Re: KASAN: use-after-free Read in do_general_protection

[Dmitry Vyukov]

On Sat, May 26, 2018 at 11:16 AM, syzbot
<syzbot+a1264132fc103340628f@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> 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..


Dups of this bug:

KASAN: stack-out-of-bounds Read in do_general_protection
KASAN: slab-out-of-bounds Read in vmx_vcpu_run
KASAN: use-after-scope Read in vmx_vcpu_run
KASAN: stack-out-of-bounds Write in notify_die

See full info at:
https://syzkaller.appspot.com/bug?extid=a1264132fc103340628f


There seems to be 2 problems:

1. msr_write_intercepted doing something notoriously bad.

2. general_protection fault handler somehow allocates pt_regs
overlapping with vmx_run frame. This can be an issue with interrupts
too.


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