linux-kernel - Re: [PATCH AUTOSEL 4.19 104/123] pstore/ram: Correctly calculate usable PRZ bytes

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Date:   Wed, 12 Dec 2018 18:14:41 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     "# 3.4.x" <stable@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH AUTOSEL 4.19 104/123] pstore/ram: Correctly calculate
 usable PRZ bytes

On Wed, Dec 05, 2018 at 02:57:08PM -0800, Kees Cook wrote:
>On Wed, Dec 5, 2018 at 1:41 AM Sasha Levin <sashal@...nel.org> wrote:
>>
>> From: Kees Cook <keescook@...omium.org>
>>
>> [ Upstream commit 89d328f637b9904b6d4c9af73c8a608b8dd4d6f8 ]
>>
>> The actual number of bytes stored in a PRZ is smaller than the
>> bytes requested by platform data, since there is a header on each
>> PRZ. Additionally, if ECC is enabled, there are trailing bytes used
>> as well. Normally this mismatch doesn't matter since PRZs are circular
>> buffers and the leading "overflow" bytes are just thrown away. However, in
>> the case of a compressed record, this rather badly corrupts the results.
>>
>> This corruption was visible with "ramoops.mem_size=204800 ramoops.ecc=1".
>> Any stored crashes would not be uncompressable (producing a pstorefs
>> "dmesg-*.enc.z" file), and triggering errors at boot:
>>
>>   [    2.790759] pstore: crypto_comp_decompress failed, ret = -22!
>>
>> Backporting this depends on commit 70ad35db3321 ("pstore: Convert console
>> write to use ->write_buf")
>
>Please note the above. If this gets backported, this one is needed too.

Okay, I've added 70ad35db3321 for 4.9, 4.4, and 3.18.

--
Thanks,
Sasha