KASAN: use-after-free Read in event_handler

Status: upstream: reported C repro on 2026/07/29 00:24
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+3c50f29ba24ea553aab3@syzkaller.appspotmail.com
First crash: 9d16h, last: 7d05h
▶ ▼ Bug presence (1)
Date Name Commit Repro Result
2026/08/05 upstream (ToT) 0d8395707651 C [report] KASAN: slab-use-after-free Read in vhci_shutdown_connection
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 KASAN: use-after-free Read in event_handler 19 syz, C 7 5d12h 10d 0/3 upstream: reported C repro on 2026/07/28 08:51
upstream KASAN: slab-use-after-free Read in event_handler prio:normal usb 19 syz, C error 183 6h43m 199d 0/29 upstream: reported C repro on 2026/01/20 11:33

Sample crash report:
vhci_hcd: stop threads
vhci_hcd: release socket
vhci_hcd: disconnect device
==================================================================
BUG: KASAN: use-after-free in __lock_acquire+0x107/0x7b50 kernel/locking/lockdep.c:4882
Read of size 8 at addr ffff888147da54a8 by task kworker/u4:1/144

CPU: 1 PID: 144 Comm: kworker/u4:1 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: usbip_event event_handler
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 print_address_description+0x60/0x2d0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:434 [inline]
 kasan_report+0xdf/0x130 mm/kasan/report.c:451
 __lock_acquire+0x107/0x7b50 kernel/locking/lockdep.c:4882
 lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5623
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0xb0/0x100 kernel/locking/spinlock.c:162
 unset_event drivers/usb/usbip/usbip_event.c:35 [inline]
 event_handler+0x2a5/0x460 drivers/usb/usbip/usbip_event.c:80
 process_one_work+0x867/0xff0 kernel/workqueue.c:2310
 worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>

Allocated by task 1:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:434 [inline]
 ____kasan_kmalloc mm/kasan/common.c:513 [inline]
 __kasan_kmalloc+0xaf/0xe0 mm/kasan/common.c:522
 kmalloc include/linux/slab.h:612 [inline]
 kzalloc include/linux/slab.h:738 [inline]
 __usb_create_hcd+0x5f/0x830 drivers/usb/core/hcd.c:2587
 vhci_hcd_probe+0xff/0x370 drivers/usb/usbip/vhci_hcd.c:1376
 platform_probe+0x137/0x1c0 drivers/base/platform.c:1391
 call_driver_probe drivers/base/dd.c:-1 [inline]
 really_probe+0x276/0xc70 drivers/base/dd.c:595
 __driver_probe_device+0x1f5/0x390 drivers/base/dd.c:775
 driver_probe_device+0x4f/0x420 drivers/base/dd.c:805
 __device_attach_driver+0x2b0/0x500 drivers/base/dd.c:927
 bus_for_each_drv+0x184/0x210 drivers/base/bus.c:429
 __device_attach+0x2a7/0x480 drivers/base/dd.c:999
 bus_probe_device+0xba/0x1d0 drivers/base/bus.c:489
 device_add+0xbcf/0x1050 drivers/base/core.c:3427
 platform_device_add+0x4bf/0x830 drivers/base/platform.c:712
 vhci_hcd_init+0x3c7/0x500 drivers/usb/usbip/vhci_hcd.c:1571
 do_one_initcall+0x272/0x730 init/main.c:1315
 do_initcall_level+0x13d/0x1f0 init/main.c:1388
 do_initcalls+0x4b/0x90 init/main.c:1404
 kernel_init_freeable+0x3d5/0x560 init/main.c:1628
 kernel_init+0x19/0x1b0 init/main.c:1519
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

Freed by task 4361:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:46
 kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:360
 ____kasan_slab_free+0xd5/0x110 mm/kasan/common.c:366
 kasan_slab_free include/linux/kasan.h:230 [inline]
 slab_free_hook mm/slub.c:1710 [inline]
 slab_free_freelist_hook+0xec/0x170 mm/slub.c:1736
 slab_free mm/slub.c:3504 [inline]
 kfree+0xef/0x2a0 mm/slub.c:4564
 vhci_hcd_remove+0xe0/0x100 drivers/usb/usbip/vhci_hcd.c:1434
 platform_remove+0x92/0xe0 drivers/base/platform.c:1413
 __device_release_driver drivers/base/dd.c:1247 [inline]
 device_release_driver_internal+0x44c/0x710 drivers/base/dd.c:1282
 unbind_store+0x2e2/0x300 drivers/base/bus.c:193
 kernfs_fop_write_iter+0x3a8/0x500 fs/kernfs/file.c:296
 call_write_iter include/linux/fs.h:2173 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x748/0xd70 fs/read_write.c:594
 ksys_write+0x153/0x260 fs/read_write.c:647
 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 ffff888147da4000
 which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 5288 bytes inside of
 8192-byte region [ffff888147da4000, ffff888147da6000)
The buggy address belongs to the page:
page:ffffea00051f6800 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x147da0
head:ffffea00051f6800 order:3 compound_mapcount:0 compound_pincount:0
flags: 0x57ff00000010200(slab|head|node=1|zone=2|lastcpupid=0x7ff)
raw: 057ff00000010200 0000000000000000 dead000000000122 ffff888016c42280
raw: 0000000000000000 0000000000020002 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, ts 9809550787, free_ts 0
 prep_new_page mm/page_alloc.c:2426 [inline]
 get_page_from_freelist+0x24f6/0x2670 mm/page_alloc.c:4192
 __alloc_pages+0x1ee/0x480 mm/page_alloc.c:5501
 alloc_page_interleave+0x24/0x1e0 mm/mempolicy.c:2031
 alloc_slab_page mm/slub.c:1780 [inline]
 allocate_slab mm/slub.c:1917 [inline]
 new_slab+0xc0/0x4b0 mm/slub.c:1980
 ___slab_alloc+0x807/0xdd0 mm/slub.c:3013
 __slab_alloc mm/slub.c:3100 [inline]
 slab_alloc_node mm/slub.c:3191 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 kmem_cache_alloc_trace+0xf9/0x290 mm/slub.c:3250
 kmalloc include/linux/slab.h:607 [inline]
 kzalloc include/linux/slab.h:738 [inline]
 rd_alloc_device+0x6a/0xb0 drivers/target/target_core_rd.c:275
 target_alloc_device+0x9e/0x1390 drivers/target/target_core_device.c:721
 core_dev_setup_virtual_lun0+0xdd/0x210 drivers/target/target_core_device.c:1044
 target_core_init_configfs+0x3b8/0x540 drivers/target/target_core_configfs.c:3638
 do_one_initcall+0x272/0x730 init/main.c:1315
 do_initcall_level+0x13d/0x1f0 init/main.c:1388
 do_initcalls+0x4b/0x90 init/main.c:1404
 kernel_init_freeable+0x3d5/0x560 init/main.c:1628
 kernel_init+0x19/0x1b0 init/main.c:1519
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
page_owner free stack trace missing

Memory state around the buggy address:
 ffff888147da5380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888147da5400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888147da5480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                  ^
 ffff888147da5500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888147da5580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/31 11:54 linux-5.15.y 6e2fd6534337 aaffb173 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in event_handler
2026/07/30 06:51 linux-5.15.y 674f684f7c61 6ef5c1e2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in event_handler
2026/07/29 00:23 linux-5.15.y 674f684f7c61 edc8a875 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in event_handler
* Struck through repros no longer work on HEAD.