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BUG: KASAN: stack-out-of-bounds in iov_iter_advance+0x4b3/0x4f0 lib/iov_iter.c:491
Read of size 8 at addr ffff8801d7537d60 by task syz-executor.4/4119

CPU: 1 PID: 4119 Comm: syz-executor.4 Not tainted 4.4.174+ #4
 0000000000000000 9c7734465298ca8f ffff8801d7537a10 ffffffff81aad1a1
 0000000000000000 ffffea00075d4dc0 ffff8801d7537d60 0000000000000008
 ffff8801d7537d58 ffff8801d7537a48 ffffffff81490120 0000000000000000
Call Trace:
 [<ffffffff81aad1a1>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81aad1a1>] dump_stack+0xc1/0x120 lib/dump_stack.c:51
 [<ffffffff81490120>] print_address_description+0x6f/0x21b mm/kasan/report.c:252
 [<ffffffff81490358>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff81490358>] kasan_report mm/kasan/report.c:408 [inline]
 [<ffffffff81490358>] kasan_report.cold+0x8c/0x2be mm/kasan/report.c:393
 [<ffffffff81484ed4>] __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:429
 [<ffffffff81ae82f3>] iov_iter_advance+0x4b3/0x4f0 lib/iov_iter.c:491
 [<ffffffff81e22476>] tun_get_user+0x2c6/0x2640 drivers/net/tun.c:1124
 [<ffffffff81e24a0a>] tun_chr_write_iter+0xda/0x190 drivers/net/tun.c:1283
 [<ffffffff81496ae8>] new_sync_write fs/read_write.c:480 [inline]
 [<ffffffff81496ae8>] __vfs_write+0x2e8/0x3d0 fs/read_write.c:493
 [<ffffffff81498612>] vfs_write+0x182/0x4e0 fs/read_write.c:540
 [<ffffffff8149ac4c>] SYSC_write fs/read_write.c:587 [inline]
 [<ffffffff8149ac4c>] SyS_write+0xdc/0x1c0 fs/read_write.c:579
 [<ffffffff82718ba1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

The buggy address belongs to the page:
page:ffffea00075d4dc0 count:0 mapcount:0 mapping:          (null) index:0x0
flags: 0x4000000000000000()
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d7537c00: f2 f2 f2 f2 f2 00 00 00 00 00 00 00 f3 f3 f3 f3
 ffff8801d7537c80: f3 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8801d7537d00: 00 00 00 00 00 f1 f1 f1 f1 00 00 f2 f2 00 00 00
                                                       ^
 ffff8801d7537d80: 00 00 f2 f2 f2 f2 f2 00 00 00 00 00 f3 f3 f3 f3
 ffff8801d7537e00: f3 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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