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: 34d, last: 9d00h
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-6-1 KASAN: use-after-free Write in config_item_put 22 syz, C 2 11d 11d 0/2 upstream: reported C repro on 2026/08/20 01:54
android-5-15 KASAN: use-after-free Write in config_item_put 22 syz, C 1 29d 29d 0/2 upstream: reported C repro on 2026/08/02 12:13

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_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 ffff888117c4c61c by task syz-executor823/1011

CPU: 0 PID: 1011 Comm: syz-executor823 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: 0033:0x7f92c29aa749
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:00007ffe4cfa4aa8 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f92c29aa749
RDX: 00002000000002c0 RSI: 00000000ffffff9c RDI: 0000200000000280
RBP: 0000000000000000 R08: 0000000000000003 R09: 0000000000000003
R10: 0000000000000003 R11: 0000000000000246 R12: 00007ffe4cfa4adc
R13: 00007ffe4cfa4af0 R14: 00007ffe4cfa4b30 R15: 000000000000008a

Allocated by task 1010:
 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]
 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:636
 configfs_mkdir+0x5d2/0xd90 fs/configfs/dir.c:1382
 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 1010:
 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
 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: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:1608
 vfs_rmdir+0x1ab/0x3c0 fs/namei.c:3860
 do_rmdir+0x232/0x630 fs/namei.c:3920
 __do_sys_unlinkat fs/namei.c:4084 [inline]
 __se_sys_unlinkat fs/namei.c:4078 [inline]
 __x64_sys_unlinkat+0xc7/0xf0 fs/namei.c:4078
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

The buggy address belongs to the object at ffff888117c4c600
 which belongs to the cache kmalloc-256 of size 256
The buggy address is located 28 bytes inside of
 256-byte region [ffff888117c4c600, ffff888117c4c700)
The buggy address belongs to the page:
page:ffffea00045f1300 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x117c4c
head:ffffea00045f1300 order:1 compound_mapcount:0
flags: 0x4000000000010200(slab|head)
raw: 4000000000010200 ffffea000485de00 0000000d0000000d ffff888100043200
raw: 0000000000000000 0000000080100010 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 0x1d60c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 371, ts 30209698284, free_ts 30150339497
 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]
 __kmalloc+0x1f9/0x330 mm/slub.c:4034
 __kmalloc_node include/linux/slab.h:421 [inline]
 kmalloc_node include/linux/slab.h:578 [inline]
 kvmalloc_node+0x88/0x130 mm/util.c:612
 kvmalloc include/linux/mm.h:833 [inline]
 kvzalloc include/linux/mm.h:841 [inline]
 netif_alloc_rx_queues net/core/dev.c:9855 [inline]
 alloc_netdev_mqs+0x857/0xca0 net/core/dev.c:10593
 alloc_etherdev_mqs+0x34/0x40 net/ethernet/eth.c:388
 gether_setup_name_default+0x29/0x550 drivers/usb/gadget/function/u_ether.c:829
 gether_setup_default drivers/usb/gadget/function/u_ether.h:140 [inline]
 geth_alloc_inst+0xa8/0x120 drivers/usb/gadget/function/f_subset.c:439
 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:1382
 vfs_mkdir+0x42c/0x600 fs/namei.c:3798
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:28 [inline]
 free_pages_prepare mm/page_alloc.c:1349 [inline]
 __free_pages_ok+0x80b/0x830 mm/page_alloc.c:1629
 free_the_page mm/page_alloc.c:5445 [inline]
 __free_pages+0xd8/0x390 mm/page_alloc.c:5454
 __free_slab+0xcf/0x190 mm/slub.c:1899
 free_slab mm/slub.c:1914 [inline]
 discard_slab mm/slub.c:1920 [inline]
 unfreeze_partials+0x150/0x180 mm/slub.c:2415
 put_cpu_partial+0xc1/0x180 mm/slub.c:2451
 __slab_free+0x2c9/0x3a0 mm/slub.c:3100
 do_slab_free mm/slub.c:3196 [inline]
 ___cache_free+0x10e/0x130 mm/slub.c:3215
 qlink_free+0x50/0x90 mm/kasan/quarantine.c:157
 qlist_free_all+0x5f/0xb0 mm/kasan/quarantine.c:176
 kasan_quarantine_reduce+0x14a/0x160 mm/kasan/quarantine.c:283
 __kasan_slab_alloc+0x2f/0xe0 mm/kasan/common.c:440
 kasan_slab_alloc include/linux/kasan.h:244 [inline]
 slab_post_alloc_hook+0x5d/0x2f0 mm/slab.h:580
 slab_alloc_node mm/slub.c:2952 [inline]
 slab_alloc mm/slub.c:2960 [inline]
 kmem_cache_alloc+0x15a/0x2d0 mm/slub.c:2965
 getname_flags+0xba/0x510 fs/namei.c:141
 user_path_at_empty+0x2f/0x50 fs/namei.c:2748
 user_path_at include/linux/namei.h:60 [inline]
 vfs_statx+0x10a/0x530 fs/stat.c:193

Memory state around the buggy address:
 ffff888117c4c500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888117c4c580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888117c4c600: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                            ^
 ffff888117c4c680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888117c4c700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 1011 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 0 PID: 1011 Comm: syz-executor823 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 40 4d 40 85 e8 ec 0e 3b 02 0f 0b eb c3 e8 63 a8 26 ff c6 05 81 8b 82 04 01 48 c7 c7 a0 4d 40 85 e8 d0 0e 3b 02 <0f> 0b eb a7 e8 47 a8 26 ff c6 05 62 8b 82 04 01 48 c7 c7 c0 4c 40
RSP: 0018:ffffc90001987c78 EFLAGS: 00010246
RAX: f6d5e2cce4841200 RBX: 0000000000000003 RCX: ffff888118fc0000
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc90001987c88 R08: 0000000000000003 R09: fffff52000330ef4
R10: dffffc0000000000 R11: fffff52000330ed4 R12: 00000000ffffffea
R13: dffffc0000000000 R14: 0000000000000003 R15: 00000000c0000000
FS:  000055557d328480(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f92c2a3a100 CR3: 000000010fc57000 CR4: 00000000003506b0
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: 0033:0x7f92c29aa749
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:00007ffe4cfa4aa8 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f92c29aa749
RDX: 00002000000002c0 RSI: 00000000ffffff9c RDI: 0000200000000280
RBP: 0000000000000000 R08: 0000000000000003 R09: 0000000000000003
R10: 0000000000000003 R11: 0000000000000246 R12: 00007ffe4cfa4adc
R13: 00007ffe4cfa4af0 R14: 00007ffe4cfa4b30 R15: 000000000000008a
---[ end trace 08c3f2d6af8ebad0 ]---

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/18 08:18 android13-5.10-lts e334a66065d3 1e72964b .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
2026/07/31 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
2026/08/22 22:23 android13-5.10-lts e334a66065d3 1e72964b .config console log report info [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.