KASAN: use-after-free Write in config_item_put

Status: upstream: reported C repro on 2026/07/29 14:28
Reported-by: syzbot+26ec90f463db63510f1c@syzkaller.appspotmail.com
First crash: 14d, last: 11d
▶ ▼ Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-15 KASAN: use-after-free Write in config_item_put 22 syz, C 1 9d11h 9d11h 0/2 upstream: reported C repro on 2026/08/02 12:13

Sample crash report:
R13: 00007ffd9762467c R14: 00007ffd97624690 R15: 0000200000000008
---[ end trace 61d64bfae5aea8e5 ]---
==================================================================
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/asm-generic/atomic-instrumented.h:220 [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:151
Write of size 4 at addr ffff88810b3e1424 by task syz-executor257/333

CPU: 1 PID: 333 Comm: syz-executor257 Tainted: G        W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 __dump_stack+0x21/0x24 lib/dump_stack.c:77
 dump_stack_lvl+0x1a7/0x208 lib/dump_stack.c:118
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:435 [inline]
 kasan_report+0x100/0x140 mm/kasan/report.c:452
 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/asm-generic/atomic-instrumented.h:220 [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:151
 configfs_symlink+0x4a6/0x1320 fs/configfs/symlink.c:212
 vfs_symlink+0x339/0x4c0 fs/namei.c:4107
 do_symlinkat+0x10e/0x3d0 fs/namei.c:4134
 __do_sys_symlinkat fs/namei.c:4148 [inline]
 __se_sys_symlinkat fs/namei.c:4145 [inline]
 __x64_sys_symlinkat+0x7b/0x90 fs/namei.c:4145
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7f466f3816b9
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:00007ffd97624668 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 0000200000000200 RCX: 00007f466f3816b9
RDX: 0000200000000300 RSI: 00000000ffffff9c RDI: 0000200000000200
RBP: 0000200000000300 R08: 0000000000000009 R09: 0000000000000009
R10: 0000000000000009 R11: 0000000000000246 R12: 00000000000057c5
R13: 00007ffd9762467c R14: 00007ffd97624690 R15: 0000200000000008

Allocated by task 333:
 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:430 [inline]
 ____kasan_kmalloc mm/kasan/common.c:509 [inline]
 __kasan_kmalloc+0xd4/0x100 mm/kasan/common.c:518
 kasan_kmalloc include/linux/kasan.h:254 [inline]
 kmem_cache_alloc_trace+0x179/0x2e0 mm/slub.c:2979
 kmalloc include/linux/slab.h:555 [inline]
 kzalloc include/linux/slab.h:667 [inline]
 fsg_alloc_inst+0x61/0x5a0 drivers/usb/gadget/function/f_mass_storage.c:3377
 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:636
 configfs_mkdir+0x5d2/0xd90 fs/configfs/dir.c:1354
 vfs_mkdir+0x42c/0x600 fs/namei.c:3798
 do_mkdirat+0x14c/0x340 fs/namei.c:3820
 __do_sys_mkdirat fs/namei.c:3831 [inline]
 __se_sys_mkdirat fs/namei.c:3829 [inline]
 __x64_sys_mkdirat+0x7b/0x90 fs/namei.c:3829
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

Freed by task 334:
 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:362
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:370
 kasan_slab_free include/linux/kasan.h:220 [inline]
 slab_free_hook mm/slub.c:1600 [inline]
 slab_free_freelist_hook+0xc5/0x190 mm/slub.c:1626
 slab_free mm/slub.c:3208 [inline]
 kfree+0xc0/0x270 mm/slub.c:4196
 fsg_free_inst+0x33c/0x420 drivers/usb/gadget/function/f_mass_storage.c:3368
 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:3254
 config_item_cleanup fs/configfs/item.c:130 [inline]
 config_item_release fs/configfs/item.c:139 [inline]
 kref_put include/linux/kref.h:65 [inline]
 config_item_put+0x158/0x210 fs/configfs/item.c:151
 configfs_rmdir+0x89f/0x960 fs/configfs/dir.c:1580
 vfs_rmdir+0x1ab/0x3c0 fs/namei.c:3860
 do_rmdir+0x232/0x630 fs/namei.c:3920
 __do_sys_rmdir fs/namei.c:3938 [inline]
 __se_sys_rmdir fs/namei.c:3936 [inline]
 __x64_sys_rmdir+0x49/0x50 fs/namei.c:3936
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

Last potentially related work creation:
 kasan_save_stack+0x3a/0x60 mm/kasan/common.c:38
 __kasan_record_aux_stack+0xd2/0x100 mm/kasan/generic.c:348
 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:358
 __call_rcu kernel/rcu/tree.c:2980 [inline]
 call_rcu+0x11a/0x1090 kernel/rcu/tree.c:3054
 blkg_release+0x23/0x30 block/blk-cgroup.c:114
 percpu_ref_put_many include/linux/percpu-refcount.h:322 [inline]
 percpu_ref_put include/linux/percpu-refcount.h:338 [inline]
 percpu_ref_call_confirm_rcu lib/percpu-refcount.c:163 [inline]
 percpu_ref_switch_to_atomic_rcu+0x5a3/0x5b0 lib/percpu-refcount.c:200
 rcu_do_batch+0x488/0xaf0 kernel/rcu/tree.c:2494
 rcu_core+0x50a/0xca0 kernel/rcu/tree.c:2735
 rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2748
 __do_softirq+0x255/0x563 kernel/softirq.c:309

