linux-kernel - Re: [PATCH] lkdtm: use the return value of strim()

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Date:   Thu, 17 Aug 2023 09:55:22 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "GONG, Ruiqi" <gongruiqi@...weicloud.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, gongruiqi1@...wei.com
Subject: Re: [PATCH] lkdtm: use the return value of strim()

On Thu, Aug 17, 2023 at 10:21:17PM +0800, GONG, Ruiqi wrote:
> From: "GONG, Ruiqi" <gongruiqi1@...wei.com>
> 
> Make use of the return value of strim() to achieve left-trim as well as
> right-trim, which prevents the following unusual fail case:
> 
>  # echo " EXCEPTION" > /sys/kernel/debug/provoke-crash/DIRECT
>  sh: write error: Invalid argument
> 
> Link: https://github.com/KSPP/linux/issues/337
> Signed-off-by: GONG, Ruiqi <gongruiqi1@...wei.com>
> ---
>  drivers/misc/lkdtm/core.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c
> index 0772e4a4757e..812c96461ab2 100644
> --- a/drivers/misc/lkdtm/core.c
> +++ b/drivers/misc/lkdtm/core.c
> @@ -242,7 +242,7 @@ static ssize_t lkdtm_debugfs_entry(struct file *f,
>  	}
>  	/* NULL-terminate and remove enter */
>  	buf[count] = '\0';
> -	strim(buf);
> +	buf = strim(buf);
>  
>  	crashtype = find_crashtype(buf);
>  	free_page((unsigned long)buf);

Will free_page() still work in this case, though? The address won't
match the allocation any more...

-Kees

> @@ -318,7 +318,7 @@ static ssize_t direct_entry(struct file *f, const char __user *user_buf,
>  	}
>  	/* NULL-terminate and remove enter */
>  	buf[count] = '\0';
> -	strim(buf);
> +	buf = strim(buf);
>  
>  	crashtype = find_crashtype(buf);
>  	free_page((unsigned long) buf);
> -- 
> 2.25.1
> 

-- 
Kees Cook