KASAN: use-after-free Write in config_item_put

Status: upstream: reported C repro on 2026/08/02 12:13
Bug presence: origin:lts
[Documentation on labels]
Reported-by: syzbot+9debb7cf73b48e32a8e5@syzkaller.appspotmail.com
First crash: 57d, last: 26d
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2026/09/23 lts (merge base) 7df67a479906 C [report] KASAN: use-after-free Write in config_item_get
2026/09/23 upstream (ToT) fe2ec83746e5 C Didn't crash
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-10 KASAN: use-after-free Write in config_item_put 22 syz, C 4 19d 60d 0/2 upstream: reported C repro on 2026/07/29 14:28
android-6-1 KASAN: use-after-free Write in config_item_put 22 syz, C 2 18h24m 39d 0/2 upstream: reported C repro on 2026/08/20 01:54
▶ ▼ Fix bisection attempts (1)
Created Duration User Patch Repo Result
2026/09/01 22:05 1h42m bisect fix android13-5.15-lts OK (0) job log log

Sample crash report:
R10: 00007ffebd69a88c R11: 0000000000000246 R12: 00007ffebd69a88c
R13: 00007ffebd69a8c0 R14: 00007ffebd69a8a0 R15: 0000000000000007
 </TASK>
---[ end trace 3a037ca40251f3d6 ]---
==================================================================
BUG: KASAN: use-after-free in instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
BUG: KASAN: use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:167 [inline]
BUG: KASAN: use-after-free in __refcount_sub_and_test include/linux/refcount.h:272 [inline]
BUG: KASAN: use-after-free in __refcount_dec_and_test include/linux/refcount.h:315 [inline]
BUG: KASAN: use-after-free in refcount_dec_and_test include/linux/refcount.h:333 [inline]
BUG: KASAN: use-after-free in kref_put include/linux/kref.h:64 [inline]
BUG: KASAN: use-after-free in config_item_put+0x33/0x210 fs/configfs/item.c:149
Write of size 4 at addr ffff88810b331c24 by task syz-executor280/345

CPU: 0 PID: 345 Comm: syz-executor280 Tainted: G        W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 __dump_stack+0x21/0x30 lib/dump_stack.c:88
 dump_stack_lvl+0x110/0x170 lib/dump_stack.c:106
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:427 [inline]
 kasan_report+0x10f/0x150 mm/kasan/report.c:444
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x249/0x2a0 mm/kasan/generic.c:189
 __kasan_check_write+0x14/0x20 mm/kasan/shadow.c:37
 instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:167 [inline]
 __refcount_sub_and_test include/linux/refcount.h:272 [inline]
 __refcount_dec_and_test include/linux/refcount.h:315 [inline]
 refcount_dec_and_test include/linux/refcount.h:333 [inline]
 kref_put include/linux/kref.h:64 [inline]
 config_item_put+0x33/0x210 fs/configfs/item.c:149
 configfs_symlink+0x4a6/0x1330 fs/configfs/symlink.c:212
 vfs_symlink+0x29e/0x470 fs/namei.c:4437
 do_symlinkat+0x24a/0x5d0 fs/namei.c:4466
 __do_sys_symlinkat fs/namei.c:4483 [inline]
 __se_sys_symlinkat fs/namei.c:4480 [inline]
 __x64_sys_symlinkat+0x99/0xb0 fs/namei.c:4480
 x64_sys_call+0x74b/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:267
 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
RIP: 0033:0x7efd570a5429
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 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 d8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffebd69a858 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 00000000000062ce RCX: 00007efd570a5429
RDX: 0000200000000300 RSI: 00000000ffffff9c RDI: 0000200000000200
RBP: 0000000000000000 R08: 00007ffebd69a88c R09: 00007ffebd69a88c
R10: 00007ffebd69a88c R11: 0000000000000246 R12: 00007ffebd69a88c
R13: 00007ffebd69a8c0 R14: 00007ffebd69a8a0 R15: 0000000000000007
 </TASK>

