linux-kernel - Re: [PATCH] of: overlay: fix null pointer dereferencing in find_dup_cset_node_entry() and find_dup_cset

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Date:   Fri, 9 Dec 2022 14:59:00 -0600
From:   Rob Herring <robh@...nel.org>
To:     ruanjinjie <ruanjinjie@...wei.com>
Cc:     frowand.list@...il.com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] of: overlay: fix null pointer dereferencing in
 find_dup_cset_node_entry() and find_dup_cset_prop()

On Tue, Dec 06, 2022 at 04:36:57PM +0800, ruanjinjie wrote:
> when kmalloc() fail to allocate memory in kasprintf(), fn_1 or fn_2 will
> be NULL, strcmp() will cause null pointer dereference.
> 
> Fixes: 2fe0e8769df9 ("of: overlay: check prevents multiple fragments touching same property")
> Signed-off-by: ruanjinjie <ruanjinjie@...wei.com>
> ---
>  drivers/of/overlay.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
> index bd8ff4df723d..49c066b51148 100644
> --- a/drivers/of/overlay.c
> +++ b/drivers/of/overlay.c
> @@ -545,6 +545,11 @@ static int find_dup_cset_node_entry(struct overlay_changeset *ovcs,
>  
>  		fn_1 = kasprintf(GFP_KERNEL, "%pOF", ce_1->np);
>  		fn_2 = kasprintf(GFP_KERNEL, "%pOF", ce_2->np);
> +		if (!fn_1 || !fn_2) {
> +			kfree(fn_1);
> +			kfree(fn_2);
> +			return -ENOMEM;
> +		}
>  		node_path_match = !strcmp(fn_1, fn_2);

We don't actually care what the return code is, so just change this to:

node_path_match = !fn_1 || !fn_2 || !strcmp(fn_1, fn_2);

>  		kfree(fn_1);
>  		kfree(fn_2);
> @@ -580,6 +585,11 @@ static int find_dup_cset_prop(struct overlay_changeset *ovcs,
>  
>  		fn_1 = kasprintf(GFP_KERNEL, "%pOF", ce_1->np);
>  		fn_2 = kasprintf(GFP_KERNEL, "%pOF", ce_2->np);
> +		if (!fn_1 || !fn_2) {
> +			kfree(fn_1);
> +			kfree(fn_2);
> +			return -ENOMEM;
> +		}
>  		node_path_match = !strcmp(fn_1, fn_2);
>  		kfree(fn_1);
>  		kfree(fn_2);
> -- 
> 2.25.1
> 
>