KASAN: use-after-free Read in kernfs_find_ns

Status: upstream: reported C repro on 2026/08/01 21:32
Reported-by: syzbot+dc2b9b6017fc273fee9a@syzkaller.appspotmail.com
First crash: 32d, last: 12h24m
▶ ▼ Bug presence (1)
Date Name Commit Repro Result
2026/08/24 upstream (ToT) [unknown] C Failed due to an error; will retry later
▶ ▼ Similar bugs (6)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream general protection fault in kernfs_find_ns kernfs 2 2 1739d 1733d 0/29 auto-closed as invalid on 2022/03/29 00:22
linux-5.15 KASAN: slab-out-of-bounds Read in kernfs_find_ns 17 2 318d 325d 0/3 auto-obsoleted due to no activity on 2026/01/28 00:39
android-54 general protection fault in kernfs_find_ns 2 1 1930d 1930d 0/2 auto-closed as invalid on 2021/09/18 09:16
android-5-10 general protection fault in kernfs_find_ns 2 syz, C error 13 134d 1089d 0/2 upstream: reported C repro on 2023/09/09 18:30
linux-5.15 KASAN: global-out-of-bounds Read in kernfs_find_ns 17 1 460d 460d 0/3 auto-obsoleted due to no activity on 2025/09/08 00:48
android-54 general protection fault in kernfs_find_ns (2) 2 syz, C 21 519d 1774d 0/2 upstream: reported C repro on 2021/10/24 20:02
▶ ▼ Fix bisection attempts (1)
Created Duration User Patch Repo Result
2026/09/02 16:49 2h26m bisect fix linux-6.1.y OK (0) job log log

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in strlen+0x53/0x60 lib/string.c:502
Read of size 1 at addr ffff88805a5566a0 by task syz.1.566/5060

CPU: 1 PID: 5060 Comm: syz.1.566 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x24e lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:316 [inline]
 print_report+0xa8/0x210 mm/kasan/report.c:420
 kasan_report+0x10b/0x140 mm/kasan/report.c:524
 strlen+0x53/0x60 lib/string.c:502
 __fortify_strlen include/linux/fortify-string.h:196 [inline]
 kernfs_name_hash fs/kernfs/dir.c:318 [inline]
 kernfs_find_ns+0x12b/0x550 fs/kernfs/dir.c:840
 kernfs_remove_by_name_ns+0x86/0x150 fs/kernfs/dir.c:1664
 driver_sysfs_remove drivers/base/dd.c:475 [inline]
 __device_release_driver drivers/base/dd.c:1270 [inline]
 device_release_driver_internal+0x36c/0x7c0 drivers/base/dd.c:1305
 bus_remove_device+0x2dd/0x400 drivers/base/bus.c:531
 device_del+0x63f/0xa80 drivers/base/core.c:3900
 usb_del_gadget+0x18c/0x250 drivers/usb/gadget/udc/core.c:1580
 usb_del_gadget_udc+0x11/0x30 drivers/usb/gadget/udc/core.c:1603
 dummy_udc_remove+0x54/0x60 drivers/usb/gadget/udc/dummy_hcd.c:1123
 platform_remove+0x92/0xe0 drivers/base/platform.c:1422
 device_remove drivers/base/dd.c:547 [inline]
 __device_release_driver drivers/base/dd.c:1279 [inline]
 device_release_driver_internal+0x47d/0x7c0 drivers/base/dd.c:1305
 unbind_store+0x2e2/0x300 drivers/base/bus.c:193
 kernfs_fop_write_iter+0x3a0/0x520 fs/kernfs/file.c:352
 call_write_iter include/linux/fs.h:2265 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x482/0x9a0 fs/read_write.c:584
 ksys_write+0x14d/0x260 fs/read_write.c:637
 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: 0033:0x7fc45d59e019
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:00007ffcada7aa38 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fc45d825fa0 RCX: 00007fc45d59e019
RDX: 000000000000000b RSI: 0000200000000400 RDI: 0000000000000004
RBP: 00007fc45d63500c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc45d825fac R14: 00007fc45d825fa0 R15: 00007fc45d825fa0
 </TASK>

