KASAN: use-after-free Write in config_item_get

Status: upstream: reported C repro on 2026/08/20 12:37
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+10bc877cff561a7d7300@syzkaller.appspotmail.com
First crash: 4d13h, last: 3d12h
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2026/08/22 lts (merge base) 228da13e907e C [report] KASAN: use-after-free Write in config_item_put
2026/08/22 upstream (ToT) 26260251022f C [report] KASAN: slab-use-after-free Read in configfs_dirent_is_ready
▶ ▼ 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 1 30d 30d 0/3 upstream: reported C repro on 2026/07/25 19:17
android-5-15 KASAN: use-after-free Write in config_item_get 22 syz, C 5 25d 27d 0/2 upstream: reported C repro on 2026/07/28 10:17
android-5-10 KASAN: use-after-free Write in config_item_get 22 syz, C 4 1d00h 29d 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 22 syz, C 1 16d 16d 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 6d10h 26d 0/29 upstream: reported C repro on 2026/07/30 00:19
android-6-12 KASAN: slab-use-after-free Write in config_item_get 22 syz 2 8d03h 25d 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:102 [inline]
BUG: KASAN: use-after-free in atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:116 [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 ffff8881127b981c by task syz-executor326/3933

CPU: 0 PID: 3933 Comm: syz-executor326 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 __dump_stack+0x21/0x24 lib/dump_stack.c:88
 dump_stack_lvl+0x110/0x170 lib/dump_stack.c:106
 print_address_description+0x71/0x200 mm/kasan/report.c:316
 print_report+0x4a/0x60 mm/kasan/report.c:420
 kasan_report+0x122/0x150 mm/kasan/report.c:524
 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:102 [inline]
 atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:116 [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/0x1360 fs/configfs/symlink.c:191
 vfs_symlink+0x261/0x3f0 fs/namei.c:4478
 do_symlinkat+0x24a/0x5d0 fs/namei.c:4507
 __do_sys_symlinkat fs/namei.c:4524 [inline]
 __se_sys_symlinkat fs/namei.c:4521 [inline]
 __x64_sys_symlinkat+0x99/0xb0 fs/namei.c:4521
 x64_sys_call+0x282/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:267
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fa17d612169
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:00007ffec12d5df8 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 000000000000b582 RCX: 00007fa17d612169
RDX: 0000200000000340 RSI: 00000000ffffff9c RDI: 0000200000000300
RBP: 0000000000000000 R08: 00007ffec12d5e2c R09: 00007ffec12d5e2c
R10: 00007ffec12d5e2c R11: 0000000000000246 R12: 00007ffec12d5e2c
R13: 00007ffec12d5e60 R14: 00007ffec12d5e40 R15: 00000000000002b1
 </TASK>

Allocated by task 3932:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 kasan_save_alloc_info+0x1f/0x30 mm/kasan/generic.c:505
 ____kasan_kmalloc mm/kasan/common.c:380 [inline]
 __kasan_kmalloc+0x95/0xb0 mm/kasan/common.c:389
 kasan_kmalloc include/linux/kasan.h:212 [inline]
 kmalloc_trace+0x40/0xb0 mm/slab_common.c:1033
 kmalloc include/linux/slab.h:563 [inline]
 kzalloc include/linux/slab.h:699 [inline]
 afunc_alloc_inst+0x4a/0x5e0 drivers/usb/gadget/function/f_uac2.c:2150
 try_get_usb_function_instance drivers/usb/gadget/functions.c:28 [inline]
 usb_get_function_instance+0xf3/0x310 drivers/usb/gadget/functions.c:44
 function_make+0x118/0x360 drivers/usb/gadget/configfs.c:652
 configfs_mkdir+0x518/0x9e0 fs/configfs/dir.c:1329
 vfs_mkdir+0x39c/0x580 fs/namei.c:4113
 do_mkdirat+0x174/0x4d0 fs/namei.c:4138
 __do_sys_mkdirat fs/namei.c:4153 [inline]
 __se_sys_mkdirat fs/namei.c:4151 [inline]
 __x64_sys_mkdirat+0x89/0xa0 fs/namei.c:4151
 x64_sys_call+0x73d/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:259
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Freed by task 3932:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:516
 ____kasan_slab_free+0x132/0x180 mm/kasan/common.c:242
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:250
 kasan_slab_free include/linux/kasan.h:178 [inline]
 slab_free_hook mm/slub.c:1750 [inline]
 slab_free_freelist_hook+0xc2/0x190 mm/slub.c:1776
 slab_free mm/slub.c:3712 [inline]
 __kmem_cache_free+0xb7/0x1b0 mm/slub.c:3728
 kfree+0x6f/0xf0 mm/slab_common.c:990
 afunc_free_inst+0x15/0x20 drivers/usb/gadget/function/f_uac2.c:2143
 usb_put_function_instance+0x9b/0xc0 drivers/usb/gadget/functions.c:77
 f_uac2_attr_release+0x15/0x20 drivers/usb/gadget/function/f_uac2.c:1865
 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+0x166/0x210 fs/configfs/item.c:149
 configfs_rmdir+0x8c9/0x980 fs/configfs/dir.c:1540
 vfs_rmdir+0x381/0x4f0 fs/namei.c:4198
 do_rmdir+0x261/0x6b0 fs/namei.c:4259
 __do_sys_unlinkat fs/namei.c:4439 [inline]
 __se_sys_unlinkat fs/namei.c:4433 [inline]
 __x64_sys_unlinkat+0xc7/0xf0 fs/namei.c:4433
 x64_sys_call+0x79f/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:264
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff8881127b9800
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 28 bytes inside of
 512-byte region [ffff8881127b9800, ffff8881127b9a00)

