linux-kernel - Re: [PATCH 45/46] selinux: Use common error handling code in sidtab

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Date:   Tue, 17 Jan 2017 10:02:40 -0800
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     SF Markus Elfring <elfring@...rs.sourceforge.net>,
        linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov,
        Eric Paris <eparis@...isplace.org>,
        James Morris <james.l.morris@...cle.com>,
        Paul Moore <paul@...l-moore.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        William Roberts <william.c.roberts@...el.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 45/46] selinux: Use common error handling code in
 sidtab_insert()

On 1/15/2017 7:45 AM, SF Markus Elfring wrote:
> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Sun, 15 Jan 2017 13:45:45 +0100
>
> Add a jump target so that a bit of exception handling can be better reused
> at the end of this function.
>
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>  security/selinux/ss/sidtab.c | 18 ++++++++----------
>  1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/security/selinux/ss/sidtab.c b/security/selinux/ss/sidtab.c
> index f6915f257486..4130f882808c 100644
> --- a/security/selinux/ss/sidtab.c
> +++ b/security/selinux/ss/sidtab.c
> @@ -35,10 +35,8 @@ int sidtab_insert(struct sidtab *s, u32 sid, struct context *context)
>  	int hvalue, rc = 0;
>  	struct sidtab_node *prev, *cur, *newnode;
>  
> -	if (!s) {
> -		rc = -ENOMEM;
> -		goto out;
> -	}
> +	if (!s)
> +		goto failure_indication;
>  
>  	hvalue = SIDTAB_HASH(sid);
>  	prev = NULL;
> @@ -54,15 +52,12 @@ int sidtab_insert(struct sidtab *s, u32 sid, struct context *context)
>  	}
>  
>  	newnode = kmalloc(sizeof(*newnode), GFP_ATOMIC);
> -	if (!newnode) {
> -		rc = -ENOMEM;
> -		goto out;

Why not "return -ENOMEM;" ?

> -	}
> +	if (!newnode)
> +		goto failure_indication;
>  	newnode->sid = sid;
>  	if (context_cpy(&newnode->context, context)) {
>  		kfree(newnode);
> -		rc = -ENOMEM;
> -		goto out;
> +		goto failure_indication;

Again, "return -ENOMEM:"

>  	}
>  
>  	if (prev) {
> @@ -80,6 +75,9 @@ int sidtab_insert(struct sidtab *s, u32 sid, struct context *context)
>  		s->next_sid = sid + 1;
>  out:
>  	return rc;
> +failure_indication:
> +	rc = -ENOMEM;
> +	goto out;

Backward gotos are horrible. Don't do this.

>  }
>  
>  static struct context *sidtab_search_core(struct sidtab *s, u32 sid, int force)