Allocated by task 342:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:45 [inline]
 set_alloc_info mm/kasan/common.c:433 [inline]
 ____kasan_kmalloc mm/kasan/common.c:512 [inline]
 __kasan_kmalloc+0xd4/0x100 mm/kasan/common.c:521
 kasan_kmalloc include/linux/kasan.h:227 [inline]
 kmem_cache_alloc_trace+0x119/0x270 mm/slub.c:3274
 kmalloc include/linux/slab.h:619 [inline]
 kzalloc include/linux/slab.h:750 [inline]
 fsg_alloc_inst+0x61/0x5a0 drivers/usb/gadget/function/f_mass_storage.c:3392
 try_get_usb_function_instance drivers/usb/gadget/functions.c:28 [inline]
 usb_get_function_instance+0xe2/0x2f0 drivers/usb/gadget/functions.c:44
 function_make+0x118/0x350 drivers/usb/gadget/configfs.c:642
 configfs_mkdir+0x50a/0x9c0 fs/configfs/dir.c:1329
 vfs_mkdir+0x38b/0x590 fs/namei.c:4073
 do_mkdirat+0x174/0x4d0 fs/namei.c:4098
 __do_sys_mkdirat fs/namei.c:4113 [inline]
 __se_sys_mkdirat fs/namei.c:4111 [inline]
 __x64_sys_mkdirat+0x89/0xa0 fs/namei.c:4111
 x64_sys_call+0x37e/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:259
 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 344:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4a/0x70 mm/kasan/common.c:45
 kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:370
 ____kasan_slab_free+0x125/0x160 mm/kasan/common.c:365
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:373
 kasan_slab_free include/linux/kasan.h:193 [inline]
 slab_free_hook mm/slub.c:1728 [inline]
 slab_free_freelist_hook+0xc2/0x190 mm/slub.c:1754
 slab_free mm/slub.c:3526 [inline]
 kfree+0xc4/0x270 mm/slub.c:4588
 fsg_free_inst+0x33c/0x420 drivers/usb/gadget/function/f_mass_storage.c:3383
 usb_put_function_instance+0x85/0xa0 drivers/usb/gadget/functions.c:77
 fsg_attr_release+0x15/0x20 drivers/usb/gadget/function/f_mass_storage.c:3269
 config_item_cleanup fs/configfs/item.c:128 [inline]
 config_item_release fs/configfs/item.c:137 [inline]
 kref_put include/linux/kref.h:65 [inline]
 config_item_put+0x158/0x210 fs/configfs/item.c:149
 configfs_rmdir+0x89f/0x960 fs/configfs/dir.c:1540
 vfs_rmdir+0x1ae/0x450 fs/namei.c:4157
 do_rmdir+0x261/0x6b0 fs/namei.c:4218
 __do_sys_rmdir fs/namei.c:4237 [inline]
 __se_sys_rmdir fs/namei.c:4235 [inline]
 __x64_sys_rmdir+0x49/0x50 fs/namei.c:4235
 x64_sys_call+0x25f/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:85
 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

The buggy address belongs to the object at ffff88810b331c00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 36 bytes inside of
 512-byte region [ffff88810b331c00, ffff88810b331e00)
The buggy address belongs to the page:
page:ffffea00042ccc00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10b330
head:ffffea00042ccc00 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea00042cbe00 0000000200000002 ffff888100042f00
raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, ts 3038931514, free_ts 2915566835
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x192/0x1b0 mm/page_alloc.c:2607
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2613
 get_page_from_freelist+0x2c3a/0x2cd0 mm/page_alloc.c:4487
 __alloc_pages+0x1a2/0x460 mm/page_alloc.c:5824
 alloc_slab_page mm/slub.c:-1 [inline]
 allocate_slab mm/slub.c:1937 [inline]
 new_slab+0xa0/0x4d0 mm/slub.c:2000
 ___slab_alloc+0x3ac/0x840 mm/slub.c:3033
 __slab_alloc+0x49/0x90 mm/slub.c:3120
 slab_alloc_node mm/slub.c:3211 [inline]
 slab_alloc mm/slub.c:3255 [inline]
 kmem_cache_alloc_trace+0x146/0x270 mm/slub.c:3272
 kmalloc include/linux/slab.h:619 [inline]
 kzalloc include/linux/slab.h:750 [inline]
 dev_pm_qos_constraints_allocate+0x53/0x3f0 drivers/base/power/qos.c:201
 __dev_pm_qos_add_request+0x132/0x3e0 drivers/base/power/qos.c:345
 dev_pm_qos_add_request+0x37/0x50 drivers/base/power/qos.c:395
 usb_hub_create_port_device+0x459/0xad0 drivers/usb/core/port.c:602
 hub_configure drivers/usb/core/hub.c:1696 [inline]
 hub_probe+0x1f7d/0x2ad0 drivers/usb/core/hub.c:1952
 usb_probe_interface+0x60f/0xb20 drivers/usb/core/driver.c:396
 call_driver_probe drivers/base/dd.c:-1 [inline]
 really_probe+0x27d/0x970 drivers/base/dd.c:595
 __driver_probe_device+0x193/0x270 drivers/base/dd.c:755
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 free_pages_prepare mm/page_alloc.c:1474 [inline]
 free_pcp_prepare mm/page_alloc.c:1546 [inline]
 free_unref_page_prepare+0x5fa/0x600 mm/page_alloc.c:3536
 free_unref_page+0xae/0x540 mm/page_alloc.c:3618
 free_the_page mm/page_alloc.c:805 [inline]
 __free_pages+0x6c/0x100 mm/page_alloc.c:5900
 free_pages+0x82/0x90 mm/page_alloc.c:5911
 __stack_depot_save+0x453/0x480 lib/stackdepot.c:358
 kasan_save_stack mm/kasan/common.c:39 [inline]
 kasan_set_track+0x5b/0x70 mm/kasan/common.c:45
 kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:370
 ____kasan_slab_free+0x125/0x160 mm/kasan/common.c:365
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:373
 kasan_slab_free include/linux/kasan.h:193 [inline]
 slab_free_hook mm/slub.c:1728 [inline]
 slab_free_freelist_hook+0xc2/0x190 mm/slub.c:1754
 slab_free mm/slub.c:3526 [inline]
 kfree+0xc4/0x270 mm/slub.c:4588
 kobject_uevent_env+0x343/0x700 lib/kobject_uevent.c:640
 kobject_uevent+0x1d/0x30 lib/kobject_uevent.c:657
 driver_register+0x3ef/0x440 drivers/base/driver.c:248
 usb_register_driver+0x1f7/0x3e0 drivers/usb/core/driver.c:1061
 wdm_driver_init+0x1e/0x20 drivers/usb/class/cdc-wdm.c:1375

