]
 allocate_slab+0x7d/0x620 mm/slub.c:3462
 new_slab mm/slub.c:3513 [inline]
 ___slab_alloc+0x16a/0x960 mm/slub.c:4568
 slab_alloc_node mm/slub.c:4987 [inline]
 __kmalloc_cache_node_noprof+0x1db/0x620 mm/slub.c:5578
 _kmalloc_node_noprof include/linux/slab.h:1196 [inline]
 alloc_node_nr_active kernel/workqueue.c:5079 [inline]
 __alloc_workqueue+0x746/0x1fe0 kernel/workqueue.c:5974
 alloc_workqueue_va kernel/workqueue.c:6033 [inline]
 alloc_workqueue_noprof+0xe3/0x210 kernel/workqueue.c:6049
 ieee80211_register_hw+0x368f/0x4b00 net/mac80211/main.c:1523
 mac80211_hwsim_new_radio+0x3258/0x56b0 drivers/net/wireless/virtual/mac80211_hwsim_main.c:6143
 hwsim_new_radio_nl+0xd8b/0xf90 drivers/net/wireless/virtual/mac80211_hwsim_main.c:6966
 genl_family_rcv_msg_doit+0x233/0x340 net/netlink/genetlink.c:1114
 genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
 genl_rcv_msg+0x614/0x7a0 net/netlink/genetlink.c:1209
 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2579
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
page last free pid 5899 tgid 5899 ts 159580482965 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
 __slab_free+0x274/0x2c0 mm/slub.c:5823
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x99/0x100 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:361
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4683 [inline]
 slab_alloc_node mm/slub.c:4996 [inline]
 kmem_cache_alloc_noprof+0x2b9/0x600 mm/slub.c:5010
 vm_area_alloc+0x24/0x140 mm/vma_init.c:36
 __mmap_new_vma mm/vma.c:2671 [inline]
 __mmap_region mm/vma.c:2904 [inline]
 mmap_region+0x13d6/0x25b0 mm/vma.c:2989
 do_mmap+0xe0a/0x1300 mm/mmap.c:573
 vm_mmap_pgoff+0x272/0x4e0 mm/util.c:581
 ksys_mmap_pgoff+0x4dc/0x760 mm/mmap.c:619
 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

Memory state around the buggy address:
 ffff88801388a780: 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc
 ffff88801388a800: 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc
>ffff88801388a880: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
                            ^
 ffff88801388a900: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
 ffff88801388a980: 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc
==================================================================


Tested on:

commit:         f47d2236 Merge tag 'vfs-7.4-rc1.sync_close' of git://g..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1093470d580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=97e47414c855a3d8
dashboard link: https://syzkaller.appspot.com/bug?extid=8e6fc64255334ccf3ab3
compiler:       Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=12f7d931580000

Re: [syzbot] [dm?] KASAN: slab-use-after-free Read in snapshot_ctr

[Hillf Danton]

> Date: Sat, 24 Oct 2026 08:49:41 -0700	[thread overview]
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    f47d223627f8 Merge tag 'vfs-7.4-rc1.sync_close' of git://g..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=127202a5580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=97e47414c855a3d8
> dashboard link: https://syzkaller.appspot.com/bug?extid=8e6fc64255334ccf3ab3
> compiler:       Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16a47f71580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13edba35580000

#syz test: upstream  f47d223627f8

--- x/drivers/md/dm-table.c
+++ y/drivers/md/dm-table.c
@@ -400,8 +400,8 @@ int dm_get_device(struct dm_target *ti,
 		if (r)
 			return r;
 	}
-	refcount_inc(&dd->count);
 out:
+	refcount_inc(&dd->count);
 	*result = dd->dm_dev;
 	return 0;
 }
--- x/drivers/md/dm-snap.c
+++ y/drivers/md/dm-snap.c
@@ -1390,6 +1390,7 @@ static int snapshot_ctr(struct dm_target
 	if (r)
 		goto bad_read_metadata;
 
+	dm_put_device(ti, s->cow);
 	return 0;
 
 bad_read_metadata:
--- x/drivers/md/dm.c
+++ y/drivers/md/dm.c
@@ -823,9 +823,8 @@ int dm_get_table_device(struct mapped_de
 			mutex_unlock(&md->table_devices_lock);
 			return PTR_ERR(td);
 		}
-	} else {
-		refcount_inc(&td->count);
 	}
+	refcount_inc(&td->count);
 	mutex_unlock(&md->table_devices_lock);
 
 	*result = &td->dm_dev;
--

Re: [syzbot] [dm?] KASAN: slab-use-after-free Read in snapshot_ctr

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+8e6fc64255334ccf3ab3@syzkaller.appspotmail.com
Tested-by: syzbot+8e6fc64255334ccf3ab3@syzkaller.appspotmail.com

Tested on:

commit:         f47d2236 Merge tag 'vfs-7.4-rc1.sync_close' of git://g..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=15bc1459580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=97e47414c855a3d8
dashboard link: https://syzkaller.appspot.com/bug?extid=8e6fc64255334ccf3ab3
compiler:       Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1230d695580000

Note: testing is done by a robot and is best-effort only.