Allocated by task 5059:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 ____kasan_kmalloc mm/kasan/common.c:375 [inline]
 __kasan_kmalloc+0x8e/0xa0 mm/kasan/common.c:384
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 __do_kmalloc_node mm/slab_common.c:936 [inline]
 __kmalloc_node_track_caller+0xb0/0x240 mm/slab_common.c:956
 kvasprintf+0xe8/0x1a0 lib/kasprintf.c:25
 kobject_set_name_vargs+0x5d/0x110 lib/kobject.c:265
 dev_set_name+0xdf/0x130 drivers/base/core.c:3485
 usb_add_gadget+0x474/0x6f0 drivers/usb/gadget/udc/core.c:1448
 usb_add_gadget_udc_release+0x198/0x1e0 drivers/usb/gadget/udc/core.c:1506
 dummy_udc_probe+0x686/0x780 drivers/usb/gadget/udc/dummy_hcd.c:1102
 platform_probe+0x137/0x1c0 drivers/base/platform.c:1400
 call_driver_probe drivers/base/dd.c:-1 [inline]
 really_probe+0x24a/0xb40 drivers/base/dd.c:638
 __driver_probe_device+0x1f5/0x390 drivers/base/dd.c:804
 device_driver_attach+0xd9/0x1c0 drivers/base/dd.c:1131
 bind_store+0x33b/0x380 drivers/base/bus.c:216
 kernfs_fop_write_iter+0x3a0/0x520 fs/kernfs/file.c:352
 call_write_iter include/linux/fs.h:2265 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x482/0x9a0 fs/read_write.c:584
 ksys_write+0x14d/0x260 fs/read_write.c:637
 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 5060:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 kasan_save_free_info+0x27/0x40 mm/kasan/generic.c:516
 ____kasan_slab_free+0x126/0x1f0 mm/kasan/common.c:237
 kasan_slab_free include/linux/kasan.h:177 [inline]
 slab_free_hook mm/slub.c:1729 [inline]
 slab_free_freelist_hook+0x133/0x1b0 mm/slub.c:1755
 slab_free mm/slub.c:3687 [inline]
 __kmem_cache_free+0xb6/0x200 mm/slub.c:3700
 kobject_cleanup lib/kobject.c:687 [inline]
 kobject_release lib/kobject.c:712 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x25c/0x450 lib/kobject.c:729
 bus_remove_device+0x2bf/0x400 drivers/base/bus.c:527
 device_del+0x63f/0xa80 drivers/base/core.c:3900
 usb_del_gadget+0x18c/0x250 drivers/usb/gadget/udc/core.c:1580
 usb_del_gadget_udc+0x11/0x30 drivers/usb/gadget/udc/core.c:1603
 dummy_udc_remove+0x54/0x60 drivers/usb/gadget/udc/dummy_hcd.c:1123
 platform_remove+0x92/0xe0 drivers/base/platform.c:1422
 device_remove drivers/base/dd.c:547 [inline]
 __device_release_driver drivers/base/dd.c:1279 [inline]
 device_release_driver_internal+0x47d/0x7c0 drivers/base/dd.c:1305
 unbind_store+0x2e2/0x300 drivers/base/bus.c:193
 kernfs_fop_write_iter+0x3a0/0x520 fs/kernfs/file.c:352
 call_write_iter include/linux/fs.h:2265 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x482/0x9a0 fs/read_write.c:584
 ksys_write+0x14d/0x260 fs/read_write.c:637
 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 ffff88805a5566a0
 which belongs to the cache kmalloc-16 of size 16
The buggy address is located 0 bytes inside of
 16-byte region [ffff88805a5566a0, ffff88805a5566b0)

