linux-kernel - Re: [PATCH] lkdtm: Add checks after calling kmalloc and vmalloc

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Date:   Wed, 31 Aug 2022 09:00:20 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Jiasheng Jiang <jiasheng@...as.ac.cn>
Cc:     keescook@...omium.org, arnd@...db.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lkdtm: Add checks after calling kmalloc and vmalloc

On Wed, Aug 31, 2022 at 02:53:55PM +0800, Jiasheng Jiang wrote:
> As the potential failure of the memory allocation,
> it should be better to check the return value after
> calling kmalloc and vmalloc and skip the execute_location
> if fails.
> 
> Fixes: cc33c537c12f ("lkdtm: add "EXEC_*" triggers")
> Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>
> ---
>  drivers/misc/lkdtm/perms.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
> index b93404d65650..9ba927d74973 100644
> --- a/drivers/misc/lkdtm/perms.c
> +++ b/drivers/misc/lkdtm/perms.c
> @@ -180,14 +180,16 @@ static void lkdtm_EXEC_STACK(void)
>  static void lkdtm_EXEC_KMALLOC(void)
>  {
>  	u32 *kmalloc_area = kmalloc(EXEC_SIZE, GFP_KERNEL);
> -	execute_location(kmalloc_area, CODE_WRITE);
> +	if (kmalloc_area)

How will this ever fail?  Have you seen that happen?

> +		execute_location(kmalloc_area, CODE_WRITE);
>  	kfree(kmalloc_area);
>  }
>  
>  static void lkdtm_EXEC_VMALLOC(void)
>  {
>  	u32 *vmalloc_area = vmalloc(EXEC_SIZE);
> -	execute_location(vmalloc_area, CODE_WRITE);
> +	if (vmalloc_area)

Same here, if the system really can not allocate 64 bytes, much worse
things will have happened already.

thanks,

greg k-h