linux-kernel - Re: [PATCH] Smack: check for SMACK xattr max size in smack_inode

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Date:	Tue, 14 Apr 2009 21:25:44 -0700
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Etienne Basset <etienne.basset@...ericable.fr>
CC:	LSM <linux-security-module@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH] Smack: check for SMACK xattr max size in  smack_inode_setxattr

Etienne Basset wrote:
> the following patch move the check for SMACK xattr size >= SMK_LABELLEN
> from  smack_inode_post_setxattr (which cannot return an error to the user)
> to smack_inode_setxattr (which can return an error).
>
> without patch a SMACK setxattr with size >= SMK_LABELLEN returns success although it doesn't 
>   

How about an early call to smk_import() to determine if the
label if legitimate, rather than checking the length? That
could save grief for other "invalid label" issues.

> Signed-off-by: Etienne Basset <etienne.basset@...ericable.fr>
> ---
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 9215149..da6954d 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -610,7 +610,8 @@ static int smack_inode_setxattr(struct dentry *dentry, const char *name,
>  		if (!capable(CAP_MAC_ADMIN))
>  			rc = -EPERM;
>  		/* a label cannot be void and cannot begin with '-' */
> -		if (size == 0 || (size > 0 && ((char *)value)[0] == '-'))
> +		if (size == 0 || size >= SMK_LABELLEN ||
> +		   (size > 0 && ((char *)value)[0] == '-'))
>  			rc = -EINVAL;
>  	} else
>  		rc = cap_inode_setxattr(dentry, name, value, size, flags);
> @@ -644,9 +645,6 @@ static void smack_inode_post_setxattr(struct dentry *dentry, const char *name,
>  	if (strcmp(name, XATTR_NAME_SMACK))
>  		return;
>  
> -	if (size >= SMK_LABELLEN)
> -		return;
> -
>  	isp = dentry->d_inode->i_security;
>  
>  	/*
>
> --
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>   

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