Re: [PATCH] SELinux: Create a common helper to determine an inode label [ver #3]

[Paul Moore <paul@paul-moore.com>]

On Thursday, June 18, 2015 07:25:05 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@tycho.nsa.gov>
> Signed-off-by: David Howells <dhowells@redhat.com>

This patch looks fine to me and I think there is an advantage to merging this 
regardless of what happens with the "unioning" work so I'm inclined to queue 
this up now unless you would prefer to resubmit with the union patches?

> ---
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index ffa5a642629a..ec30e599fb46 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->d_parent), name,
> +					   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) {

-- 
paul moore
www.paul-moore.com