linux-kernel - Re: [PATCH v2] clk: zynq: Prevent null pointer dereference caused by kmalloc failure

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Message-ID: <2b274111-e65a-4b99-8f07-220324f1e214@amd.com>
Date: Thu, 29 Feb 2024 13:45:54 +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,
 sboyd@...nel.org, mturquette@...libre.com
Subject: Re: [PATCH v2] clk: zynq: Prevent null pointer dereference caused by
 kmalloc failure



On 2/29/24 13:22, 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 adds 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 v2:
>    - Use stack variable to replace kmalloc().
> 
>   drivers/clk/zynq/clkc.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/zynq/clkc.c b/drivers/clk/zynq/clkc.c
> index 7bdeaff2bfd..e4c4c9adf79 100644
> --- a/drivers/clk/zynq/clkc.c
> +++ b/drivers/clk/zynq/clkc.c
> @@ -427,7 +427,7 @@ static void __init zynq_clk_setup(struct device_node *np)
>   			SLCR_GEM1_CLK_CTRL, 0, 0, &gem1clk_lock);
>   
>   	tmp = strlen("mio_clk_00x");
> -	clk_name = kmalloc(tmp, GFP_KERNEL);
> +	char clk_name[tmp];

I know that Stephen asked for it but variable with variable length in the middle 
of code doesn't look good or useful.
I would allocate rather bigger array on stack with size bigger than max length 
which will use it.

Thanks,
Michal