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BUG: KASAN: use-after-free in memcpy include/linux/fortify-string.h:191 [inline]
BUG: KASAN: use-after-free in memcpy_from_page include/linux/highmem.h:321 [inline]
BUG: KASAN: use-after-free in iov_iter_copy_from_user_atomic+0x7ea/0xc50 lib/iov_iter.c:991
Read of size 4096 at addr ffff888020736000 by task loop0/2226

CPU: 0 PID: 2226 Comm: loop0 Not tainted 5.12.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x141/0x1d7 lib/dump_stack.c:120
 print_address_description.constprop.0.cold+0x5b/0x2c6 mm/kasan/report.c:232
 __kasan_report mm/kasan/report.c:399 [inline]
 kasan_report.cold+0x7c/0xd8 mm/kasan/report.c:416
 check_region_inline mm/kasan/generic.c:180 [inline]
 kasan_check_range+0x13d/0x180 mm/kasan/generic.c:186
 memcpy+0x20/0x60 mm/kasan/shadow.c:65
 memcpy include/linux/fortify-string.h:191 [inline]
 memcpy_from_page include/linux/highmem.h:321 [inline]
 iov_iter_copy_from_user_atomic+0x7ea/0xc50 lib/iov_iter.c:991
 generic_perform_write+0x277/0x4f0 mm/filemap.c:3583
 __generic_file_write_iter+0x24e/0x610 mm/filemap.c:3704
 generic_file_write_iter+0xd7/0x220 mm/filemap.c:3736
 call_write_iter include/linux/fs.h:1977 [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+0x141/0x6c0 drivers/block/loop.c:284
 lo_write_simple drivers/block/loop.c:306 [inline]
 do_req_filebacked drivers/block/loop.c:629 [inline]
 loop_handle_cmd drivers/block/loop.c:2045 [inline]
 loop_queue_work+0xb70/0x1fb0 drivers/block/loop.c:2063
 kthread_worker_fn+0x322/0xcf0 kernel/kthread.c:735
 kthread+0x3b1/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

The buggy address belongs to the page:
page:ffffea000081cd80 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x20736
flags: 0xfff00000000000()
raw: 00fff00000000000 ffffea00009fb7c8 ffffea00008bb4c8 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888020735f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc
 ffff888020735f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888020736000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
                   ^
 ffff888020736080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888020736100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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