linux-kernel - Re: [PATCH] SELinux: Create a common helper to determine an inode label

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Date:	Thu, 18 Jun 2015 12:34:15 -0400
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	David Howells <dhowells@...hat.com>
CC:	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-unionfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	SELinux <selinux@...ho.nsa.gov>, Paul Moore <paul@...l-moore.com>
Subject: Re: [PATCH] SELinux: Create a common helper to determine an inode
 label

On 06/18/2015 12:19 PM, David Howells wrote:
>     
> Create a common helper function to determine the label for a new inode.
> This is then used by:
> 
> 	- may_create()
> 	- selinux_dentry_init_security()
> 	- selinux_inode_init_security()
> 
> This will change the behaviour of the functions slightly, bringing them all
> into line.
> 
> Suggested-by: Stephen Smalley <sds@...ho.nsa.gov>
> Signed-off-by: David Howells <dhowells@...hat.com>
> ---
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index ffa5a642629a..902113d71acd 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -1684,6 +1684,32 @@ out:
>  	return rc;
>  }
>  
> +/*
> + * Determine the label for an inode that might be unioned.
> + */
> +static int selinux_determine_inode_label(const struct inode *dir,
> +					 const struct qstr *name,
> +					 u16 tclass,
> +					 u32 *_new_isid)
> +{
> +	const struct superblock_security_struct *sbsec = dir->i_sb->s_security;
> +	const struct inode_security_struct *dsec = dir->i_security;
> +	const struct task_security_struct *tsec = current_security();
> +
> +	if ((sbsec->flags & SE_SBINITIALIZED) &&
> +	    (sbsec->behavior == SECURITY_FS_USE_MNTPOINT)) {
> +		*_new_isid = sbsec->mntpoint_sid;
> +	} else if ((sbsec->flags & SBLABEL_MNT) &&
> +		   tsec->create_sid) {
> +		*_new_isid = tsec->create_sid;
> +	} else {
> +		return security_transition_sid(tsec->sid, dsec->sid, tclass,
> +					       name, _new_isid);
> +	}
> +
> +	return 0;
> +}
> +
>  /* Check whether a task can create a file. */
>  static int may_create(struct inode *dir,
>  		      struct dentry *dentry,
> @@ -1700,7 +1726,6 @@ static int may_create(struct inode *dir,
>  	sbsec = dir->i_sb->s_security;
>  
>  	sid = tsec->sid;
> -	newsid = tsec->create_sid;
>  
>  	ad.type = LSM_AUDIT_DATA_DENTRY;
>  	ad.u.dentry = dentry;
> @@ -1711,12 +1736,10 @@ static int may_create(struct inode *dir,
>  	if (rc)
>  		return rc;
>  
> -	if (!newsid || !(sbsec->flags & SBLABEL_MNT)) {
> -		rc = security_transition_sid(sid, dsec->sid, tclass,
> -					     &dentry->d_name, &newsid);
> -		if (rc)
> -			return rc;
> -	}
> +	rc = selinux_determine_inode_label(dir, &dentry->d_name, tclass,
> +					   &newsid);
> +	if (rc)
> +		return rc;
>  
>  	rc = avc_has_perm(sid, newsid, tclass, FILE__CREATE, &ad);
>  	if (rc)
> @@ -2723,32 +2746,14 @@ static int selinux_dentry_init_security(struct dentry *dentry, int mode,
>  					struct qstr *name, void **ctx,
>  					u32 *ctxlen)
>  {
> -	const struct cred *cred = current_cred();
> -	struct task_security_struct *tsec;
> -	struct inode_security_struct *dsec;
> -	struct superblock_security_struct *sbsec;
> -	struct inode *dir = d_backing_inode(dentry->d_parent);
>  	u32 newsid;
>  	int rc;
>  
> -	tsec = cred->security;
> -	dsec = dir->i_security;
> -	sbsec = dir->i_sb->s_security;
> -
> -	if (tsec->create_sid && sbsec->behavior != SECURITY_FS_USE_MNTPOINT) {
> -		newsid = tsec->create_sid;
> -	} else {
> -		rc = security_transition_sid(tsec->sid, dsec->sid,
> -					     inode_mode_to_security_class(mode),
> -					     name,
> -					     &newsid);
> -		if (rc) {
> -			printk(KERN_WARNING
> -				"%s: security_transition_sid failed, rc=%d\n",
> -			       __func__, -rc);
> -			return rc;
> -		}
> -	}
> +	rc = selinux_determine_inode_label(d_inode(dentry), name,

Hmmm...previously we were using d_backing_inode(dentry->d_parent) here.

> +					   inode_mode_to_security_class(mode),
> +					   &newsid);
> +	if (rc)
> +		return rc;
>  
>  	return security_sid_to_context(newsid, (char **)ctx, ctxlen);
>  }
> @@ -2771,22 +2776,12 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
>  	sid = tsec->sid;
>  	newsid = tsec->create_sid;
>  
> -	if ((sbsec->flags & SE_SBINITIALIZED) &&
> -	    (sbsec->behavior == SECURITY_FS_USE_MNTPOINT))
> -		newsid = sbsec->mntpoint_sid;
> -	else if (!newsid || !(sbsec->flags & SBLABEL_MNT)) {
> -		rc = security_transition_sid(sid, dsec->sid,
> -					     inode_mode_to_security_class(inode->i_mode),
> -					     qstr, &newsid);
> -		if (rc) {
> -			printk(KERN_WARNING "%s:  "
> -			       "security_transition_sid failed, rc=%d (dev=%s "
> -			       "ino=%ld)\n",
> -			       __func__,
> -			       -rc, inode->i_sb->s_id, inode->i_ino);
> -			return rc;
> -		}
> -	}
> +	rc = selinux_determine_inode_label(
> +		dir, qstr,
> +		inode_mode_to_security_class(inode->i_mode),
> +		&newsid);
> +	if (rc)
> +		return rc;
>  
>  	/* Possibly defer initialization to selinux_complete_init. */
>  	if (sbsec->flags & SE_SBINITIALIZED) {
> 
> 

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