The buggy address belongs to the object at ffff88810b3e1400
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 36 bytes inside of
 512-byte region [ffff88810b3e1400, ffff88810b3e1600)
The buggy address belongs to the page:
page:ffffea00042cf800 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10b3e0
head:ffffea00042cf800 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head)
raw: 4000000000010200 ffffea00042abd00 0000000300000003 ffff888100043080
raw: 0000000000000000 0000000000100010 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 2341788940, free_ts 0
 set_page_owner include/linux/page_owner.h:35 [inline]
 post_alloc_hook mm/page_alloc.c:2456 [inline]
 prep_new_page+0x176/0x190 mm/page_alloc.c:2462
 get_page_from_freelist+0x225f/0x23f0 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x29a/0x640 mm/page_alloc.c:5384
 alloc_slab_page mm/slub.c:-1 [inline]
 allocate_slab mm/slub.c:1813 [inline]
 new_slab+0x84/0x3f0 mm/slub.c:1874
 new_slab_objects mm/slub.c:2632 [inline]
 ___slab_alloc+0x2f8/0x4c0 mm/slub.c:2796
 __slab_alloc+0x63/0xa0 mm/slub.c:2836
 slab_alloc_node mm/slub.c:2918 [inline]
 slab_alloc mm/slub.c:2960 [inline]
 kmem_cache_alloc_trace+0x1a8/0x2e0 mm/slub.c:2977
 kmem_cache_alloc_node_trace include/linux/slab.h:443 [inline]
 kmalloc_node include/linux/slab.h:573 [inline]
 kzalloc_node include/linux/slab.h:678 [inline]
 blkg_alloc+0x6d/0x570 block/blk-cgroup.c:158
 blkcg_init_queue+0x2d/0x330 block/blk-cgroup.c:1171
 blk_alloc_queue+0x444/0x5f0 block/blk-core.c:575
 blk_mq_init_queue_data block/blk-mq.c:3171 [inline]
 blk_mq_init_queue+0x37/0xd0 block/blk-mq.c:3190
 scsi_mq_alloc_queue+0x42/0x140 drivers/scsi/scsi_lib.c:1911
 scsi_alloc_sdev+0x611/0x920 drivers/scsi/scsi_scan.c:284
 scsi_probe_and_add_lun+0x17d/0x3370 drivers/scsi/scsi_scan.c:1098
 __scsi_scan_target+0x1d2/0xbf0 drivers/scsi/scsi_scan.c:1581
 scsi_scan_channel drivers/scsi/scsi_scan.c:1669 [inline]
 scsi_scan_host_selected+0x34e/0x600 drivers/scsi/scsi_scan.c:1698
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88810b3e1300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88810b3e1380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88810b3e1400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff88810b3e1480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88810b3e1500: 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: 1 PID: 333 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 1 PID: 333 Comm: syz-executor257 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 e0 48 40 85 e8 7c ca 3a 02 0f 0b eb c3 e8 73 89 26 ff c6 05 b1 75 82 04 01 48 c7 c7 40 49 40 85 e8 60 ca 3a 02 <0f> 0b eb a7 e8 57 89 26 ff c6 05 92 75 82 04 01 48 c7 c7 60 48 40
RSP: 0018:ffffc90000cd7c78 EFLAGS: 00010246
RAX: dd7d2324e10bbd00 RBX: 0000000000000003 RCX: ffff88810b724f00
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc90000cd7c88 R08: ffff8881f7152fbf R09: 1ffff1103ee2a5f7
R10: dffffc0000000000 R11: ffffed103ee2a5f8 R12: 00000000ffffffea
R13: dffffc0000000000 R14: 0000000000000003 R15: 00000000c0000000
FS:  00005555660e73c0(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f466f3a27a2 CR3: 000000010af04000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 __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:151
 configfs_symlink+0x4a6/0x1320 fs/configfs/symlink.c:212
 vfs_symlink+0x339/0x4c0 fs/namei.c:4107
 do_symlinkat+0x10e/0x3d0 fs/namei.c:4134
 __do_sys_symlinkat fs/namei.c:4148 [inline]
 __se_sys_symlinkat fs/namei.c:4145 [inline]
 __x64_sys_symlinkat+0x7b/0x90 fs/namei.c:4145
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7f466f3816b9
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:00007ffd97624668 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 0000200000000200 RCX: 00007f466f3816b9
RDX: 0000200000000300 RSI: 00000000ffffff9c RDI: 0000200000000200
RBP: 0000200000000300 R08: 0000000000000009 R09: 0000000000000009
R10: 0000000000000009 R11: 0000000000000246 R12: 00000000000057c5
R13: 00007ffd9762467c R14: 00007ffd97624690 R15: 0000200000000008
---[ end trace 61d64bfae5aea8e6 ]---

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/31 09:48 android13-5.10-lts 50b3a256e550 aaffb173 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Write in config_item_put
2026/07/28 21:48 android13-5.10-lts 50b3a256e550 edc8a875 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Write in config_item_put
* Struck through repros no longer work on HEAD.