KASAN: global-out-of-bounds Read in mqueue_get_tree

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    7c1b097f27bf Add linux-next specific files for 20180912
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=152fcd49400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5980033172920ec0
dashboard link: https://syzkaller.appspot.com/bug?extid=8a81fb3d40f8c58aa8e2
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=140a53da400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10b0c6ae400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+8a81fb3d40f8c58aa8e2@xxxxxxxxxxxxxxxxxxxxxxxxx

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
==================================================================
BUG: KASAN: global-out-of-bounds in mqueue_get_tree+0x2a2/0x2e0  
ipc/mqueue.c:362
Read of size 8 at addr ffffffff885cef68 by task syz-executor013/5545

CPU: 0 PID: 5545 Comm: syz-executor013 Not tainted  
4.19.0-rc3-next-20180912+ #72
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1d3/0x2c4 lib/dump_stack.c:113
 print_address_description.cold.8+0x58/0x1ff mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
 mqueue_get_tree+0x2a2/0x2e0 ipc/mqueue.c:362
 vfs_get_tree+0x1cb/0x5c0 fs/super.c:1787
 mq_create_mount+0xe3/0x190 ipc/mqueue.c:415
 mq_init_ns+0x15a/0x210 ipc/mqueue.c:1621
 create_ipc_ns ipc/namespace.c:58 [inline]
 copy_ipcs+0x3d2/0x580 ipc/namespace.c:84
 create_new_namespaces+0x376/0x900 kernel/nsproxy.c:87
 unshare_nsproxy_namespaces+0xc3/0x1f0 kernel/nsproxy.c:206
 ksys_unshare+0x79c/0x10b0 kernel/fork.c:2535
 __do_sys_unshare kernel/fork.c:2603 [inline]
 __se_sys_unshare kernel/fork.c:2601 [inline]
 __x64_sys_unshare+0x31/0x40 kernel/fork.c:2601
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x446257
Code: 00 00 00 b8 63 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 dd d7 fb ff c3  
66 2e 0f 1f 84 00 00 00 00 00 66 90 b8 10 01 00 00 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 bd d7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffe2677e8e8 EFLAGS: 00000217 ORIG_RAX: 0000000000000110
RAX: ffffffffffffffda RBX: 00007ffe2677f450 RCX: 0000000000446257
RDX: 0000000000000000 RSI: 00007ffe2677e8f0 RDI: 0000000008000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000018
R10: 0000000000000000 R11: 0000000000000217 R12: 0000000000403ea0
R13: 0000000000403f30 R14: 0000000000000000 R15: 0000000000000000

The buggy address belongs to the variable:
 ipcns_operations+0x68/0xa00

Memory state around the buggy address:
 ffffffff885cee00: fa fa fa fa 00 00 00 00 00 02 fa fa fa fa fa fa
 ffffffff885cee80: 00 00 00 01 fa fa fa fa 04 fa fa fa fa fa fa fa
> ffffffff885cef00: 00 00 00 00 00 00 00 00 fa fa fa fa 03 fa fa fa
                                                          ^
 ffffffff885cef80: fa fa fa fa 07 fa fa fa fa fa fa fa 00 03 fa fa
 ffffffff885cf000: fa fa fa fa 00 fa fa fa fa fa fa fa 00 04 fa fa
==================================================================


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