KASAN: use-after-free Write in config_item_get

Status: upstream: reported C repro on 2026/07/28 10:17
Reported-by: syzbot+680594a918d6fb148377@syzkaller.appspotmail.com
First crash: 48d, last: 20d
▶ ▼ Similar bugs (6)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 KASAN: use-after-free Write in config_item_get origin:upstream 22 syz, C error 1 51d 51d 0/3 upstream: reported C repro on 2026/07/25 19:17
android-6-1 KASAN: use-after-free Write in config_item_get origin:upstream 22 syz, C 3 1d23h 25d 0/2 upstream: reported C repro on 2026/08/20 12:37
android-5-10 KASAN: use-after-free Write in config_item_get 22 syz, C 4 22d 50d 0/2 upstream: reported C repro on 2026/07/26 20:05
linux-6.6 KASAN: slab-use-after-free Write in config_item_get origin:lts-only 22 syz, C 1 5d18h 37d 0/2 upstream: reported C repro on 2026/08/09 00:32
upstream KASAN: slab-use-after-free Write in config_item_get prio:normal fs 22 syz, C error 8 27d 47d 1/29 upstream: reported C repro on 2026/07/30 00:19
android-6-12 KASAN: slab-use-after-free Write in config_item_get origin:upstream 22 syz 2 29d 46d 0/1 premoderation: reported syz repro on 2026/07/30 06:38

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
BUG: KASAN: use-after-free in atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:111 [inline]
BUG: KASAN: use-after-free in __refcount_add include/linux/refcount.h:193 [inline]
BUG: KASAN: use-after-free in __refcount_inc include/linux/refcount.h:250 [inline]
BUG: KASAN: use-after-free in refcount_inc include/linux/refcount.h:267 [inline]
BUG: KASAN: use-after-free in kref_get include/linux/kref.h:45 [inline]
BUG: KASAN: use-after-free in config_item_get+0x27/0x90 fs/configfs/item.c:104
Write of size 4 at addr ffff88810cb9ae1c by task syz.0.137/645

CPU: 1 PID: 645 Comm: syz.0.137 Not tainted 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_add_relaxed include/linux/atomic/atomic-instrumented.h:111 [inline]
 __refcount_add include/linux/refcount.h:193 [inline]
 __refcount_inc include/linux/refcount.h:250 [inline]
 refcount_inc include/linux/refcount.h:267 [inline]
 kref_get include/linux/kref.h:45 [inline]
 config_item_get+0x27/0x90 fs/configfs/item.c:104
 configfs_get_config_item fs/configfs/configfs_internal.h:128 [inline]
 get_target fs/configfs/symlink.c:125 [inline]
 configfs_symlink+0x44f/0x1330 fs/configfs/symlink.c:191
 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: 0033:0x7ff296dd30d9
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:00007ff296c34028 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 00007ff29705afa0 RCX: 00007ff296dd30d9
RDX: 00002000000002c0 RSI: ffffffffffffff9c RDI: 0000200000000280
RBP: 00007ff296e6a024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff29705b038 R14: 00007ff29705afa0 R15: 00007fff87f60018
 </TASK>

Allocated by task 637:
 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]
 geth_alloc_inst+0x4e/0x120 drivers/usb/gadget/function/f_subset.c:434
 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 639:
 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
 geth_free_inst+0x8c/0xb0 drivers/usb/gadget/function/f_subset.c:427
 usb_put_function_instance+0x85/0xa0 drivers/usb/gadget/functions.c:77
 gether_attr_release+0x15/0x20 drivers/usb/gadget/function/f_subset.c:390
 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_unlinkat fs/namei.c:4398 [inline]
 __se_sys_unlinkat fs/namei.c:4392 [inline]
 __x64_sys_unlinkat+0xc7/0xf0 fs/namei.c:4392
 x64_sys_call+0x4c0/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:264
 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

