KASAN: use-after-free Read in do_general_protection

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    62d18ecfa641 Merge tag 'arm64-fixes' of git://git.kernel.o..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13e030d7800000
kernel config:  https://syzkaller.appspot.com/x/.config?x=982e2df1b9e60b02
dashboard link: https://syzkaller.appspot.com/bug?extid=a1264132fc103340628f
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=16b624d7800000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1364e0d7800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a1264132fc103340628f@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: use-after-free in do_general_protection+0x2ac/0x2f0  
arch/x86/kernel/traps.c:538
Read of size 8 at addr ffff8801d7187398 by task syz-executor171/4544

CPU: 0 PID: 4544 Comm: syz-executor171 Not tainted 4.17.0-rc6+ #67
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:

The buggy address belongs to the page:
page:ffffea00075c61c0 count:0 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 0000000000000000 0000000000000000 00000000ffffffff
raw: 0000000000000000 ffffea00075c0101 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d7187280: 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8801d7187300: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ffff8801d7187380: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff8801d7187400: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8801d7187480: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 4544 Comm: syz-executor171 Tainted: G    B              
4.17.0-rc6+ #67
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


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