On 12/05/17 05:49, Geert Uytterhoeven wrote:
> Hi Frank,
>
> On Tue, Dec 5, 2017 at 9:01 AM, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
>> On Tue, Dec 5, 2017 at 3:07 AM, Frank Rowand <frowand.list@xxxxxxxxx> wrote:
>>> On 12/04/17 10:47, Geert Uytterhoeven wrote:
>>>> If of_resolve_phandles() fails, free_overlay_changeset() is called in
>>>> the error path. However, that function returns early if the list hasn't
>>>> been initialized yet, before freeing the object.
>>>>
>>>> Explicitly calling kfree() instead would solve that issue. However, that
>>>> complicates matter, by having to consider which of two different methods
>>>> to use to dispose of the same object.
>>>>
>>>> Hence make free_overlay_changeset() consider initialization state of the
>>>> different parts of the object, making it always safe to call (once!) to
>>>> dispose of a (partially) initialized overlay_changeset:
>>>> - Only destroy the changeset if the list was initialized,
>>>> - Ignore uninitialized IDs (zero).
>>>>
>>>> Reported-by: Colin King <colin.king@xxxxxxxxxxxxx>
>>>> Fixes: f948d6d8b792bb90 ("of: overlay: avoid race condition between applying multiple overlays")
>>>> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
>>>> ---
>>>> drivers/of/overlay.c | 7 +++----
>>>> 1 file changed, 3 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
>>>> index 3b7a3980ff50d6bf..312cd658bec0083b 100644
>>>> --- a/drivers/of/overlay.c
>>>> +++ b/drivers/of/overlay.c
>>>> @@ -630,11 +630,10 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
>>>> {
>>>> int i;
>>>>
>>>> - if (!ovcs->cset.entries.next)
>>>> - return;
>>>> - of_changeset_destroy(&ovcs->cset);
>>>> + if (ovcs->cset.entries.next)
>>>> + of_changeset_destroy(&ovcs->cset);
>>>>
>>>
>>> OK
>>>
>>>> - if (ovcs->id)
>>>> + if (ovcs->id > 0)
>>>
>>> Instead of this change, could you please make a change in init_overlay_changeset()?
>>>
>>> Current init_overlay_changeset():
>>>
>>> ovcs->id = idr_alloc(&ovcs_idr, ovcs, 1, 0, GFP_KERNEL);
>>> if (ovcs->id <= 0)
>>> return ovcs->id;
>>>
>>> My proposed version:
>>>
>>> ret = idr_alloc(&ovcs_idr, ovcs, 1, 0, GFP_KERNEL);
>>> if (ret <= 0)
>>> return ret;
>>> ovcs->id = ret;
>>
>> Sure.
>
> Actually we should use a temporary variable id here, just like for cnt
> and fragments, and store into ovcs->id if everything succeeds.
OK. That would make the flow in init_overlay_changeset() more consistent.
And of course the idr_remove() after err_free_idr: would use that temporary
variable id.
> Else both init_overlay_changeset() and free_overlay_changeset() will
> free the ID if something goes wrong. It seems IDR can handle that, but
> better safe than sorry.>
> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
>
> 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
>
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