KASAN: use-after-free Read in trylock_super (2)

Status: upstream: reported on 2026/11/09 15:10
Reported-by: syzbot+0b166f301028c27bdff7@syzkaller.appspotmail.com
First crash: 5d14h, last: 5d14h
▶ ▼ Similar bugs (6)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 KASAN: use-after-free Read in trylock_super 19 1 282d 282d 0/3 auto-obsoleted due to no activity on 2026/05/16 06:22
android-5-15 KASAN: use-after-free Write in trylock_super vfs origin:lts missing-backport 22 syz error 114 19d 1439d 0/2 premoderation: reported syz repro on 2022/12/07 03:02
linux-5.15 KASAN: use-after-free Read in trylock_super 19 1 687d 687d 0/3 auto-obsoleted due to no activity on 2025/04/06 15:01
upstream KASAN: slab-use-after-free Read in trylock_super fs 19 1 1323d 1319d 0/29 auto-obsoleted due to no activity on 2023/07/01 04:40
android-54 KASAN: use-after-free Write in trylock_super 22 4 1252d 1341d 0/2 auto-obsoleted due to no activity on 2023/09/19 19:51
android-5-10 KASAN: use-after-free Write in trylock_super vfs 22 syz inconclusive 120 16d 1445d 0/2 premoderation: reported syz repro on 2022/11/30 20:27

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in __down_read_trylock kernel/locking/rwsem.c:1270 [inline]
BUG: KASAN: use-after-free in down_read_trylock+0xaf/0x3b0 kernel/locking/rwsem.c:1537
Read of size 8 at addr ffff8880749ec0d8 by task kworker/u4:0/12706

CPU: 0 PID: 12706 Comm: kworker/u4:0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/06/2026
Workqueue: writeback wb_workfn (flush-7:9)
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 print_address_description+0x60/0x2d0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:434 [inline]
 kasan_report+0xdf/0x130 mm/kasan/report.c:451
 __down_read_trylock kernel/locking/rwsem.c:1270 [inline]
 down_read_trylock+0xaf/0x3b0 kernel/locking/rwsem.c:1537
 trylock_super+0x1c/0xf0 fs/super.c:418
 __writeback_inodes_wb+0x114/0x3f0 fs/fs-writeback.c:2002
 wb_writeback+0x45e/0xbc0 fs/fs-writeback.c:2116
 wb_check_background_flush fs/fs-writeback.c:2182 [inline]
 wb_do_writeback fs/fs-writeback.c:2270 [inline]
 wb_workfn+0xbd6/0xf20 fs/fs-writeback.c:2298
 process_one_work+0x867/0xff0 kernel/workqueue.c:2310
 worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>

Allocated by task 14820:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:434 [inline]
 ____kasan_kmalloc mm/kasan/common.c:513 [inline]
 __kasan_kmalloc+0xaf/0xe0 mm/kasan/common.c:522
 kmalloc include/linux/slab.h:607 [inline]
 kzalloc include/linux/slab.h:738 [inline]
 alloc_super+0x59/0x970 fs/super.c:203
 sget+0x1ce/0x450 fs/super.c:637
 nilfs_mount+0x452/0x8c0 fs/nilfs2/super.c:1331
 legacy_get_tree+0xe6/0x180 fs/fs_context.c:611
 vfs_get_tree+0x88/0x270 fs/super.c:1541
 do_new_mount+0x247/0xa50 fs/namespace.c:3060
 do_mount fs/namespace.c:3431 [inline]
 __do_sys_mount fs/namespace.c:3639 [inline]
 __se_sys_mount+0x2e3/0x3d0 fs/namespace.c:3616
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

Freed by task 4363:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:46
 kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:360
 ____kasan_slab_free+0xd5/0x110 mm/kasan/common.c:366
 kasan_slab_free include/linux/kasan.h:230 [inline]
 slab_free_hook mm/slub.c:1710 [inline]
 slab_free_freelist_hook+0xec/0x170 mm/slub.c:1736
 slab_free mm/slub.c:3504 [inline]
 kfree+0xef/0x2a0 mm/slub.c:4564
 process_one_work+0x867/0xff0 kernel/workqueue.c:2310
 worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

Last potentially related work creation:
 kasan_save_stack+0x35/0x60 mm/kasan/common.c:38
 kasan_record_aux_stack+0xb8/0x100 mm/kasan/generic.c:348
 insert_work+0x54/0x3d0 kernel/workqueue.c:1366
 __queue_work+0x90b/0xc80 kernel/workqueue.c:1532
 queue_work_on+0x124/0x1f0 kernel/workqueue.c:1559
 rcu_do_batch kernel/rcu/tree.c:2523 [inline]
 rcu_core+0x96e/0x1650 kernel/rcu/tree.c:2763
 handle_softirqs+0x336/0x830 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676

