selinux: delay inode label lookup as long as possible

Since looking up an inode's label can result in revalidation, delay
the lookup as long as possible to limit the performance impact.
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/hooks.c

@@ -1790,7 +1790,6 @@ static int selinux_determine_inode_label(struct inode *dir,
 					 u32 *_new_isid)
 {
 	const struct superblock_security_struct *sbsec = dir->i_sb->s_security;
-	const struct inode_security_struct *dsec = inode_security(dir);
 	const struct task_security_struct *tsec = current_security();
 
 	if ((sbsec->flags & SE_SBINITIALIZED) &&
@@ -1800,6 +1799,7 @@ static int selinux_determine_inode_label(struct inode *dir,
 		   tsec->create_sid) {
 		*_new_isid = tsec->create_sid;
 	} else {
+		const struct inode_security_struct *dsec = inode_security(dir);
 		return security_transition_sid(tsec->sid, dsec->sid, tclass,
 					       name, _new_isid);
 	}
@@ -2084,7 +2084,7 @@ static int selinux_binder_transfer_file(struct task_struct *from,
 	u32 sid = task_sid(to);
 	struct file_security_struct *fsec = file->f_security;
 	struct dentry *dentry = file->f_path.dentry;
-	struct inode_security_struct *isec = backing_inode_security(dentry);
+	struct inode_security_struct *isec;
 	struct common_audit_data ad;
 	int rc;
 
@@ -2103,6 +2103,7 @@ static int selinux_binder_transfer_file(struct task_struct *from,
 	if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
 		return 0;
 
+	isec = backing_inode_security(dentry);
 	return avc_has_perm(sid, isec->sid, isec->sclass, file_to_av(file),
 			    &ad);
 }
@@ -3057,7 +3058,7 @@ static int selinux_inode_setxattr(struct dentry *dentry, const char *name,
 				  const void *value, size_t size, int flags)
 {
 	struct inode *inode = d_backing_inode(dentry);
-	struct inode_security_struct *isec = backing_inode_security(dentry);
+	struct inode_security_struct *isec;
 	struct superblock_security_struct *sbsec;
 	struct common_audit_data ad;
 	u32 newsid, sid = current_sid();
@@ -3076,6 +3077,7 @@ static int selinux_inode_setxattr(struct dentry *dentry, const char *name,
 	ad.type = LSM_AUDIT_DATA_DENTRY;
 	ad.u.dentry = dentry;
 
+	isec = backing_inode_security(dentry);
 	rc = avc_has_perm(sid, isec->sid, isec->sclass,
 			  FILE__RELABELFROM, &ad);
 	if (rc)
@@ -3134,7 +3136,7 @@ static void selinux_inode_post_setxattr(struct dentry *dentry, const char *name,
 					int flags)
 {
 	struct inode *inode = d_backing_inode(dentry);
-	struct inode_security_struct *isec = backing_inode_security(dentry);
+	struct inode_security_struct *isec;
 	u32 newsid;
 	int rc;
 
@@ -3151,6 +3153,7 @@ static void selinux_inode_post_setxattr(struct dentry *dentry, const char *name,
 		return;
 	}
 
+	isec = backing_inode_security(dentry);
 	isec->sclass = inode_mode_to_security_class(inode->i_mode);
 	isec->sid = newsid;
 	isec->initialized = LABEL_INITIALIZED;
@@ -3192,7 +3195,7 @@ static int selinux_inode_getsecurity(struct inode *inode, const char *name, void
 	u32 size;
 	int error;
 	char *context = NULL;
-	struct inode_security_struct *isec = inode_security(inode);
+	struct inode_security_struct *isec;
 
 	if (strcmp(name, XATTR_SELINUX_SUFFIX))
 		return -EOPNOTSUPP;
@@ -3211,6 +3214,7 @@ static int selinux_inode_getsecurity(struct inode *inode, const char *name, void
 	if (!error)
 		error = cred_has_capability(current_cred(), CAP_MAC_ADMIN,
 					    SECURITY_CAP_NOAUDIT);
+	isec = inode_security(inode);
 	if (!error)
 		error = security_sid_to_context_force(isec->sid, &context,
 						      &size);
@@ -3320,7 +3324,7 @@ static int ioctl_has_perm(const struct cred *cred, struct file *file,
 	struct common_audit_data ad;
 	struct file_security_struct *fsec = file->f_security;
 	struct inode *inode = file_inode(file);
-	struct inode_security_struct *isec = inode_security(inode);
+	struct inode_security_struct *isec;
 	struct lsm_ioctlop_audit ioctl;
 	u32 ssid = cred_sid(cred);
 	int rc;
@@ -3344,6 +3348,7 @@ static int ioctl_has_perm(const struct cred *cred, struct file *file,
 	if (unlikely(IS_PRIVATE(inode)))
 		return 0;
 
+	isec = inode_security(inode);
 	rc = avc_has_extended_perms(ssid, isec->sid, isec->sclass,
 			requested, driver, xperm, &ad);
 out:
@@ -3745,18 +3750,18 @@ static int selinux_kernel_module_from_file(struct file *file)
 					SYSTEM__MODULE_LOAD, NULL);
 
 	/* finit_module */
+
 	ad.type = LSM_AUDIT_DATA_PATH;
 	ad.u.path = file->f_path;
 
-	isec = inode_security(file_inode(file));
 	fsec = file->f_security;
-
 	if (sid != fsec->sid) {
 		rc = avc_has_perm(sid, fsec->sid, SECCLASS_FD, FD__USE, &ad);
 		if (rc)
 			return rc;
 	}
 
+	isec = inode_security(file_inode(file));
 	return avc_has_perm(sid, isec->sid, SECCLASS_SYSTEM,
 				SYSTEM__MODULE_LOAD, &ad);
 }