Memory state around the buggy address:
 ffff88810b331b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88810b331b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88810b331c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff88810b331c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88810b331d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 345 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 0 PID: 345 Comm: syz-executor280 Tainted: G    B   W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Code: 04 01 48 c7 c7 c0 46 63 85 e8 ac 47 5a 02 0f 0b eb c3 e8 43 80 19 ff c6 05 00 ea 95 04 01 48 c7 c7 20 47 63 85 e8 90 47 5a 02 <0f> 0b eb a7 e8 27 80 19 ff c6 05 e1 e9 95 04 01 48 c7 c7 60 46 63
RSP: 0018:ffffc90000c17c38 EFLAGS: 00010246
RAX: dde133087ed16300 RBX: 0000000000000003 RCX: ffff88810bf013c0
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc90000c17c48 R08: ffff8881f7032f3f R09: 1ffff1103ee065e7
R10: dffffc0000000000 R11: ffffed103ee065e8 R12: 00000000ffffffea
R13: dffffc0000000000 R14: 0000000000000003 R15: 00000000c0000000
FS:  000055558b467480(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055558b478858 CR3: 0000000122a2c000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 __refcount_sub_and_test include/linux/refcount.h:283 [inline]
 __refcount_dec_and_test include/linux/refcount.h:315 [inline]
 refcount_dec_and_test include/linux/refcount.h:333 [inline]
 kref_put include/linux/kref.h:64 [inline]
 config_item_put+0x200/0x210 fs/configfs/item.c:149
 configfs_symlink+0x4a6/0x1330 fs/configfs/symlink.c:212
 vfs_symlink+0x29e/0x470 fs/namei.c:4437
 do_symlinkat+0x24a/0x5d0 fs/namei.c:4466
 __do_sys_symlinkat fs/namei.c:4483 [inline]
 __se_sys_symlinkat fs/namei.c:4480 [inline]
 __x64_sys_symlinkat+0x99/0xb0 fs/namei.c:4480
 x64_sys_call+0x74b/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:267
 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
RIP: 0033:0x7efd570a5429
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 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 d8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffebd69a858 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 00000000000062ce RCX: 00007efd570a5429
RDX: 0000200000000300 RSI: 00000000ffffff9c RDI: 0000200000000200
RBP: 0000000000000000 R08: 00007ffebd69a88c R09: 00007ffebd69a88c
R10: 00007ffebd69a88c R11: 0000000000000246 R12: 00007ffebd69a88c
R13: 00007ffebd69a8c0 R14: 00007ffebd69a8a0 R15: 0000000000000007
 </TASK>
---[ end trace 3a037ca40251f3d7 ]---

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/02 12:12 android13-5.15-lts 61d896ee2a80 e611ffe1 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Write in config_item_put
* Struck through repros no longer work on HEAD.