Hello, syzbot found the following crash on: HEAD commit: cd234325 usb: gadget: add raw-gadget interface git tree: https://github.com/google/kasan.git usb-fuzzer console output: https://syzkaller.appspot.com/x/log.txt?x=140e49bee00000 kernel config: https://syzkaller.appspot.com/x/.config?x=bb745005307bc641 dashboard link: https://syzkaller.appspot.com/bug?extid=73163a4458e7367880a0 compiler: gcc (GCC) 9.0.0 20181231 (experimental) Unfortunately, I don't have any reproducer for this crash yet. IMPORTANT: if you fix the bug, please add the following tag to the commit: Reported-by: syzbot+73163a4458e7367880a0@xxxxxxxxxxxxxxxxxxxxxxxxx usb 2-1: USB disconnect, device number 45 ================================================================== BUG: KASAN: use-after-free in atomic_fetch_add include/asm-generic/atomic-instrumented.h:111 [inline] BUG: KASAN: use-after-free in refcount_add include/linux/refcount.h:188 [inline] BUG: KASAN: use-after-free in refcount_inc include/linux/refcount.h:228 [inline] BUG: KASAN: use-after-free in get_task_struct include/linux/sched/task.h:113 [inline] BUG: KASAN: use-after-free in kthread_stop+0x90/0x780 kernel/kthread.c:554 Write of size 4 at addr ffff8881ca88e220 by task kworker/0:10/18542 CPU: 0 PID: 18542 Comm: kworker/0:10 Not tainted 5.5.0-rc7-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Workqueue: usb_hub_wq hub_event Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0xef/0x16e lib/dump_stack.c:118 print_address_description.constprop.0.cold+0xd3/0x314 mm/kasan/report.c:374 __kasan_report.cold+0x37/0x85 mm/kasan/report.c:506 kasan_report+0xe/0x20 mm/kasan/common.c:639 check_memory_region_inline mm/kasan/generic.c:185 [inline] check_memory_region+0x152/0x1c0 mm/kasan/generic.c:192 atomic_fetch_add include/asm-generic/atomic-instrumented.h:111 [inline] refcount_add include/linux/refcount.h:188 [inline] refcount_inc include/linux/refcount.h:228 [inline] get_task_struct include/linux/sched/task.h:113 [inline] kthread_stop+0x90/0x780 kernel/kthread.c:554 hwrng_unregister+0x24f/0x330 drivers/char/hw_random/core.c:556 chaoskey_disconnect+0x216/0x290 drivers/usb/misc/chaoskey.c:232 usb_unbind_interface+0x1bd/0x8a0 drivers/usb/core/driver.c:423 __device_release_driver drivers/base/dd.c:1134 [inline] device_release_driver_internal+0x42f/0x500 drivers/base/dd.c:1165 bus_remove_device+0x2eb/0x5a0 drivers/base/bus.c:532 device_del+0x481/0xd30 drivers/base/core.c:2664 usb_disable_device+0x23d/0x790 drivers/usb/core/message.c:1237 usb_disconnect+0x293/0x900 drivers/usb/core/hub.c:2201 hub_port_connect drivers/usb/core/hub.c:5036 [inline] hub_port_connect_change drivers/usb/core/hub.c:5325 [inline] port_event drivers/usb/core/hub.c:5471 [inline] hub_event+0x1a1d/0x4300 drivers/usb/core/hub.c:5553 process_one_work+0x945/0x15c0 kernel/workqueue.c:2264 worker_thread+0x96/0xe20 kernel/workqueue.c:2410 kthread+0x318/0x420 kernel/kthread.c:255 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352 Allocated by task 1824: save_stack+0x1b/0x80 mm/kasan/common.c:72 set_track mm/kasan/common.c:80 [inline] __kasan_kmalloc mm/kasan/common.c:513 [inline] __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:486 slab_post_alloc_hook mm/slab.h:584 [inline] slab_alloc_node mm/slub.c:2759 [inline] kmem_cache_alloc_node+0xdc/0x330 mm/slub.c:2795 alloc_task_struct_node kernel/fork.c:169 [inline] dup_task_struct kernel/fork.c:868 [inline] copy_process+0x43e3/0x6710 kernel/fork.c:1911 _do_fork+0x12d/0xfd0 kernel/fork.c:2421 __do_sys_clone kernel/fork.c:2576 [inline] __se_sys_clone kernel/fork.c:2557 [inline] __x64_sys_clone+0x182/0x210 kernel/fork.c:2557 do_syscall_64+0xb6/0x5a0 arch/x86/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x49/0xbe Freed by task 1824: save_stack+0x1b/0x80 mm/kasan/common.c:72 set_track mm/kasan/common.c:80 [inline] kasan_set_free_info mm/kasan/common.c:335 [inline] __kasan_slab_free+0x117/0x160 mm/kasan/common.c:474 slab_free_hook mm/slub.c:1425 [inline] slab_free_freelist_hook mm/slub.c:1458 [inline] slab_free mm/slub.c:3005 [inline] kmem_cache_free+0x9b/0x360 mm/slub.c:3021 __put_task_struct+0x220/0x510 kernel/fork.c:751 put_task_struct include/linux/sched/task.h:122 [inline] delayed_put_task_struct+0x22a/0x370 kernel/exit.c:182 __rcu_reclaim kernel/rcu/rcu.h:222 [inline] rcu_do_batch kernel/rcu/tree.c:2183 [inline] rcu_core+0x664/0x1e10 kernel/rcu/tree.c:2408 __do_softirq+0x21e/0x950 kernel/softirq.c:292 The buggy address belongs to the object at ffff8881ca88e200 which belongs to the cache task_struct of size 6016 The buggy address is located 32 bytes inside of 6016-byte region [ffff8881ca88e200, ffff8881ca88f980) The buggy address belongs to the page: page:ffffea00072a2200 refcount:1 mapcount:0 mapping:ffff8881da116000 index:0x0 compound_mapcount: 0 raw: 0200000000010200 dead000000000100 dead000000000122 ffff8881da116000 raw: 0000000000000000 0000000000050005 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff8881ca88e100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff8881ca88e180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >ffff8881ca88e200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff8881ca88e280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8881ca88e300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb 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