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BUG: KASAN: use-after-free in memcpy include/linux/string.h:399 [inline]
BUG: KASAN: use-after-free in memcpy_from_page+0x8c/0x120 lib/iov_iter.c:472
Read of size 4096 at addr ffff888013c45000 by task loop1/14993

CPU: 0 PID: 14993 Comm: loop1 Not tainted 5.10.0-rc1-next-20201028-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xae/0x4c8 mm/kasan/report.c:385
 __kasan_report mm/kasan/report.c:545 [inline]
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:562
 check_memory_region_inline mm/kasan/generic.c:186 [inline]
 check_memory_region+0x13d/0x180 mm/kasan/generic.c:192
 memcpy+0x20/0x60 mm/kasan/common.c:105
 memcpy include/linux/string.h:399 [inline]
 memcpy_from_page+0x8c/0x120 lib/iov_iter.c:472
 iov_iter_copy_from_user_atomic+0x601/0xc60 lib/iov_iter.c:1005
 generic_perform_write+0x277/0x4f0 mm/filemap.c:3405
 __generic_file_write_iter+0x24e/0x610 mm/filemap.c:3526
 generic_file_write_iter+0xd7/0x220 mm/filemap.c:3558
 call_write_iter include/linux/fs.h:1886 [inline]
 do_iter_readv_writev+0x46f/0x740 fs/read_write.c:740
 do_iter_write+0x188/0x670 fs/read_write.c:866
 vfs_iter_write+0x70/0xa0 fs/read_write.c:907
 lo_write_bvec+0x141/0x370 drivers/block/loop.c:287
 lo_write_simple drivers/block/loop.c:309 [inline]
 do_req_filebacked drivers/block/loop.c:632 [inline]
 loop_handle_cmd drivers/block/loop.c:2048 [inline]
 loop_queue_work+0xb33/0x22d0 drivers/block/loop.c:2066
 kthread_worker_fn+0x322/0xce0 kernel/kthread.c:710
 kthread+0x3af/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

The buggy address belongs to the page:
page:000000009ae6070f refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x13c45
flags: 0xfff00000000000()
raw: 00fff00000000000 ffffea0000463648 ffffea000044dc48 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888013c44f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888013c44f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888013c45000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff888013c45080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888013c45100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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