linux-kernel - Re: [PATCH] clk: imx: Fix a NULL pointer dereference in imx_register_uart

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Date:   Fri, 28 Jan 2022 11:16:20 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Zhou Qingyang <zhou1615@....edu>
Cc:     kjlu@....edu, Abel Vesa <abel.vesa@....com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Adam Ford <aford173@...il.com>, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: imx: Fix a NULL pointer dereference in
 imx_register_uart_clocks()

On Tue, Jan 25, 2022 at 12:52:06AM +0800, Zhou Qingyang wrote:
> In imx_register_uart_clocks(), the global variable imx_uart_clocks is
> assigned by kcalloc() and there is a dereference of in the next for loop,
> which could introduce a NULL pointer dereference on failure of kcalloc().
> 
> Fix this by adding a NULL check of imx_uart_clocks.
> 
> This bug was found by a static analyzer.
> 
> Builds with 'make allyesconfig' show no new warnings,
> and our static analyzer no longer warns about this code.
> 
> Fixes: 379c9a24cc23 ("clk: imx: Fix reparenting of UARTs not associated with stdout")
> Signed-off-by: Zhou Qingyang <zhou1615@....edu>
> ---
> The analysis employs differential checking to identify inconsistent 
> security operations (e.g., checks or kfrees) between two code paths 
> and confirms that the inconsistent operations are not recovered in the
> current function or the callers, so they constitute bugs. 
> 
> Note that, as a bug found by static analysis, it can be a false
> positive or hard to trigger. Multiple researchers have cross-reviewed
> the bug.
> 
>  drivers/clk/imx/clk.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/clk/imx/clk.c b/drivers/clk/imx/clk.c
> index 7cc669934253..99249ab361d2 100644
> --- a/drivers/clk/imx/clk.c
> +++ b/drivers/clk/imx/clk.c
> @@ -173,6 +173,8 @@ void imx_register_uart_clocks(unsigned int clk_count)
>  		int i;
>  
>  		imx_uart_clocks = kcalloc(clk_count, sizeof(struct clk *), GFP_KERNEL);
> +		if (!imx_uart_clocks)
> +			return;
>  
>  		if (!of_stdout)
>  			return;
> -- 
> 2.25.1
> 

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