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BUG: KASAN: use-after-free in _copy_to_user+0x9d/0xd0 lib/usercopy.c:27
Read of size 976 at addr ffff88818b7ffff2 by task syz-executor.5/15765

CPU: 0 PID: 15765 Comm: syz-executor.5 Not tainted 4.14.140+ #39
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0xca/0x134 lib/dump_stack.c:53
 print_address_description+0x60/0x226 mm/kasan/report.c:187
 __kasan_report.cold+0x1a/0x41 mm/kasan/report.c:316
 _copy_to_user+0x9d/0xd0 lib/usercopy.c:27
 copy_to_user include/linux/uaccess.h:155 [inline]
 bpf_test_finish.isra.0+0xa7/0x160 net/bpf/test_run.c:59
 bpf_prog_test_run_skb+0x528/0x8c0 net/bpf/test_run.c:144
 bpf_prog_test_run kernel/bpf/syscall.c:1346 [inline]
 SYSC_bpf kernel/bpf/syscall.c:1618 [inline]
 SyS_bpf+0xa3b/0x3830 kernel/bpf/syscall.c:1563
 do_syscall_64+0x19b/0x520 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x459879
RSP: 002b:00007fcab7e78c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459879
RDX: 0000000000000028 RSI: 0000000020000140 RDI: 000000000000000a
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fcab7e796d4
R13: 00000000004bfbf2 R14: 00000000004d18b8 R15: 00000000ffffffff

The buggy address belongs to the page:
page:ffffea00062dffc0 count:0 mapcount:0 mapping:          (null) index:0x0
flags: 0x4000000000000000()
raw: 4000000000000000 0000000000000000 0000000000000000 00000000ffffffff
raw: dead000000000100 dead000000000200 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88818b7ffe80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88818b7fff00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88818b7fff80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                             ^
 ffff88818b800000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88818b800080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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