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: 10d, last: 8d14h
▶ ▼ Similar bugs (4)
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 12d 12d 0/3 upstream: reported C repro on 2026/07/25 19:17
android-5-10 KASAN: use-after-free Write in config_item_get 22 syz, C 4 9d21h 11d 0/2 upstream: reported C repro on 2026/07/26 20:05
upstream KASAN: slab-use-after-free Write in config_item_get fs prio:normal 22 syz, C error 8 5d04h 8d18h 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 8d11h 8d12h 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 ffff88811b4ac41c by task syz-executor323/1295

CPU: 0 PID: 1295 Comm: syz-executor323 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
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: 0033:0x7f599dde0d99
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:00007fff7fd55d08 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f599dde0d99
RDX: 0000200000000340 RSI: 00000000ffffff9c RDI: 0000200000000300
RBP: 0000000000000000 R08: 00007fff7fd55d3c R09: 00007fff7fd55d3c
R10: 00007fff7fd55d3c R11: 0000000000000246 R12: 00007fff7fd55d3c
R13: 00007fff7fd55d50 R14: 00007fff7fd55d90 R15: 00000000000000ca
 </TASK>

Allocated by task 1294:
 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]
 afunc_alloc_inst+0x4c/0x560 drivers/usb/gadget/function/f_uac2.c:1917
 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 1294:
 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
 afunc_free_inst+0x15/0x20 drivers/usb/gadget/function/f_uac2.c:1910
 usb_put_function_instance+0x85/0xa0 drivers/usb/gadget/functions.c:77
 f_uac2_attr_release+0x15/0x20 drivers/usb/gadget/function/f_uac2.c:1739
 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

The buggy address belongs to the object at ffff88811b4ac400
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 28 bytes inside of
 512-byte region [ffff88811b4ac400, ffff88811b4ac600)
The buggy address belongs to the page:
page:ffffea00046d2b00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x11b4ac
head:ffffea00046d2b00 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 140, ts 6977440412, 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]
 __kmalloc_track_caller+0x169/0x2c0 mm/slub.c:4954
 kmalloc_reserve net/core/skbuff.c:357 [inline]
 __alloc_skb+0x210/0x730 net/core/skbuff.c:428
 alloc_skb include/linux/skbuff.h:1183 [inline]
 alloc_skb_with_frags+0xa8/0x620 net/core/skbuff.c:6207
 sock_alloc_send_pskb+0x87f/0x9a0 net/core/sock.c:2542
 unix_dgram_sendmsg+0x6f3/0x19b0 net/unix/af_unix.c:1816
 sock_sendmsg_nosec net/socket.c:704 [inline]
 __sock_sendmsg net/socket.c:716 [inline]
 __sys_sendto+0x46d/0x620 net/socket.c:2063
 __do_sys_sendto net/socket.c:2075 [inline]
 __se_sys_sendto net/socket.c:2071 [inline]
 __x64_sys_sendto+0xe5/0x100 net/socket.c:2071
 x64_sys_call+0x178/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:45
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88811b4ac300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88811b4ac380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88811b4ac400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                            ^
 ffff88811b4ac480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88811b4ac500: 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: 1295 at lib/refcount.c:25 refcount_warn_saturate+0x104/0x1a0 lib/refcount.c:25
Modules linked in:
CPU: 0 PID: 1295 Comm: syz-executor323 Tainted: G    B             syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
RIP: 0010:refcount_warn_saturate+0x104/0x1a0 lib/refcount.c:25
Code: 04 01 48 c7 c7 80 47 63 85 e8 c8 47 5a 02 0f 0b eb df e8 5f 80 19 ff c6 05 1b ea 95 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
RSP: 0018:ffffc900022b7c58 EFLAGS: 00010246
RAX: 4e6f7a85674f4700 RBX: 0000000000000002 RCX: ffff88811933cf00
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc900022b7c68 R08: ffffc900022b76c7 R09: 1ffff92000456ed8
R10: dffffc0000000000 R11: fffff52000456ed9 R12: ffff88811dcb9378
R13: dffffc0000000000 R14: 0000000000000002 R15: 0000000000000000
FS:  000055555bb49480(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000000 CR3: 000000010dfff000 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/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: 0033:0x7f599dde0d99
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:00007fff7fd55d08 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f599dde0d99
RDX: 0000200000000340 RSI: 00000000ffffff9c RDI: 0000200000000300
RBP: 0000000000000000 R08: 00007fff7fd55d3c R09: 00007fff7fd55d3c
R10: 00007fff7fd55d3c R11: 0000000000000246 R12: 00007fff7fd55d3c
R13: 00007fff7fd55d50 R14: 00007fff7fd55d90 R15: 00000000000000ca
 </TASK>
---[ end trace 23597a9df383f8ae ]---
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 1295 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Modules linked in:

CPU: 1 PID: 1295 Comm: syz-executor323 Tainted: G    B   W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
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:ffffc900022b7c38 EFLAGS: 00010246

RAX: 4e6f7a85674f4700 RBX: 0000000000000003 RCX: ffff88811933cf00
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc900022b7c48 R08: ffffc900022b76a7 R09: 1ffff92000456ed4
R10: dffffc0000000000 R11: fffff52000456ed5 R12: 00000000ffffffea
R13: dffffc0000000000 R14: 0000000000000003 R15: 00000000c0000000
FS:  000055555bb49480(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f599de3f73c CR3: 000000010dfff000 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+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: 0033:0x7f599dde0d99
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:00007fff7fd55d08 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f599dde0d99
RDX: 0000200000000340 RSI: 00000000ffffff9c RDI: 0000200000000300
RBP: 0000000000000000 R08: 00007fff7fd55d3c R09: 00007fff7fd55d3c
R10: 00007fff7fd55d3c R11: 0000000000000246 R12: 00007fff7fd55d3c
R13: 00007fff7fd55d50 R14: 00007fff7fd55d90 R15: 00000000000000ca
 </TASK>
---[ end trace 23597a9df383f8af ]---

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
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.