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BUG: KASAN: use-after-free in ex_handler_refcount+0x18f/0x1c0 arch/x86/mm/extable.c:49
Write of size 4 at addr ffff88809fff5358 by task kworker/1:2/3388

CPU: 1 PID: 3388 Comm: kworker/1:2 Not tainted 4.19.128-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events do_enable_set
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1fc/0x2fe lib/dump_stack.c:118
 print_address_description.cold+0x54/0x222 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
 ex_handler_refcount+0x18f/0x1c0 arch/x86/mm/extable.c:49
 fixup_exception+0x8a/0xc3 arch/x86/mm/extable.c:197
 do_trap_no_signal arch/x86/kernel/traps.c:209 [inline]
 do_trap+0x61/0x250 arch/x86/kernel/traps.c:258
 do_error_trap+0x15d/0x310 arch/x86/kernel/traps.c:303
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:1038
RIP: 0010:csum_partial_copy_generic+0x609e/0x7842
Code: 49 8d 8c 24 80 00 00 00 0f 0b 48 8d 8d 80 00 00 00 0f 0b 48 8d 8d 80 00 00 00 0f 0b 49 8d 8c 24 b8 02 00 00 0f 0b 48 8d 4d 18 <0f> 0b 48 8d 8d b8 02 00 00 0f 0b 48 8d 4b 18 0f 0b 48 8d 8d 80 00
RSP: 0018:ffff88809b327c38 EFLAGS: 00010297
RAX: ffff88809b31c640 RBX: 0000000000000000 RCX: ffff88809fff5358
RDX: 0000000000000000 RSI: ffffffff8663f320 RDI: ffff88809fff5340
RBP: ffff88809fff5340 R08: ffff88809b31c640 R09: fffffbfff12e2e59
R10: fffffbfff12e2e58 R11: ffffffff897172c3 R12: ffff88809b327cc0
R13: ffff88809f2edc00 R14: ffff88809b327cc0 R15: ffff88809b327cc0
 do_enable_set+0x4d1/0x8d0 net/bluetooth/6lowpan.c:1087
 process_one_work+0x892/0x1580 kernel/workqueue.c:2155
 worker_thread+0x96/0xe20 kernel/workqueue.c:2298
 kthread+0x30b/0x410 kernel/kthread.c:246
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

Allocated by task 3388:
 kmem_cache_alloc_trace+0x14b/0x3a0 mm/slab.c:3625
 kmalloc include/linux/slab.h:515 [inline]
 kzalloc include/linux/slab.h:709 [inline]
 l2cap_chan_create+0x40/0x380 net/bluetooth/l2cap_core.c:441
 chan_create+0xc/0xd0 net/bluetooth/6lowpan.c:652
 bt_6lowpan_listen net/bluetooth/6lowpan.c:971 [inline]
 do_enable_set+0x507/0x8d0 net/bluetooth/6lowpan.c:1090
 process_one_work+0x892/0x1580 kernel/workqueue.c:2155
 worker_thread+0x96/0xe20 kernel/workqueue.c:2298
 kthread+0x30b/0x410 kernel/kthread.c:246
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

Freed by task 7221:
 __cache_free mm/slab.c:3503 [inline]
 kfree+0xce/0x220 mm/slab.c:3822
 l2cap_chan_destroy net/bluetooth/l2cap_core.c:479 [inline]
 kref_put include/linux/kref.h:70 [inline]
 l2cap_chan_put+0x16b/0x1c0 net/bluetooth/l2cap_core.c:493
 do_enable_set+0x4d1/0x8d0 net/bluetooth/6lowpan.c:1087
 process_one_work+0x892/0x1580 kernel/workqueue.c:2155
 worker_thread+0x96/0xe20 kernel/workqueue.c:2298
 kthread+0x30b/0x410 kernel/kthread.c:246
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

The buggy address belongs to the object at ffff88809fff5340
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 24 bytes inside of
 2048-byte region [ffff88809fff5340, ffff88809fff5b40)
The buggy address belongs to the page:
page:ffffea00027ffd00 count:1 mapcount:0 mapping:ffff88812c3dcc40 index:0x0 compound_mapcount: 0
flags: 0xfffe0000008100(slab|head)
raw: 00fffe0000008100 ffffea0002829288 ffffea00027b4d08 ffff88812c3dcc40
raw: 0000000000000000 ffff88809fff4240 0000000100000003 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88809fff5200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88809fff5280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88809fff5300: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                                    ^
 ffff88809fff5380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88809fff5400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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