The buggy address belongs to the physical page:
page:ffffea000449ee00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1127b8
head:ffffea000449ee00 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 dead000000000100 dead000000000122 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 111, tgid 111 (udevadm), ts 4988166257, free_ts 0
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f5/0x210 mm/page_alloc.c:2672
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2679
 get_page_from_freelist+0x2ca9/0x2d20 mm/page_alloc.c:4586
 __alloc_pages+0x1fa/0x610 mm/page_alloc.c:5930
 alloc_slab_page+0x6e/0xf0 include/linux/gfp.h:-1
 allocate_slab mm/slub.c:1967 [inline]
 new_slab+0x98/0x3e0 mm/slub.c:2020
 ___slab_alloc+0x70f/0xb70 mm/slub.c:3177
 __slab_alloc+0x5e/0xa0 mm/slub.c:3263
 slab_alloc_node mm/slub.c:3348 [inline]
 __kmem_cache_alloc_node+0x204/0x2d0 mm/slub.c:3423
 __do_kmalloc_node mm/slab_common.c:937 [inline]
 __kmalloc_node_track_caller+0xa1/0x1e0 mm/slab_common.c:958
 kmalloc_reserve net/core/skbuff.c:449 [inline]
 __alloc_skb+0x226/0x4a0 net/core/skbuff.c:518
 alloc_skb include/linux/skbuff.h:1322 [inline]
 alloc_uevent_skb+0x85/0x240 lib/kobject_uevent.c:290
 uevent_net_broadcast_untagged lib/kobject_uevent.c:326 [inline]
 kobject_uevent_net_broadcast+0x343/0x5b0 lib/kobject_uevent.c:409
 kobject_uevent_env+0x541/0x720 lib/kobject_uevent.c:608
 kobject_synth_uevent+0x457/0x940 lib/kobject_uevent.c:208
 uevent_store+0x25/0x70 drivers/base/core.c:2690
page_owner free stack trace missing

