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BUG: KASAN: use-after-free in take_option security/selinux/hooks.c:2619 [inline]
BUG: KASAN: use-after-free in selinux_sb_copy_data+0x1cd/0x380 security/selinux/hooks.c:2674
Write of size 10 at addr ffff8801cb208000 by task syz-executor3/7797

CPU: 0 PID: 7797 Comm: syz-executor3 Not tainted 4.9.120-gf85543b #76
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801a2df74c8 ffffffff81eb8049 ffffea00072c8200 ffff8801cb208000
 0000000000000001 ffff8801cb208000 000000000000000a ffff8801a2df7500
 ffffffff8156ab7f ffff8801cb208000 000000000000000a 0000000000000001
Call Trace:
 [<ffffffff81eb8049>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb8049>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff8156ab7f>] print_address_description+0x6c/0x234 mm/kasan/report.c:256
 [<ffffffff8156af89>] kasan_report_error mm/kasan/report.c:355 [inline]
 [<ffffffff8156af89>] kasan_report.cold.6+0x242/0x2fe mm/kasan/report.c:412
 [<ffffffff8153d65f>] check_memory_region_inline mm/kasan/kasan.c:318 [inline]
 [<ffffffff8153d65f>] check_memory_region+0x14f/0x1b0 mm/kasan/kasan.c:325
 [<ffffffff8153dcb7>] memcpy+0x37/0x50 mm/kasan/kasan.c:361
 [<ffffffff81d0cd7d>] take_option security/selinux/hooks.c:2619 [inline]
 [<ffffffff81d0cd7d>] selinux_sb_copy_data+0x1cd/0x380 security/selinux/hooks.c:2674
 [<ffffffff81cee8eb>] security_sb_copy_data+0x7b/0xb0 security/security.c:283
 [<ffffffff8197ef16>] parse_security_options+0x36/0x90 fs/btrfs/super.c:1493
 [<ffffffff8198ff43>] btrfs_mount+0x2f3/0x2bc0 fs/btrfs/super.c:1572
 [<ffffffff8158125c>] mount_fs+0x28c/0x370 fs/super.c:1206
 [<ffffffff815e0b41>] vfs_kern_mount.part.29+0xd1/0x3d0 fs/namespace.c:1000
 [<ffffffff815e0e80>] vfs_kern_mount+0x40/0x60 fs/namespace.c:982
 [<ffffffff8199005b>] mount_subvol fs/btrfs/super.c:1395 [inline]
 [<ffffffff8199005b>] btrfs_mount+0x40b/0x2bc0 fs/btrfs/super.c:1566
 [<ffffffff8158125c>] mount_fs+0x28c/0x370 fs/super.c:1206
 [<ffffffff815e0b41>] vfs_kern_mount.part.29+0xd1/0x3d0 fs/namespace.c:1000
 [<ffffffff815e8369>] vfs_kern_mount fs/namespace.c:982 [inline]
 [<ffffffff815e8369>] do_new_mount fs/namespace.c:2537 [inline]
 [<ffffffff815e8369>] do_mount+0x3c9/0x2740 fs/namespace.c:2859
 [<ffffffff815eb0be>] SYSC_mount fs/namespace.c:3075 [inline]
 [<ffffffff815eb0be>] SyS_mount+0xfe/0x110 fs/namespace.c:3052
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839ffcd3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

The buggy address belongs to the page:
page:ffffea00072c8200 count:0 mapcount:-127 mapping:          (null) index:0xffff8801cb209f80
flags: 0x8000000000000000()
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801cb207f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8801cb207f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8801cb208000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff8801cb208080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8801cb208100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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