linux-kernel - Re: KASAN: slab-out-of-bounds Write in tty_insert_flip_string_fixed

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Date:   Wed, 25 Apr 2018 22:02:24 +0900
From:   DaeRyong Jeong <threeearcat@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Byoungyoung Lee <byoungyoung@...due.edu>,
        Kyungtae Kim <kt0755@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, basavesh@...due.edu
Subject: Re: KASAN: slab-out-of-bounds Write in tty_insert_flip_string_fixed_flag

I'm really sorry for you to wait.
Since I made a few mistakes previously, I really don't want to make a
mistake again.
Therefore I have been reading documents more carefully and learning
the approved email client (i.e., mutt).
It is almost done. I will send a patch very soon.

Again, I'm really sorry.

Best regards,
Daeryong Jeong.

On Wed, Apr 25, 2018 at 9:53 PM, Greg KH <gregkh@...uxfoundation.org> wrote:
> On Thu, Apr 19, 2018 at 09:25:08PM +0900, DaeRyong Jeong wrote:
>> The patch is attached at the end of this email and can be downloaded from here.
>> https://kiwi.cs.purdue.edu/static/race-fuzzer/tty_insert_flip_string_fixed_flag.patch
>>
>> We applied the patch to v4.16 and tested our reproducer. we can't see the
>> crash any longer.
>>
>> Our rationale is
>>   - Since tty_wakeup() called by __start_tty() sends frames, call
>>     tty_write_lock() before __start_tty().
>>   - Since tty_write_lock() might sleep, locate tty_write_lock() before
>>     spin_lock_irq(&tty->flow_lock).
>>   - Since wake_up_interruptible_poll() is called by both tty_write_unlock()
>>     and __start_tty(), Prevent calling wake_up_interruptible_poll() twice by
>>     adding the wakeup flag to tty_write_unlock()
>>
>> If there is something that we are missing or we are wrong, please let us know.
>>
>>
>> Thank you.
>>
>> Best regards,
>> Daeryong Jeong
>>
>>
>>
>> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
>> index 63114ea..09c76d3 100644
>> --- a/drivers/tty/tty_io.c
>> +++ b/drivers/tty/tty_io.c
>> @@ -873,13 +873,15 @@ static ssize_t tty_read(struct file *file, char
>> __user *buf, size_t count,
>>   return i;
>>  }
>>
>> -static void tty_write_unlock(struct tty_struct *tty)
>> +void tty_write_unlock(struct tty_struct *tty, int wakeup)
>>  {
>>   mutex_unlock(&tty->atomic_write_lock);
>> - wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
>> + if (wakeup) {
>> + wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
>> + }
>>  }
>>
>
> <snip>
>
> What ever happened to this patch, did you end up resending it in a
> non-corrupted way?
>
> thanks,
>
> greg k-h