linux-kernel - Re: [PATCH v3] clk: zynq: Prevent null pointer dereference caused by kmalloc failure

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Message-ID: <d9b6d49e-9485-4733-a2d6-615bcc8f6ef3@amd.com>
Date: Fri, 1 Mar 2024 08:05:17 +0100
From: Michal Simek <michal.simek@....com>
To: Duoming Zhou <duoming@....edu.cn>, linux-kernel@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
 mturquette@...libre.com, sboyd@...nel.org
Subject: Re: [PATCH v3] clk: zynq: Prevent null pointer dereference caused by
 kmalloc failure



On 3/1/24 08:03, Duoming Zhou wrote:
> The kmalloc() in zynq_clk_setup() will return null if the
> physical memory has run out. As a result, if we use snprintf()
> to write data to the null address, the null pointer dereference
> bug will happen.
> 
> This patch uses a stack variable to replace the kmalloc().
> 
> Fixes: 0ee52b157b8e ("clk: zynq: Add clock controller driver")
> Signed-off-by: Duoming Zhou <duoming@....edu.cn>
> ---
> Changes in v3:
>    - Put stack variable in the head of the function and remove variable tmp.
> 
>   drivers/clk/zynq/clkc.c | 7 ++-----
>   1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/clk/zynq/clkc.c b/drivers/clk/zynq/clkc.c
> index 7bdeaff2bfd..45479653c3b 100644
> --- a/drivers/clk/zynq/clkc.c
> +++ b/drivers/clk/zynq/clkc.c
> @@ -215,7 +215,7 @@ static void __init zynq_clk_setup(struct device_node *np)
>   	int i;
>   	u32 tmp;
>   	int ret;
> -	char *clk_name;
> +	char clk_name[16];
>   	unsigned int fclk_enable = 0;
>   	const char *clk_output_name[clk_max];
>   	const char *cpu_parents[4];
> @@ -426,12 +426,10 @@ static void __init zynq_clk_setup(struct device_node *np)
>   			"gem1_emio_mux", CLK_SET_RATE_PARENT,
>   			SLCR_GEM1_CLK_CTRL, 0, 0, &gem1clk_lock);
>   
> -	tmp = strlen("mio_clk_00x");
> -	clk_name = kmalloc(tmp, GFP_KERNEL);
>   	for (i = 0; i < NUM_MIO_PINS; i++) {
>   		int idx;
>   
> -		snprintf(clk_name, tmp, "mio_clk_%2.2d", i);
> +		snprintf(clk_name, 16, "mio_clk_%2.2d", i);

I would prefer to use macro/define if that values has to match and have connection.

Thanks,
Michal