KASAN: slab-use-after-free Read in txLazyUnlock (4)

Status: moderation: reported on 2026/08/29 03:33
Subsystems: jfs
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+518bb1aae8d477d7242a@syzkaller.appspotmail.com
First crash: 4d19h, last: 4d19h
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
065516f9 assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ✅ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KASAN: slab-use-after-free Read in txLazyUnlock (4) 2026/08/27 01:22 2026/08/27 01:22 2026/08/27 02:01 a2b77b9e
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: slab-use-after-free Read in txLazyUnlock (3) prio:high jfs 19 35 93d 93d 0/29 auto-obsoleted due to no activity on 2026/08/06 10:30
upstream KASAN: slab-use-after-free Read in txLazyUnlock (2) jfs 19 4 353d 371d 0/29 auto-obsoleted due to no activity on 2025/12/09 19:50
upstream KASAN: slab-use-after-free Read in txLazyUnlock jfs 19 1 605d 601d 0/29 auto-obsoleted due to no activity on 2025/04/01 16:48

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in JFS_SBI fs/jfs/jfs_incore.h:217 [inline]
BUG: KASAN: slab-use-after-free in txLazyUnlock+0xf6/0x190 fs/jfs/jfs_txnmgr.c:2786
Read of size 8 at addr ffff88803d06e828 by task kworker/u8:2/40

CPU: 1 UID: 0 PID: 40 Comm: kworker/u8:2 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: writeback wb_workfn (flush-7:7)
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
 JFS_SBI fs/jfs/jfs_incore.h:217 [inline]
 txLazyUnlock+0xf6/0x190 fs/jfs/jfs_txnmgr.c:2786
 lmPostGC fs/jfs/jfs_logmgr.c:843 [inline]
 lbmIODone+0x95f/0x16b0 fs/jfs/jfs_logmgr.c:2283
 lbmWrite+0x34e/0x4a0 fs/jfs/jfs_logmgr.c:2064
 lmGCwrite fs/jfs/jfs_logmgr.c:-1 [inline]
 jfs_flush_journal+0x548/0xf50 fs/jfs/jfs_logmgr.c:1545
 metapage_write_folio+0x3cf/0xd40 fs/jfs/jfs_metapage.c:463
 metapage_writepages+0xe8/0x1a0 fs/jfs/jfs_metapage.c:559
 do_writepages+0x338/0x560 mm/page-writeback.c:2560
 __writeback_single_inode+0x136/0x1230 fs/fs-writeback.c:1788
 writeback_sb_inodes+0x9db/0x1ab0 fs/fs-writeback.c:2099
 wb_writeback+0x41c/0xad0 fs/fs-writeback.c:2284
 wb_do_writeback fs/fs-writeback.c:2452 [inline]
 wb_workfn+0x437/0x10f0 fs/fs-writeback.c:2497
 process_one_work kernel/workqueue.c:3387 [inline]
 process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3470
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3551
 kthread+0x38b/0x470 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
 </TASK>

Allocated by task 1442:
 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:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __do_kmalloc_node mm/slub.c:5337 [inline]
 __kmalloc_node_track_caller_noprof+0x587/0x7d0 mm/slub.c:5466
 kmalloc_reserve net/core/skbuff.c:637 [inline]
 __alloc_skb+0x2c1/0x7a0 net/core/skbuff.c:715
 alloc_skb include/linux/skbuff.h:1384 [inline]
 nsim_dev_trap_skb_build drivers/net/netdevsim/dev.c:744 [inline]
 nsim_dev_trap_report drivers/net/netdevsim/dev.c:801 [inline]
 nsim_dev_trap_report_work+0x2b1/0xcb0 drivers/net/netdevsim/dev.c:847
 process_one_work kernel/workqueue.c:3387 [inline]
 process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3470
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3551
 kthread+0x38b/0x470 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

