==================================================================
BUG: KASAN: use-after-free in memcpy syzkaller/managers/linux-4-14/kernel/./include/linux/string.h:372 [inline]
BUG: KASAN: use-after-free in memcpy_from_page+0x8c/0x110 syzkaller/managers/linux-4-14/kernel/lib/iov_iter.c:453
Read of size 4096 at addr ffff8880a2181000 by task loop0/3290

CPU: 0 PID: 3290 Comm: loop0 Not tainted 4.14.218-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack syzkaller/managers/linux-4-14/kernel/lib/dump_stack.c:17 [inline]
 dump_stack+0x1b2/0x281 syzkaller/managers/linux-4-14/kernel/lib/dump_stack.c:58
 print_address_description.cold+0x54/0x1d3 syzkaller/managers/linux-4-14/kernel/mm/kasan/report.c:252
 kasan_report_error.cold+0x8a/0x191 syzkaller/managers/linux-4-14/kernel/mm/kasan/report.c:351
 kasan_report+0x6f/0x80 syzkaller/managers/linux-4-14/kernel/mm/kasan/report.c:409
 memcpy+0x20/0x50 syzkaller/managers/linux-4-14/kernel/mm/kasan/kasan.c:302
 memcpy syzkaller/managers/linux-4-14/kernel/./include/linux/string.h:372 [inline]
 memcpy_from_page+0x8c/0x110 syzkaller/managers/linux-4-14/kernel/lib/iov_iter.c:453
 iov_iter_copy_from_user_atomic+0x594/0x930 syzkaller/managers/linux-4-14/kernel/lib/iov_iter.c:799
 generic_perform_write+0x21f/0x420 syzkaller/managers/linux-4-14/kernel/mm/filemap.c:3063
 __generic_file_write_iter+0x227/0x590 syzkaller/managers/linux-4-14/kernel/mm/filemap.c:3180
 generic_file_write_iter+0x36f/0x650 syzkaller/managers/linux-4-14/kernel/mm/filemap.c:3208
 call_write_iter syzkaller/managers/linux-4-14/kernel/./include/linux/fs.h:1778 [inline]
 do_iter_readv_writev+0x4cf/0x5f0 syzkaller/managers/linux-4-14/kernel/fs/read_write.c:675
 do_iter_write+0x152/0x550 syzkaller/managers/linux-4-14/kernel/fs/read_write.c:954
 vfs_iter_write+0x70/0xa0 syzkaller/managers/linux-4-14/kernel/fs/read_write.c:967
 lo_write_bvec+0x114/0x310 syzkaller/managers/linux-4-14/kernel/drivers/block/loop.c:272
 lo_write_simple syzkaller/managers/linux-4-14/kernel/drivers/block/loop.c:294 [inline]
 do_req_filebacked syzkaller/managers/linux-4-14/kernel/drivers/block/loop.c:587 [inline]
 loop_handle_cmd syzkaller/managers/linux-4-14/kernel/drivers/block/loop.c:1779 [inline]
 loop_queue_work+0x922/0x1e80 syzkaller/managers/linux-4-14/kernel/drivers/block/loop.c:1793
 kthread_worker_fn+0x271/0x6c0 syzkaller/managers/linux-4-14/kernel/kernel/kthread.c:642
 kthread+0x30d/0x420 syzkaller/managers/linux-4-14/kernel/kernel/kthread.c:232
 ret_from_fork+0x24/0x30 syzkaller/managers/linux-4-14/kernel/arch/x86/entry/entry_64.S:404

The buggy address belongs to the page:
page:ffffea0002886040 count:0 mapcount:0 mapping:          (null) index:0x0
flags: 0xfff00000000000()
raw: 00fff00000000000 0000000000000000 0000000000000000 00000000ffffffff
raw: ffffea0002ace220 ffffea00026f1f60 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880a2180f00: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff8880a2180f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8880a2181000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff8880a2181080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880a2181100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================