linux-kernel - Re: [PATCH] Kernel: Improvement in code readability when memdup_user

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Date:   Fri, 11 Nov 2016 10:55:57 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Sachin Shukla <sachin.s5@...sung.com>
Cc:     Kees Cook <keescook@...omium.org>, Serge Hallyn <serge@...lyn.com>,
        Andrey Vagin <avagin@...nvz.org>, linux-kernel@...r.kernel.org,
        sachiniiitm@...il.com, ravikant.s2@...sung.com,
        p.shailesh@...sung.com, ashish.kalra@...sung.com,
        vidushi.koul@...sung.com
Subject: Re: [PATCH] Kernel: Improvement in code readability when memdup_user_nul() fails.

Sachin Shukla <sachin.s5@...sung.com> writes:

> From: "Sachin Shukla" <sachin.s5@...sung.com>
>
> There is no need to call kfree() if memdup_user_nul() fails, as no memory
> was allocated and the error in the error-valued pointer should be
> returned.

Nacked-by: "Eric W. Biederman" <ebiederm@...ssion.com>

This is stupid, unnecesary gratituous change that makes the maintenance
of the code worse.


>
> Signed-off-by: Sachin Shukla <sachin.s5@...sung.com>
> ---
>  kernel/user_namespace.c |   25 ++++++++++++++-----------
>  1 file changed, 14 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 86b7854..a0ffbf0 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -672,28 +672,31 @@ static ssize_t map_write(struct file *file, const char __user *buf,
>  	 */
>  	mutex_lock(&userns_state_mutex);
>  
> -	ret = -EPERM;
>  	/* Only allow one successful write to the map */
> -	if (map->nr_extents != 0)
> -		goto out;
> +	if (map->nr_extents != 0) {
> +		mutex_unlock(&userns_state_mutex);
> +		return -EPERM;
> +	}
>  
>  	/*
>  	 * Adjusting namespace settings requires capabilities on the target.
>  	 */
> -	if (cap_valid(cap_setid) && !file_ns_capable(file, ns, CAP_SYS_ADMIN))
> -		goto out;
> +	if (cap_valid(cap_setid) && !file_ns_capable(file, ns, CAP_SYS_ADMIN)) {
> +		mutex_unlock(&userns_state_mutex);
> +		return -EPERM;
> +	}
>  
>  	/* Only allow < page size writes at the beginning of the file */
> -	ret = -EINVAL;
> -	if ((*ppos != 0) || (count >= PAGE_SIZE))
> -		goto out;
> +	if ((*ppos != 0) || (count >= PAGE_SIZE)) {
> +		mutex_unlock(&userns_state_mutex);
> +		return -EINVAL;
> +	}
>  
>  	/* Slurp in the user data */
>  	kbuf = memdup_user_nul(buf, count);
>  	if (IS_ERR(kbuf)) {
> -		ret = PTR_ERR(kbuf);
> -		kbuf = NULL;
> -		goto out;
> +		mutex_unlock(&userns_state_mutex);
> +		return PTR_ERR(kbuf);
>  	}
>  
>  	/* Parse the user data */