Re: [PATCH] ep93xx: clock: Fix UAF in ep93xx_clk_register_gate()

[Nick Desaulniers]

On Thu, Jan 20, 2022 at 02:37:38PM +0100, Alexander Sverdlin wrote:
> arch/arm/mach-ep93xx/clock.c:151:2: note: Taking true branch
> if (IS_ERR(clk))
> ^
> arch/arm/mach-ep93xx/clock.c:152:3: note: Memory is released
> kfree(psc);
> ^~~~~~~~~~
> arch/arm/mach-ep93xx/clock.c:154:2: note: Use of memory after it is freed
> return &psc->hw;
> ^ ~~~~~~~~
> 
> Link: https://lists.01.org/hyperkitty/list/kbuild-all@xxxxxxxxxxxx/thread/B5YCO2NJEXINCYE26Y255LCVMO55BGWW/
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Fixes: 9645ccc7bd7a ("ep93xx: clock: convert in-place to COMMON_CLK")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxx>
> ---
>  arch/arm/mach-ep93xx/clock.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mach-ep93xx/clock.c b/arch/arm/mach-ep93xx/clock.c
> index cc75087134d3..4aee14f18123 100644
> --- a/arch/arm/mach-ep93xx/clock.c
> +++ b/arch/arm/mach-ep93xx/clock.c
> @@ -148,8 +148,10 @@ static struct clk_hw *ep93xx_clk_register_gate(const char *name,
>  	psc->lock = &clk_lock;
>  
>  	clk = clk_register(NULL, &psc->hw);
> -	if (IS_ERR(clk))
> +	if (IS_ERR(clk)) {
>  		kfree(psc);
> +		return (void *)clk;

Prefer ERR_CAST to the raw cast. I think that's nicer when we're already
using the IS_ERR macros.

> +	}
>  
>  	return &psc->hw;
>  }
> -- 
> 2.34.1
>