The buggy address belongs to the physical page:
page:ffffea0001695580 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88805a556600 pfn:0x5a556
flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000200 0000000000000000 dead000000000001 ffff8880174413c0
raw: ffff88805a556600 0000000080800075 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x112cc0(GFP_USER|__GFP_NOWARN|__GFP_NORETRY), pid 4306, tgid 4306 (syz-executor), ts 84771601701, free_ts 23816808739
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x173/0x1a0 mm/page_alloc.c:2560
 prep_new_page mm/page_alloc.c:2567 [inline]
 get_page_from_freelist+0x206b/0x2180 mm/page_alloc.c:4358
 __alloc_pages+0x1ec/0x4f0 mm/page_alloc.c:5658
 __alloc_pages_node include/linux/gfp.h:237 [inline]
 alloc_slab_page+0x4f/0x180 mm/slub.c:1801
 allocate_slab mm/slub.c:1944 [inline]
 new_slab+0x87/0x2d0 mm/slub.c:1997
 ___slab_alloc+0xbc5/0x1240 mm/slub.c:3154
 __slab_alloc mm/slub.c:3240 [inline]
 slab_alloc_node mm/slub.c:3325 [inline]
 __kmem_cache_alloc_node+0x126/0x270 mm/slub.c:3398
 __do_kmalloc_node mm/slab_common.c:935 [inline]
 __kmalloc_node+0xa2/0x240 mm/slab_common.c:943
 kmalloc_node include/linux/slab.h:589 [inline]
 kvmalloc_node+0x6c/0x180 mm/util.c:581
 xt_jumpstack_alloc net/netfilter/x_tables.c:1377 [inline]
 xt_replace_table+0x176/0x790 net/netfilter/x_tables.c:1416
 xt_register_table+0x151/0x450 net/netfilter/x_tables.c:1502
 arpt_register_table+0x171/0x690 net/ipv4/netfilter/arp_tables.c:1543
 arptable_filter_table_init+0x3d/0x60 net/ipv4/netfilter/arptable_filter.c:39
 xt_find_table_lock+0x220/0x360 net/netfilter/x_tables.c:1282
 xt_request_find_table_lock+0x22/0x100 net/netfilter/x_tables.c:1307
 get_info net/ipv4/netfilter/arp_tables.c:818 [inline]
 do_arpt_get_ctl+0x686/0x10a0 net/ipv4/netfilter/arp_tables.c:1461
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1487 [inline]
 free_pcp_prepare mm/page_alloc.c:1537 [inline]
 free_unref_page_prepare+0x8e5/0x9e0 mm/page_alloc.c:3414
 free_unref_page+0x2e/0x3f0 mm/page_alloc.c:3509
 free_contig_range+0x9d/0x150 mm/page_alloc.c:9626
 destroy_args+0xef/0xa0e mm/debug_vm_pgtable.c:1031
 debug_vm_pgtable+0x33c/0x38e mm/debug_vm_pgtable.c:1359
 do_one_initcall+0x257/0x800 init/main.c:1309
 do_initcall_level+0x13d/0x1ed init/main.c:1382
 do_initcalls+0x4b/0x8a init/main.c:1398
 kernel_init_freeable+0x401/0x5ab init/main.c:1637
 kernel_init+0x19/0x1b0 init/main.c:1525
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

Memory state around the buggy address:
 ffff88805a556580: fa fb fc fc 00 00 fc fc fa fb fc fc fa fb fc fc
 ffff88805a556600: fb fb fc fc fa fb fc fc 00 00 fc fc 00 00 fc fc
>ffff88805a556680: fa fb fc fc fa fb fc fc fa fb fc fc 00 00 fc fc
                               ^
 ffff88805a556700: 00 00 fc fc fa fb fc fc fa fb fc fc 00 00 fc fc
 ffff88805a556780: 00 04 fc fc 00 05 fc fc 00 07 fc fc 00 06 fc fc
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/03 01:29 linux-6.1.y fb28aa725e05 e611ffe1 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: use-after-free Read in kernfs_find_ns
2026/08/01 21:32 linux-6.1.y fb28aa725e05 e611ffe1 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: use-after-free Read in kernfs_find_ns
* Struck through repros no longer work on HEAD.