linux-kernel - Re: [PATCH v3 0/3] pstore: add pstore unregister

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Message-ID: <CAGXu5jKjmHGDgQLbipXzz-WXfChXrhYCwW9n+hTGR=-UKN+Dpg@mail.gmail.com>
Date:	Tue, 20 Oct 2015 20:01:20 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Geliang Tang <geliangtang@....com>
Cc:	Anton Vorontsov <anton@...msg.org>,
	Colin Cross <ccross@...roid.com>,
	Tony Luck <tony.luck@...el.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 0/3] pstore: add pstore unregister

On Tue, Oct 20, 2015 at 7:52 PM, Geliang Tang <geliangtang@....com> wrote:
> On Tue, Oct 20, 2015 at 10:19:09AM -0700, Kees Cook wrote:
>> On Tue, Oct 20, 2015 at 12:39 AM, Geliang Tang <geliangtang@....com> wrote:
>> > On Mon, Oct 19, 2015 at 10:56:54PM +0000, Luck, Tony wrote:
>> >> Thanks for looking to close out this TODO item.
>> >>
>> >> The thing that scared me about unloading pstore was what happens to
>> >> a process that is in the middle of reading some /sys/fs/pstore/file-name-here
>>
>> Were you able to verify that this reading-while-rmmod case works correctly?
>>
>> -Kees
>
> $ sudo insmod zlib_deflate.ko
> $ sudo insmod pstore.ko
> $ lsmod
> Module                  Size  Used by
> pstore                 11225  0
> zlib_deflate           18292  1 pstore
>
> $ sudo mount -t pstore pstore /sys/fs/pstore
> $ lsmod
> Module                  Size  Used by
> pstore                 11225  1
> zlib_deflate           18292  1 pstore
>
> $ sudo insmod reed_solomon.ko
> $ sudo insmod ramoops.ko mem_address=0x40000000 mem_size=0x400000
> $ lsmod
> Module                  Size  Used by
> ramoops                 9638  0
> reed_solomon            5150  1 ramoops
> pstore                 11225  2 ramoops
> zlib_deflate           18292  1 pstore
>
> $ tail -f /sys/fs/pstore/console-ramoops-0 &
> [1] 3483
> $ lsmod
> Module                  Size  Used by
> ramoops                 9638  0
> reed_solomon            5150  1 ramoops
> pstore                 11225  3 ramoops
> zlib_deflate           18292  1 pstore
>
> $ kill -9 3483
> $ lsmod
> Module                  Size  Used by
> ramoops                 9638  0
> reed_solomon            5150  1 ramoops
> pstore                 11225  2 ramoops
> zlib_deflate           18292  1 pstore
>
> $ sudo rmmod ramoops
> $ lsmod
> Module                  Size  Used by
> reed_solomon            5150  0
> pstore                 11225  1
> zlib_deflate           18292  1 pstore

What happens if you leave the tail running and try to rmmod ramoops?
(I assume it'll just refuse.)

Nice!

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

>
> $ sudo umount /sys/fs/pstore/
> $ lsmod
> Module                  Size  Used by
> reed_solomon            5150  0
> pstore                 11225  0
> zlib_deflate           18292  1 pstore
>
> $ sudo rmmod pstore
> $ lsmod
> Module                  Size  Used by
> reed_solomon            5150  0
> zlib_deflate           18292  0
>
> Thanks.
> Geliang Tang
>



-- 
Kees Cook
Chrome OS Security
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