Memory state around the buggy address:
 ffff8881127b9700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8881127b9780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8881127b9800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                            ^
 ffff8881127b9880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881127b9900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 0 PID: 3933 at lib/refcount.c:25 refcount_warn_saturate+0x104/0x1a0 lib/refcount.c:25
Modules linked in:
CPU: 0 PID: 3933 Comm: syz-executor326 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: 05 01 48 c7 c7 40 0d ca 85 e8 d8 28 d9 fe 0f 0b eb df e8 2f 9a 08 ff c6 05 0f ca 26 05 01 48 c7 c7 80 0c ca 85 e8 bc 28 d9 fe <0f> 0b eb c3 e8 13 9a 08 ff c6 05 f4 c9 26 05 01 48 c7 c7 e0 0c ca
RSP: 0018:ffffc900070e7c58 EFLAGS: 00010246
RAX: fc5511f1e0d85d00 RBX: 0000000000000002 RCX: ffff88811a33d100
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
RBP: ffffc900070e7c68 R08: ffffc900070e7847 R09: 1ffff92000e1cf08
R10: dffffc0000000000 R11: fffff52000e1cf09 R12: ffff8881138004e0
R13: dffffc0000000000 R14: 0000000000000002 R15: 0000000000000000
FS:  000055556c898480(0000) GS:ffff8881f6e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000000 CR3: 00000001137cd000 CR4: 00000000003506b0
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/0x1360 fs/configfs/symlink.c:191
 vfs_symlink+0x261/0x3f0 fs/namei.c:4478
 do_symlinkat+0x24a/0x5d0 fs/namei.c:4507
 __do_sys_symlinkat fs/namei.c:4524 [inline]
 __se_sys_symlinkat fs/namei.c:4521 [inline]
 __x64_sys_symlinkat+0x99/0xb0 fs/namei.c:4521
 x64_sys_call+0x282/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:267
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fa17d612169
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:00007ffec12d5df8 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 000000000000b582 RCX: 00007fa17d612169
RDX: 0000200000000340 RSI: 00000000ffffff9c RDI: 0000200000000300
RBP: 0000000000000000 R08: 00007ffec12d5e2c R09: 00007ffec12d5e2c
R10: 00007ffec12d5e2c R11: 0000000000000246 R12: 00007ffec12d5e2c
R13: 00007ffec12d5e60 R14: 00007ffec12d5e40 R15: 00000000000002b1
 </TASK>
---[ end trace 0000000000000000 ]---
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 3933 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 1 PID: 3933 Comm: syz-executor326 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: 05 01 48 c7 c7 80 0c ca 85 e8 bc 28 d9 fe 0f 0b eb c3 e8 13 9a 08 ff c6 05 f4 c9 26 05 01 48 c7 c7 e0 0c ca 85 e8 a0 28 d9 fe <0f> 0b eb a7 e8 f7 99 08 ff c6 05 d5 c9 26 05 01 48 c7 c7 20 0c ca
RSP: 0018:ffffc900070e7c38 EFLAGS: 00010246
RAX: fc5511f1e0d85d00 RBX: 0000000000000003 RCX: ffff88811a33d100
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002
RBP: ffffc900070e7c48 R08: ffffc900070e7947 R09: 1ffff92000e1cf28
R10: dffffc0000000000 R11: fffff52000e1cf29 R12: 00000000ffffffef
R13: dffffc0000000000 R14: 0000000000000003 R15: 00000000c0000000
FS:  000055556c898480(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa17d6ab3c0 CR3: 00000001137cd000 CR4: 00000000003506a0
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+0x20e/0x210 fs/configfs/item.c:149
 configfs_symlink+0x4a6/0x1360 fs/configfs/symlink.c:212
 vfs_symlink+0x261/0x3f0 fs/namei.c:4478
 do_symlinkat+0x24a/0x5d0 fs/namei.c:4507
 __do_sys_symlinkat fs/namei.c:4524 [inline]
 __se_sys_symlinkat fs/namei.c:4521 [inline]
 __x64_sys_symlinkat+0x99/0xb0 fs/namei.c:4521
 x64_sys_call+0x282/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:267
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fa17d612169
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:00007ffec12d5df8 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 000000000000b582 RCX: 00007fa17d612169
RDX: 0000200000000340 RSI: 00000000ffffff9c RDI: 0000200000000300
RBP: 0000000000000000 R08: 00007ffec12d5e2c R09: 00007ffec12d5e2c
R10: 00007ffec12d5e2c R11: 0000000000000246 R12: 00007ffec12d5e2c
R13: 00007ffec12d5e60 R14: 00007ffec12d5e40 R15: 00000000000002b1
 </TASK>
---[ end trace 0000000000000000 ]---

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/21 13:19 android14-6.1 92668decd5e0 1e72964b .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Write in config_item_get
2026/08/20 12:35 android14-6.1 92668decd5e0 1e72964b .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Write in config_item_get
2026/08/21 13:52 android14-6.1 92668decd5e0 1e72964b .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Write in config_item_get
* Struck through repros no longer work on HEAD.