linux-kernel - Re: [patch] smack: opt_dentry is never null in in smack_d

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Date:	Tue, 01 Jun 2010 17:26:06 -0700
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Dan Carpenter <error27@...il.com>,
	James Morris <jmorris@...ei.org>,
	Casey Schaufler <casey@...aufler-ca.com>,
	"David P. Quigley" <dpquigl@...ho.nsa.gov>,
	David Howells <dhowells@...hat.com>,
	Serge Hallyn <serue@...ibm.com>,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [patch] smack: opt_dentry is never null in in smack_d_instantiate()

Dan Carpenter wrote:
> This patch removes some unneeded code for if opt_dentry is null because
> that can never happen.
>
> The function dereferences "opt_dentry" earlier when it checks 
> "if (opt_dentry->d_parent == opt_dentry) {".  That code was added in
> 2008.
>
> This function called from security_d_instantiate().  I checked all the 
> places which call security_d_instantiate() and dentry is always non-null.
> I also checked the selinux version of this hook and there is a comment
> which says that dentry should be non-null if called from 
> d_instantiate().
>
> Signed-off-by: Dan Carpenter <error27@...il.com>
>   

Acked-by: Casey Schaufler <casey@...aufler-ca.com>

I have tested the change and not had any issues. I recall struggling
with this particular bit of code, but that was long enough ago that
the circumstances evade my memory. Thank you.

> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 0f2fc48..07abc9c 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -2191,7 +2191,7 @@ static void smack_ipc_getsecid(struct kern_ipc_perm *ipp, u32 *secid)
>  
>  /**
>   * smack_d_instantiate - Make sure the blob is correct on an inode
> - * @opt_dentry: unused
> + * @opt_dentry: dentry where inode will be attached
>   * @inode: the object
>   *
>   * Set the inode's security blob if it hasn't been done already.
> @@ -2310,20 +2310,10 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
>  		/*
>  		 * Get the dentry for xattr.
>  		 */
> -		if (opt_dentry == NULL) {
> -			dp = d_find_alias(inode);
> -			if (dp == NULL)
> -				break;
> -		} else {
> -			dp = dget(opt_dentry);
> -			if (dp == NULL)
> -				break;
> -		}
> -
> +		dp = dget(opt_dentry);
>  		fetched = smk_fetch(inode, dp);
>  		if (fetched != NULL)
>  			final = fetched;
> -
>  		dput(dp);
>  		break;
>  	}
>
>
>   

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