From: Kees Cook <keescook@chromium.org>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Anton Vorontsov <anton@enomsg.org>,
Colin Cross <ccross@android.com>, Tony Luck <tony.luck@intel.com>
Subject: Re: [PATCH 8/8] pstore/ram: Correctly calculate usable PRZ bytes
Date: Mon, 5 Nov 2018 09:04:13 -0800 [thread overview]
Message-ID: <CAGXu5jJzszbMOZAj_K0tfBV-3Rs67_gedHd+RwSXvzY38Fu3dA@mail.gmail.com> (raw)
In-Reply-To: <20181105044217.GB56850@google.com>
On Sun, Nov 4, 2018 at 8:42 PM, Joel Fernandes <joel@joelfernandes.org> wrote:
> Dumping the magic bytes of the non decompressable .enc.z files, I get this
> which shows a valid zlib compressed header:
>
> Something like:
> 48 89 85 54 4d 6f 1a 31
>
> The 0b1000 in the first byte means it is "deflate". The file tool indeed
> successfully shows "zlib compressed data" and I did the math for the header
> and it is indeed valid. So I don't think the data is insane. The buffer has
> enough room because even the very small dumps are not decompressable.
Interesting. So the kernel wouldn't decompress it even though it's the
right algo and untruncated? That seems worth fixing.
> At this point we can park this issue I guess, but a scenario that is still
> broken is:
> Say someone crashes the system on compress algo X and then recompiles with
> compress algo Y, then the decompress would fail no?
>
> One way to fix that is to store the comrpession method in buffer as well,
> then initialize all algorithms at boot and choose the right one in the
> buffer ideally. Otherwise atleast we should print a message saying "buffer is
> encoded with algo X but compression selected is Y" or something. But I agree
> its a very low priority "doctor it hurts if I do this" kind of issue :)
Right, this is fine: if algos change across a kernel version, I'm fine
with it failing. pstore isn't expected to work sanely outside of a
pretty narrow set of use-cases.
-Kees
--
Kees Cook
next prev parent reply other threads:[~2018-11-05 17:04 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-01 23:51 [PATCH 0/8] pstore improvements (pstore-next) Kees Cook
2018-11-01 23:51 ` [PATCH linux-next 1/8] pstore/ram: Standardize module name in ramoops Kees Cook
2018-11-01 23:51 ` [PATCH 2/8] pstore: Do not use crash buffer for decompression Kees Cook
2018-11-02 18:24 ` Joel Fernandes
2018-11-14 7:56 ` Kees Cook
2018-11-20 21:43 ` Joel Fernandes
2018-11-29 22:06 ` Kees Cook
2018-11-30 2:26 ` Joel Fernandes
2018-11-01 23:51 ` [PATCH 3/8] pstore/ram: Report backend assignments with finer granularity Kees Cook
2018-11-01 23:51 ` [PATCH 4/8] pstore/ram: Add kern-doc for struct persistent_ram_zone Kees Cook
2018-11-01 23:51 ` [PATCH 5/8] pstore: Improve and update some comments and status output Kees Cook
2018-11-01 23:51 ` [PATCH 6/8] pstore: Replace open-coded << with BIT() Kees Cook
2018-11-01 23:51 ` [PATCH 7/8] pstore: Remove needless lock during console writes Kees Cook
2018-11-02 18:32 ` Joel Fernandes
2018-11-02 20:40 ` Kees Cook
2018-11-02 21:50 ` Joel Fernandes
2018-11-01 23:52 ` [PATCH 8/8] pstore/ram: Correctly calculate usable PRZ bytes Kees Cook
2018-11-02 18:01 ` Joel Fernandes
2018-11-02 20:00 ` Kees Cook
2018-11-05 4:42 ` Joel Fernandes
2018-11-05 17:04 ` Kees Cook [this message]
2018-11-06 4:42 ` Joel Fernandes
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