Re: [PATCH] SELinux: Create a common helper to determine an inode label [ver #2]

[Stephen Smalley]

On 06/18/2015 01:08 PM, Stephen Smalley wrote:
> On 06/18/2015 12:41 PM, David Howells wrote:
>> SELinux: Create a common helper to determine an inode label
>>
>> 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@xxxxxxxxxxxxx>
>> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
>> ---
>> 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,
> 
> We want d_inode(dentry->d_parent) here.

Not sure why the caller didn't just pass in the dir inode in the first
place.

> 
>> +					   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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