Second to last potentially related work creation:
 kasan_save_stack+0x35/0x60 mm/kasan/common.c:38
 kasan_record_aux_stack+0xb8/0x100 mm/kasan/generic.c:348
 __call_rcu kernel/rcu/tree.c:3011 [inline]
 call_rcu+0x189/0x900 kernel/rcu/tree.c:3091
 put_super fs/super.c:313 [inline]
 deactivate_locked_super+0xc7/0xf0 fs/super.c:346
 cleanup_mnt+0x426/0x4d0 fs/namespace.c:1148
 task_work_run+0x125/0x1a0 kernel/task_work.c:188
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop+0x10f/0x130 kernel/entry/common.c:184
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:217
 __syscall_exit_to_user_mode_work kernel/entry/common.c:299 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:310
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

The buggy address belongs to the object at ffff8880749ec000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 216 bytes inside of
 4096-byte region [ffff8880749ec000, ffff8880749ed000)
The buggy address belongs to the page:
page:ffffea0001d27a00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x749e8
head:ffffea0001d27a00 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 0000000100000001 ffff888017842140
raw: 0000000000000000 0000000000040004 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x1d2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 4194, ts 68592766799, free_ts 68560499978
 prep_new_page mm/page_alloc.c:2426 [inline]
 get_page_from_freelist+0x24f6/0x2670 mm/page_alloc.c:4192
 __alloc_pages+0x1ee/0x480 mm/page_alloc.c:5501
 alloc_slab_page mm/slub.c:1780 [inline]
 allocate_slab mm/slub.c:1917 [inline]
 new_slab+0xc0/0x4b0 mm/slub.c:1980
 ___slab_alloc+0x807/0xdd0 mm/slub.c:3013
 __slab_alloc mm/slub.c:3100 [inline]
 slab_alloc_node mm/slub.c:3191 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 __kmalloc+0x11d/0x340 mm/slub.c:4408
 kmalloc include/linux/slab.h:612 [inline]
 tomoyo_realpath_from_path+0xed/0x5e0 security/tomoyo/realpath.c:254
 tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
 tomoyo_path_number_perm+0x251/0x6b0 security/tomoyo/file.c:723
 tomoyo_path_mkdir+0xad/0xf0 security/tomoyo/tomoyo.c:166
 security_path_mkdir+0xe0/0x130 security/security.c:1205
 do_mkdirat+0x15e/0x5c0 fs/namei.c:4136
 __do_sys_mkdirat fs/namei.c:4156 [inline]
 __se_sys_mkdirat fs/namei.c:4154 [inline]
 __x64_sys_mkdirat+0x85/0x90 fs/namei.c:4154
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1340 [inline]
 free_pcp_prepare mm/page_alloc.c:1391 [inline]
 free_unref_page_prepare+0x637/0x6c0 mm/page_alloc.c:3317
 free_unref_page+0x8f/0x2a0 mm/page_alloc.c:3396
 free_slab mm/slub.c:2020 [inline]
 discard_slab mm/slub.c:2026 [inline]
 __unfreeze_partials+0x188/0x1e0 mm/slub.c:2512
 put_cpu_partial+0x12d/0x190 mm/slub.c:2592
 qlist_free_all+0x35/0x90 mm/kasan/quarantine.c:176
 kasan_quarantine_reduce+0x150/0x160 mm/kasan/quarantine.c:283
 __kasan_slab_alloc+0x2f/0xc0 mm/kasan/common.c:444
 kasan_slab_alloc include/linux/kasan.h:254 [inline]
 slab_post_alloc_hook+0x4c/0x380 mm/slab.h:519
 slab_alloc_node mm/slub.c:3225 [inline]
 kmem_cache_alloc_node+0x184/0x2c0 mm/slub.c:3261
 __alloc_skb+0xf4/0x750 net/core/skbuff.c:415
 alloc_skb include/linux/skbuff.h:1162 [inline]
 mld_newpack+0x12f/0xba0 net/ipv6/mcast.c:1773
 add_grhead net/ipv6/mcast.c:1884 [inline]
 add_grec+0x1364/0x1840 net/ipv6/mcast.c:2023
 mld_send_cr net/ipv6/mcast.c:2146 [inline]
 mld_ifc_work+0x6f2/0xd60 net/ipv6/mcast.c:2688
 process_one_work+0x867/0xff0 kernel/workqueue.c:2310
 worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
 kthread+0x42e/0x520 kernel/kthread.c:334

Memory state around the buggy address:
 ffff8880749ebf80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880749ec000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880749ec080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                    ^
 ffff8880749ec100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880749ec180: 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
2026/11/09 15:09 linux-5.15.y 29c6cdaac04a 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in trylock_super
* Struck through repros no longer work on HEAD.