linux-kernel - Re: [PATCH 1/3] ima_fs: One check less in ima_write

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Message-Id: <1485520737.2596.88.camel@linux.vnet.ibm.com>
Date:   Fri, 27 Jan 2017 07:38:57 -0500
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     SF Markus Elfring <elfring@...rs.sourceforge.net>
Cc:     linux-ima-devel@...ts.sourceforge.net,
        linux-ima-user@...ts.sourceforge.net,
        linux-security-module@...r.kernel.org,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        James Morris <james.l.morris@...cle.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 1/3] ima_fs: One check less in ima_write_policy() after
 error detection

On Wed, 2017-01-25 at 10:31 +0100, SF Markus Elfring wrote:
> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Tue, 24 Jan 2017 20:30:55 +0100
> 
> Move the jump label directly before the desired assignment for the
> variable "valid_policy" at the end so that the variable "result" will not
> be checked once more after it was determined that a received input
> parameter was not zero or a memory allocation failed.
> Use the identifier "reset_validity" instead of the label "out".
> 
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>  security/integrity/ima/ima_fs.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> index ca303e5d2b94..c1c8d34d111d 100644
> --- a/security/integrity/ima/ima_fs.c
> +++ b/security/integrity/ima/ima_fs.c
> @@ -321,12 +321,12 @@ static ssize_t ima_write_policy(struct file *file, const char __user *buf,
>  	/* No partial writes. */
>  	result = -EINVAL;
>  	if (*ppos != 0)
> -		goto out;
> +		goto reset_validity;
> 
>  	result = -ENOMEM;
>  	data = kmalloc(datalen + 1, GFP_KERNEL);
>  	if (!data)
> -		goto out;
> +		goto reset_validity;
> 
>  	*(data + datalen) = '\0';
> 
> @@ -353,8 +353,8 @@ static ssize_t ima_write_policy(struct file *file, const char __user *buf,
>  	mutex_unlock(&ima_write_mutex);
>  out_free:
>  	kfree(data);
> -out:
>  	if (result < 0)
> +reset_validity:

Really?!   Do you really think this makes the code more readable?   A
more common, readable approach is to have two exit points - a normal
exit and an error exit.   Let's leave it to the compiler to do the
optimization.

Mimi

>  		valid_policy = 0;
> 
>  	return result;