linux-kernel - Re: [PATCH 0/2] of: overlay: Crash fix and improvement

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Date:   Sat, 9 Dec 2017 10:04:48 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Frank Rowand <frowand.list@...il.com>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Rob Herring <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] of: overlay: Crash fix and improvement

Hi Frank,

On Sat, Dec 9, 2017 at 7:01 AM, Frank Rowand <frowand.list@...il.com> wrote:
> On 12/08/17 05:13, Geert Uytterhoeven wrote:
>> This patch series fixes memory corruption when applying overlays.
>> I first noticed this when using OF configfs.  After lots of failed
>> debugging attempts, I bisected it to "of: overlay: add per overlay sysfs
>> attributes", which is not upstream.  But that was a red herring: that
>> commit enlarged struct fragment to exactly 64-bytes, which just made it
>> more likely to cause random corruption when writing beyond the end of an
>> array of fragment structures.  With the smaller structure size before,
>> such writes usually ended up in the unused holes between allocated
>> blocks, causing no harm.
>>
>> The first patch is the real fix, and applies to both v4.15-rc2 and Rob's
>> for-next branch.
>> The second patch is a small improvement, and applies to Rob's for-next
>> branch only.
>
> Overlay FDT files should not have invalid contents.  But they inevitably
> will, so the code has to handle those cases.  Thanks for finding this
> problem and making the code better!

Sure, people can throw anything at it ;-)

In my case, I'm wondering if the dtbo was actually invalid?
Simplification of the decompiled dtbo:

/dts-v1/;

/ {

        fragment-name {
                target-path = [2f 00];

                __overlay__ {

                        node-name {
                                compatible = "foo,bar";
                                gpios = <0xffffffff 0x0 0x0>;
                        };
                };
        };

        __fixups__ {
                bank0 = "/fragment-name/__overlay__/node-name:gpios:0";
        };
};

So it has __fixup__, but no __symbols__, which looks totally valid to me.

> For the full series:
>
> Reviewed-by: Frank Rowand <frank.rowand@...y.com>

Thanks!

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds