linux-kernel - Re: [PATCH] of: overlay: fix memory leak of ovcs on error exit path

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Message-ID: <CAL_JsqLQsEKr4K=rOa6qeA-uxpKQuTb1LvvMBHpiXenz8Jp6xg@mail.gmail.com>
Date:   Thu, 30 Nov 2017 09:26:29 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Frank Rowand <frowand.list@...il.com>
Cc:     Colin Ian King <colin.king@...onical.com>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        kernel-janitors@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] of: overlay: fix memory leak of ovcs on error exit path

On Thu, Nov 30, 2017 at 9:01 AM, Frank Rowand <frowand.list@...il.com> wrote:
> On 11/30/17 08:37, Frank Rowand wrote:
>> Hi Colin, Rob,
>>
>> On 11/30/17 07:18, Colin Ian King wrote:
>>> On 30/11/17 12:14, Frank Rowand wrote:
>>>> On 11/29/17 14:17, Colin King wrote:
>>>>> From: Colin Ian King <colin.king@...onical.com>
>>>>>
>>>>> Currently if the call to of_resolve_phandles fails then then ovcs
>>>>> is not kfree'd on the error exit path.  Rather than try and make
>>>>> the clean up exit path more convoluted, fix this by just kfree'ing
>>>>> ovcs at the point of error detection and exit via the same exit
>>>>> path.
>>>>>
>>>>> Detected by CoverityScan, CID#1462296 ("Resource Leak")
>>>>>
>>>>> Fixes: f948d6d8b792 ("of: overlay: avoid race condition between applying multiple overlays")
>>>>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>>>>> ---
>>>>>  drivers/of/overlay.c | 4 +++-
>>>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
>>>>> index 53bc9e3f0b98..6c8efe7d8cbb 100644
>>>>> --- a/drivers/of/overlay.c
>>>>> +++ b/drivers/of/overlay.c
>>>>> @@ -708,8 +708,10 @@ int of_overlay_apply(struct device_node *tree, int *ovcs_id)
>>>>>    of_overlay_mutex_lock();
>>>>>
>>>>>    ret = of_resolve_phandles(tree);
>>>>> -  if (ret)
>>>>> +  if (ret) {
>>>>> +          kfree(ovcs);
>>>>>            goto err_overlay_unlock;
>>>>> +  }
>>>>>
>>>>>    mutex_lock(&of_mutex);
>>>>>
>>>>>
>>>>
>>>> False coverity warning.  ovcs is freed in free_overlay_changeset().
>>>>
>>>
>>> The error exit path is via err_overlay_unlock:
>>>
>>> err_overlay_unlock:
>>>         of_overlay_mutex_unlock();
>>>
>>> out:
>>>         pr_debug("%s() err=%d\n", __func__, ret);
>>>
>>>         return ret;
>>>
>>> ..so there is no call to free_overlay_changeset there.
>>>
>>> Colin
>>>
>>
>> OK, I was looking at 4.15-rc1.  You must be looking at a later version where
>> "[PATCH 1/2] of: overlay: Fix cleanup order in of_overlay_apply()" has been
>> applied.  Thanks for providing the extra details about the exit path so I
>> could see that.
>>
>> Rob, I think that the fix for cleanup order was not the best way to fix that
>> problem.  A better method would have been to move "mutex_lock(&of_mutex);"
>> up 5 lines, to just before calling of_reserve_phandles().
>
> It is getting late (midnight my time), so I really should revisit this all
> tomorrow.  My last comment ("move ... up 5 lines") is probably wrong.
>
> I'll look at this after some sleep.

I'm dropping "of: overlay: Fix cleanup order in of_overlay_apply()",
so someone please fix this in the original patch.

Rob