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

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Message-ID: <75d7d1c8-8a19-1a4c-0796-7cf69fdebe6d@gmail.com>
Date:   Thu, 30 Nov 2017 08:37:09 -0500
From:   Frank Rowand <frowand.list@...il.com>
To:     Colin Ian King <colin.king@...onical.com>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] of: overlay: fix memory leak of ovcs on error exit path

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().  The problem
found by coverity was caused by the "Fix cleanup order" patch.

I can create that alternate fix if you would like, but I am traveling
right now and don't want to submit a patch without boot testing, so
there will be a slight delay.

-Frank