Hi Frank,
On Tue, Dec 5, 2017 at 3:07 AM, Frank Rowand <frowand.l...@gmail.com> 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.k...@canonical.com>
>> Fixes: f948d6d8b792bb90 ("of: overlay: avoid race condition between applying
>> multiple overlays")
>> Signed-off-by: Geert Uytterhoeven <geert+rene...@glider.be>
>> ---
>> 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.
>> idr_remove(&ovcs_idr, ovcs->id);
>>
>> for (i = 0; i < ovcs->count; i++) {
>>
>
> Also, the previous version of the patch, and the discussion around the
> resulting
> bug make me think that I should not have moved 'kfree(ovcs)' into
> free_overlay_changeset(), because that kfree is then not very visible in the
> error path of of_overlay_apply(). Could you remove 'kfree(ovcs)' from
> free_overlay_changeset(), and instead call it immediately after each call
> to free_overlay_changeset()?
Actually I like that free_overlay_changeset() takes care of the deallocation,
especially in light of the kojectification op top from bbb-overlays, which
means you cannot just call kfree(ovcs) anymore (I know this won't go upstream
anytime soon, but I need overlay configfs for my development and testing).
Perhaps the allocation of ovcs should be moved into free_overlay_changeset(),
and the latter being renamed to alloc_overlay_changeset()?
That way allocation and freeing become symmetrical.
It would move the allocation under the mutexes, though.
What do you think?
Thanks!
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-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
