ovl: define ->get_acl() for overlay inodes

Now we are planning to do DAC permission checks on overlay inode
itself. And to make it work, we will need to make sure we can get acls from
underlying inode. So define ->get_acl() for overlay inodes and this in turn
calls into underlying filesystem to get acls, if any.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/dir.c

@@ -921,4 +921,5 @@ const struct inode_operations ovl_dir_inode_operations = {
 	.getxattr	= ovl_getxattr,
 	.listxattr	= ovl_listxattr,
 	.removexattr	= ovl_removexattr,
+	.get_acl	= ovl_get_acl,
 };

fs/overlayfs/inode.c

@@ -310,6 +310,22 @@ int ovl_removexattr(struct dentry *dentry, const char *name)
 	return err;
 }
 
+struct posix_acl *ovl_get_acl(struct inode *inode, int type)
+{
+	struct inode *realinode = ovl_inode_real(inode);
+
+	if (!realinode)
+		return ERR_PTR(-ENOENT);
+
+	if (!IS_POSIXACL(realinode))
+		return NULL;
+
+	if (!realinode->i_op->get_acl)
+		return NULL;
+
+	return realinode->i_op->get_acl(realinode, type);
+}
+
 static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
 				  struct dentry *realdentry)
 {
@@ -354,6 +370,7 @@ static const struct inode_operations ovl_file_inode_operations = {
 	.getxattr	= ovl_getxattr,
 	.listxattr	= ovl_listxattr,
 	.removexattr	= ovl_removexattr,
+	.get_acl	= ovl_get_acl,
 };
 
 static const struct inode_operations ovl_symlink_inode_operations = {

fs/overlayfs/overlayfs.h

@@ -142,6 +142,7 @@ struct dentry *ovl_dentry_upper(struct dentry *dentry);
 struct dentry *ovl_dentry_lower(struct dentry *dentry);
 struct dentry *ovl_dentry_real(struct dentry *dentry);
 struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper);
+struct inode *ovl_inode_real(struct inode *inode);
 struct vfsmount *ovl_entry_mnt_real(struct ovl_entry *oe, struct inode *inode,
 				    bool is_upper);
 struct ovl_dir_cache *ovl_dir_cache(struct dentry *dentry);
@@ -179,6 +180,7 @@ ssize_t ovl_getxattr(struct dentry *dentry, struct inode *inode,
 		     const char *name, void *value, size_t size);
 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size);
 int ovl_removexattr(struct dentry *dentry, const char *name);
+struct posix_acl *ovl_get_acl(struct inode *inode, int type);
 int ovl_open_maybe_copy_up(struct dentry *dentry, unsigned int file_flags);
 
 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode,

fs/overlayfs/super.c

@@ -159,6 +159,13 @@ struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper)
 	return realdentry;
 }
 
+struct inode *ovl_inode_real(struct inode *inode)
+{
+	bool tmp;
+
+	return d_inode(ovl_entry_real(inode->i_private, &tmp));
+}
+
 struct vfsmount *ovl_entry_mnt_real(struct ovl_entry *oe, struct inode *inode,
 				    bool is_upper)
 {
@@ -1172,6 +1179,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	sb->s_op = &ovl_super_operations;
 	sb->s_root = root_dentry;
 	sb->s_fs_info = ufs;
+	sb->s_flags |= MS_POSIXACL;
 
 	return 0;