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
 kvfree_call_rcu+0xb6/0x860 kernel/rcu/tree.c:3648
 ep_free fs/eventpoll.c:709 [inline]
 ep_clear_and_put+0x38c/0x3e0 fs/eventpoll.c:824
 ep_eventpoll_release+0x48/0x60 fs/eventpoll.c:832
 __fput+0x22b/0x900 fs/file_table.c:311
 ____fput+0x15/0x20 fs/file_table.c:339
 task_work_run+0x127/0x190 kernel/task_work.c:188
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop+0xd0/0xe0 kernel/entry/common.c:181
 exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:214
 __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
 syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:307
 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 ffff88810cb9ae00
 which belongs to the cache kmalloc-256 of size 256
The buggy address is located 28 bytes inside of
 256-byte region [ffff88810cb9ae00, ffff88810cb9af00)
The buggy address belongs to the page:
page:ffffea000432e680 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10cb9a
head:ffffea000432e680 order:1 compound_mapcount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea00043c0700 0000000900000009 ffff888100042d80
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 1, migratetype Unmovable, gfp_mask 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 102, ts 5596314195, free_ts 0
 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]
 inode_doinit_use_xattr+0x5d/0x3f0 security/selinux/hooks.c:1395
 inode_doinit_with_dentry+0x945/0xd90 security/selinux/hooks.c:1586
 selinux_d_instantiate+0x27/0x40 security/selinux/hooks.c:6496
 security_d_instantiate+0x9e/0xf0 security/security.c:2075
 d_splice_alias+0x6d/0x390 fs/dcache.c:3073
 kernfs_iop_lookup+0x2c2/0x310 fs/kernfs/dir.c:1175
 __lookup_slow+0x2b8/0x410 fs/namei.c:1671
 lookup_slow+0x57/0x70 fs/namei.c:1688
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88810cb9ad00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88810cb9ad80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88810cb9ae00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                            ^
 ffff88810cb9ae80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88810cb9af00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================
------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 1 PID: 645 at lib/refcount.c:25 refcount_warn_saturate+0x104/0x1a0 lib/refcount.c:25
Modules linked in:
CPU: 1 PID: 645 Comm: syz.0.137 Tainted: G    B             syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:refcount_warn_saturate+0x104/0x1a0 lib/refcount.c:25
Code: 04 01 48 c7 c7 c0 4c 63 85 e8 58 85 5a 02 0f 0b eb df e8 bf 7e 19 ff c6 05 ab f2 95 04 01 48 c7 c7 00 4c 63 85 e8 3c 85 5a 02 <0f> 0b eb c3 e8 a3 7e 19 ff c6 05 90 f2 95 04 01 48 c7 c7 60 4c 63
RSP: 0018:ffffc900016d7c58 EFLAGS: 00010246
RAX: 062c55e221e69b00 RBX: 0000000000000002 RCX: ffff88811d22e2c0
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc900016d7c68 R08: ffffc900016d76c7 R09: 1ffff920002daed8
R10: dffffc0000000000 R11: fffff520002daed9 R12: ffff88811cd30f30
R13: dffffc0000000000 R14: 0000000000000002 R15: 0000000000000000
FS:  00007ff296c346c0(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b34063fff CR3: 000000011b60b000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 __refcount_add include/linux/refcount.h:-1 [inline]
 __refcount_inc include/linux/refcount.h:250 [inline]
 refcount_inc include/linux/refcount.h:267 [inline]
 kref_get include/linux/kref.h:45 [inline]
 config_item_get+0x8c/0x90 fs/configfs/item.c:104
 configfs_get_config_item fs/configfs/configfs_internal.h:128 [inline]
 get_target fs/configfs/symlink.c:125 [inline]
 configfs_symlink+0x44f/0x1330 fs/configfs/symlink.c:191
 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: 0033:0x7ff296dd30d9
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:00007ff296c34028 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 00007ff29705afa0 RCX: 00007ff296dd30d9
RDX: 00002000000002c0 RSI: ffffffffffffff9c RDI: 0000200000000280
RBP: 00007ff296e6a024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff29705b038 R14: 00007ff29705afa0 R15: 00007fff87f60018
 </TASK>
---[ end trace 0c8782d58ef450e3 ]---
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 645 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 0 PID: 645 Comm: syz.0.137 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 00 4c 63 85 e8 3c 85 5a 02 0f 0b eb c3 e8 a3 7e 19 ff c6 05 90 f2 95 04 01 48 c7 c7 60 4c 63 85 e8 20 85 5a 02 <0f> 0b eb a7 e8 87 7e 19 ff c6 05 71 f2 95 04 01 48 c7 c7 a0 4b 63
RSP: 0018:ffffc900016d7c38 EFLAGS: 00010246
RAX: 062c55e221e69b00 RBX: 0000000000000003 RCX: ffff88811d22e2c0
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc900016d7c48 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520002daee8 R12: 00000000ffffffea
R13: dffffc0000000000 R14: 0000000000000003 R15: 00000000c0000000
FS:  00007ff296c346c0(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f6a081d67c0 CR3: 000000011b60b000 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: 0033:0x7ff296dd30d9
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:00007ff296c34028 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 00007ff29705afa0 RCX: 00007ff296dd30d9
RDX: 00002000000002c0 RSI: ffffffffffffff9c RDI: 0000200000000280
RBP: 00007ff296e6a024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff29705b038 R14: 00007ff29705afa0 R15: 00007fff87f60018
 </TASK>
---[ end trace 0c8782d58ef450e5 ]---

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/25 11:22 android13-5.15-lts 0ebdd0175e37 614e416a .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Write in config_item_get
2026/07/30 04:53 android13-5.15-lts 61d896ee2a80 6ef5c1e2 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Write in config_item_get
2026/07/30 04:19 android13-5.15-lts 61d896ee2a80 6ef5c1e2 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Write in config_item_get
2026/07/29 04:35 android13-5.15-lts 61d896ee2a80 19622d9d .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Write in config_item_get
2026/07/28 10:17 android13-5.15-lts 61d896ee2a80 45ae1df4 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Write in config_item_get
2026/07/28 11:19 android13-5.15-lts 61d896ee2a80 45ae1df4 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Write in config_item_get
* Struck through repros no longer work on HEAD.