selinux: Implementation for inode_copy_up() hook

A file is being copied up for overlay file system. Prepare a new set of
creds and set create_sid appropriately so that new file is created with
appropriate label.

Overlay inode has right label for both context and non-context mount
cases. In case of non-context mount, overlay inode will have the label
of lower file and in case of context mount, overlay inode will have
the label from context= mount option.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/hooks.c

@@ -3293,6 +3293,26 @@ static void selinux_inode_getsecid(struct inode *inode, u32 *secid)
 	*secid = isec->sid;
 }
 
+static int selinux_inode_copy_up(struct dentry *src, struct cred **new)
+{
+	u32 sid;
+	struct task_security_struct *tsec;
+	struct cred *new_creds = *new;
+
+	if (new_creds == NULL) {
+		new_creds = prepare_creds();
+		if (!new_creds)
+			return -ENOMEM;
+	}
+
+	tsec = new_creds->security;
+	/* Get label from overlay inode and set it in create_sid */
+	selinux_inode_getsecid(d_inode(src), &sid);
+	tsec->create_sid = sid;
+	*new = new_creds;
+	return 0;
+}
+
 /* file security operations */
 
 static int selinux_revalidate_file_permission(struct file *file, int mask)
@@ -6088,6 +6108,7 @@ static struct security_hook_list selinux_hooks[] = {
 	LSM_HOOK_INIT(inode_setsecurity, selinux_inode_setsecurity),
 	LSM_HOOK_INIT(inode_listsecurity, selinux_inode_listsecurity),
 	LSM_HOOK_INIT(inode_getsecid, selinux_inode_getsecid),
+	LSM_HOOK_INIT(inode_copy_up, selinux_inode_copy_up),
 
 	LSM_HOOK_INIT(file_permission, selinux_file_permission),
 	LSM_HOOK_INIT(file_alloc_security, selinux_file_alloc_security),