linux-kernel - Re: [PATCH] drivers:of:property.c: fix a potential double put (release) bug

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Date:   Wed, 18 Aug 2021 09:07:31 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Wentao_Liang <Wentao_Liang_g@....com>,
        Saravana Kannan <saravanak@...gle.com>
Cc:     Frank Rowand <frowand.list@...il.com>, devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers:of:property.c: fix a potential double put
 (release) bug

+Saravana

On Wed, Aug 18, 2021 at 8:26 AM Wentao_Liang <Wentao_Liang_g@....com> wrote:
>
> In line 1423 (#1), of_link_to_phandle() is called. In the function
> (line 1140, #2), "of_node_put(sup_np);" drops the reference to phandle
> and may cause phandle to be released. However, after the function
> returns, the phandle is subsequently dropped again (line 1424, #3) by
> the same put function. Double putting the phandle can lead to an
> incorrect reference count.
>
> We believe that the first put of the phandle is unnecessary (#3). We
> can fix the above bug by removing the redundant "of_node_put()" in line
> 1423.
>
> 1401 static int of_link_property(struct device_node *con_np,
>                                 const char *prop_name)
> 1402 {
> ...
> 1409     while (!matched && s->parse_prop) {
> ...
> 1414
> 1415         while ((phandle = s->parse_prop(con_np, prop_name, i))) {
> ...
>                  //#1 phandle is dropped in this function
> 1423             of_link_to_phandle(con_dev_np, phandle);
>
> 1424             //#3 the second drop to phandle
>                  of_node_put(phandle);
>
> 1425             of_node_put(con_dev_np);
> 1426         }
> ...
> 1428     }
> 1429     return 0;
> 1430 }
>
> 1095 static int of_link_to_phandle(struct device_node *con_np,
> 1096                   struct device_node *sup_np)
> 1097 {
> 1098     struct device *sup_dev;
> 1099     struct device_node *tmp_np = sup_np;
> ...
> 1140     of_node_put(sup_np);  //#2 the first drop to phandle
>                                //   (unnecessary)
> 1141
> 1142     return 0;
> 1143 }
>
> Signed-off-by: Wentao_Liang <Wentao_Liang_g@....com>
> ---
>  drivers/of/property.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/drivers/of/property.c b/drivers/of/property.c
> index 6c028632f425..408fdde1a20c 100644
> --- a/drivers/of/property.c
> +++ b/drivers/of/property.c
> @@ -1137,7 +1137,6 @@ static int of_link_to_phandle(struct device_node *con_np,
>         put_device(sup_dev);
>
>         fwnode_link_add(of_fwnode_handle(con_np), of_fwnode_handle(sup_np));
> -       of_node_put(sup_np);
>
>         return 0;
>  }
> --
> 2.25.1
>