linux-kernel - Re: [PATCH 1/2] of: overlay: fix properties memory leak

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Date:   Thu, 21 Nov 2019 10:55:26 -0600
From:   Frank Rowand <frowand.list@...il.com>
To:     Vincent Whitchurch <vincent.whitchurch@...s.com>,
        pantelis.antoniou@...sulko.com, robh+dt@...nel.org
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vincent Whitchurch <rabinv@...s.com>
Subject: Re: [PATCH 1/2] of: overlay: fix properties memory leak

Hi Vincent,

On 11/18/19 7:28 AM, Vincent Whitchurch wrote:
> No changeset entries are created for #address-cells and #size-cells
> properties, but the duplicated properies are never freed.  This results
> in a memory leak which is detected by kmemleak:
> 
>  unreferenced object 0x85887180 (size 64):
>    backtrace:
>      kmem_cache_alloc_trace+0x1fb/0x1fc
>      __of_prop_dup+0x25/0x7c
>      add_changeset_property+0x17f/0x370
>      build_changeset_next_level+0x29/0x20c
>      of_overlay_fdt_apply+0x32b/0x6b4
>      ...
> 
> Fixes: 6f75118800acf77f8 ("of: overlay: validate overlay properties #address-cells and #size-cells")
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@...s.com>
> ---
>  drivers/of/overlay.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
> index c423e94baf0f..5f8869e2a8b3 100644
> --- a/drivers/of/overlay.c
> +++ b/drivers/of/overlay.c
> @@ -360,7 +360,7 @@ static int add_changeset_property(struct overlay_changeset *ovcs,
>  		pr_err("WARNING: memory leak will occur if overlay removed, property: %pOF/%s\n",
>  		       target->np, new_prop->name);
>  
> -	if (ret) {
> +	if (ret || !check_for_non_overlay_node) {
>  		kfree(new_prop->name);
>  		kfree(new_prop->value);
>  		kfree(new_prop);
> 

Thanks for finding and proposing a fix for the memory leak.

The proposed patch conveniently uses check_for_non_overlay_node
which leads to a nice small patch.  But ends up adding an
additional hidden meaning to the variable, resulting in more
fragile code.

I will propose a different solution and ask you to test it
to make sure it also solves the memory leak.

-Frank