Freed by task 1442:
 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:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2678 [inline]
 slab_free mm/slub.c:6372 [inline]
 kfree+0x1c5/0x6d0 mm/slub.c:6687
 skb_kfree_head net/core/skbuff.c:1083 [inline]
 skb_free_head net/core/skbuff.c:1095 [inline]
 skb_release_data+0x85e/0xab0 net/core/skbuff.c:1122
 skb_release_all net/core/skbuff.c:1197 [inline]
 __kfree_skb+0x5d/0x210 net/core/skbuff.c:1211
 nsim_dev_trap_report drivers/net/netdevsim/dev.c:817 [inline]
 nsim_dev_trap_report_work+0x879/0xcb0 drivers/net/netdevsim/dev.c:847
 process_one_work kernel/workqueue.c:3387 [inline]
 process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3470
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3551
 kthread+0x38b/0x470 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

The buggy address belongs to the object at ffff88803d06e000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 2088 bytes inside of
 freed 4096-byte region [ffff88803d06e000, ffff88803d06f000)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x3d068
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0x80000000000040(head|node=0|zone=1)
page_type: f5(slab)
raw: 0080000000000040 ffff88813ffbd140 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800040004 00000000f5000000 0000000000000000
head: 0080000000000040 ffff88813ffbd140 dead000000000100 dead000000000122
head: 0000000000000000 0000000800040004 00000000f5000000 0000000000000000
head: 0080000000000003 fffffffffffffe01 00000000ffffffff 00000000ffffffff
head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 4967, tgid 4967 (udevd), ts 53171553169
 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+0x2591/0x2600 mm/page_alloc.c:3943
 __alloc_frozen_pages_noprof+0x230/0x5c0 mm/page_alloc.c:5436
 alloc_slab_page mm/slub.c:3267 [inline]
 allocate_slab+0x7c/0x5e0 mm/slub.c:3382
 new_slab mm/slub.c:3428 [inline]
 refill_objects+0x2d8/0x350 mm/slub.c:7305
 refill_sheaf mm/slub.c:2805 [inline]
 __pcs_replace_empty_main+0x334/0x690 mm/slub.c:4677
 alloc_from_pcs mm/slub.c:4775 [inline]
 slab_alloc_node mm/slub.c:4907 [inline]
 __do_kmalloc_node mm/slub.c:5336 [inline]
 __kmalloc_noprof+0x54c/0x780 mm/slub.c:5362
 _kmalloc_noprof include/linux/slab.h:992 [inline]
 tomoyo_realpath_from_path+0xef/0x640 security/tomoyo/realpath.c:251
 tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
 tomoyo_path_number_perm+0x246/0x5f0 security/tomoyo/file.c:728
 security_path_chown+0x139/0x340 security/security.c:1598
 chown_common+0x3c0/0x640 fs/open.c:820
 do_fchownat+0x14c/0x250 fs/open.c:853
 __do_sys_chown fs/open.c:873 [inline]
 __se_sys_chown fs/open.c:871 [inline]
 __x64_sys_chown+0x82/0xa0 fs/open.c:871
 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
page last free pid 4970 tgid 4970 ts 53097550260 stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 __free_pages_prepare mm/page_alloc.c:1418 [inline]
 __free_frozen_pages+0xf8e/0x1070 mm/page_alloc.c:2962
 __slab_free+0x252/0x2a0 mm/slub.c:5736
 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:350
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4586 [inline]
 slab_alloc_node mm/slub.c:4919 [inline]
 kmem_cache_alloc_noprof+0x35d/0x660 mm/slub.c:4933
 alloc_filename fs/namei.c:147 [inline]
 do_getname+0x2e/0x250 fs/namei.c:187
 class_filename_flags_constructor include/linux/fs.h:2587 [inline]
 do_sys_openat2+0xcc/0x200 fs/open.c:1416
 do_sys_open fs/open.c:1423 [inline]
 __do_sys_openat fs/open.c:1439 [inline]
 __se_sys_openat fs/open.c:1434 [inline]
 __x64_sys_openat+0x138/0x170 fs/open.c:1434
 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:
 ffff88803d06e700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88803d06e780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88803d06e800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                  ^
 ffff88803d06e880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88803d06e900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/25 03:23 upstream 0a0d1d55dad5 614e416a .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs KASAN: slab-use-after-free Read in txLazyUnlock
* Struck through repros no longer work on HEAD.