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BUG: KASAN: use-after-free in soft_cursor+0x95a/0xa20 drivers/video/fbdev/core/softcursor.c:61
Read of size 1 at addr ffff88804d52b470 by task kworker/0:3/7448

CPU: 0 PID: 7448 Comm: kworker/0:3 Not tainted 4.19.118-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_power_efficient fb_flashcursor
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x188/0x20d lib/dump_stack.c:118
 print_address_description.cold+0x7c/0x212 mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report mm/kasan/report.c:412 [inline]
 kasan_report.cold+0x88/0x2b9 mm/kasan/report.c:396
 soft_cursor+0x95a/0xa20 drivers/video/fbdev/core/softcursor.c:61
 bit_cursor+0x1230/0x1900 drivers/video/fbdev/core/bitblit.c:386
 fb_flashcursor+0x396/0x440 drivers/video/fbdev/core/fbcon.c:399
 process_one_work+0x91f/0x1640 kernel/workqueue.c:2155
 worker_thread+0x96/0xe20 kernel/workqueue.c:2298
 kthread+0x34a/0x420 kernel/kthread.c:246
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

Allocated by task 25555:
 set_track mm/kasan/kasan.c:460 [inline]
 kasan_kmalloc mm/kasan/kasan.c:553 [inline]
 kasan_kmalloc+0xbf/0xe0 mm/kasan/kasan.c:531
 __do_kmalloc_node mm/slab.c:3689 [inline]
 __kmalloc_node+0x4c/0x70 mm/slab.c:3696
 kmalloc_node include/linux/slab.h:557 [inline]
 kzalloc_node include/linux/slab.h:720 [inline]
 qdisc_alloc+0xb6/0xa40 net/sched/sch_generic.c:836
 qdisc_create_dflt+0x70/0x1d0 net/sched/sch_generic.c:910
 mq_init+0x363/0x4b0 net/sched/sch_mq.c:95
 qdisc_create_dflt+0xff/0x1d0 net/sched/sch_generic.c:917
 attach_default_qdiscs net/sched/sch_generic.c:1056 [inline]
 dev_activate+0x8c1/0xb30 net/sched/sch_generic.c:1095
 __dev_open+0x265/0x390 net/core/dev.c:1415
 __dev_change_flags+0x4dd/0x620 net/core/dev.c:7666
 dev_change_flags+0x7e/0x140 net/core/dev.c:7735
 dev_ifsioc+0x286/0x8d0 net/core/dev_ioctl.c:237
 dev_ioctl+0x1ab/0xc58 net/core/dev_ioctl.c:488
 sock_do_ioctl+0x1b7/0x2f0 net/socket.c:973
 sock_ioctl+0x325/0x610 net/socket.c:1074
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0xcda/0x12e0 fs/ioctl.c:688
 ksys_ioctl+0x9b/0xc0 fs/ioctl.c:705
 __do_sys_ioctl fs/ioctl.c:712 [inline]
 __se_sys_ioctl fs/ioctl.c:710 [inline]
 __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:710
 do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 25543:
 set_track mm/kasan/kasan.c:460 [inline]
 __kasan_slab_free+0xf7/0x140 mm/kasan/kasan.c:521
 __cache_free mm/slab.c:3503 [inline]
 kfree+0xce/0x220 mm/slab.c:3822
 qdisc_destroy+0x4aa/0x6b0 net/sched/sch_generic.c:997
 shutdown_scheduler_queue net/sched/sch_generic.c:1291 [inline]
 netdev_for_each_tx_queue include/linux/netdevice.h:2107 [inline]
 dev_shutdown+0x11e/0x47a net/sched/sch_generic.c:1297
 rollback_registered_many+0x64a/0xc40 net/core/dev.c:8176
 rollback_registered+0xf2/0x1c0 net/core/dev.c:8225
 unregister_netdevice_queue net/core/dev.c:9278 [inline]
 unregister_netdevice_queue+0x1d7/0x2b0 net/core/dev.c:9271
 unregister_netdevice include/linux/netdevice.h:2614 [inline]
 __tun_detach+0xd86/0x1020 drivers/net/tun.c:737
 tun_detach drivers/net/tun.c:754 [inline]
 tun_chr_close+0xd9/0x180 drivers/net/tun.c:3261
 __fput+0x2cd/0x890 fs/file_table.c:278
 task_work_run+0x13f/0x1b0 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:193 [inline]
 exit_to_usermode_loop+0x25a/0x2b0 arch/x86/entry/common.c:167
 prepare_exit_to_usermode arch/x86/entry/common.c:198 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:271 [inline]
 do_syscall_64+0x538/0x620 arch/x86/entry/common.c:296
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff88804d52ae80
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1520 bytes inside of
 2048-byte region [ffff88804d52ae80, ffff88804d52b680)
The buggy address belongs to the page:
page:ffffea0001354a80 count:1 mapcount:0 mapping:ffff88812c39cc40 index:0x0 compound_mapcount: 0
flags: 0xfffe0000008100(slab|head)
raw: 00fffe0000008100 ffffea00021a2888 ffffea000073e688 ffff88812c39cc40
raw: 0000000000000000 ffff88804d52a600 0000000100000003 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88804d52b300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88804d52b380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88804d52b400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                             ^
 ffff88804d52b480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88804d52b500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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