bpf: reject invalid names right in ->lookup()

... and other methods won't see them at all
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

kernel/bpf/inode.c

@@ -119,18 +119,10 @@ static int bpf_inode_type(const struct inode *inode, enum bpf_type *type)
 	return 0;
 }
 
-static bool bpf_dname_reserved(const struct dentry *dentry)
-{
-	return strchr(dentry->d_name.name, '.');
-}
-
 static int bpf_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 {
 	struct inode *inode;
 
-	if (bpf_dname_reserved(dentry))
-		return -EPERM;
-
 	inode = bpf_get_inode(dir->i_sb, dir, mode | S_IFDIR);
 	if (IS_ERR(inode))
 		return PTR_ERR(inode);
@@ -152,9 +144,6 @@ static int bpf_mkobj_ops(struct inode *dir, struct dentry *dentry,
 {
 	struct inode *inode;
 
-	if (bpf_dname_reserved(dentry))
-		return -EPERM;
-
 	inode = bpf_get_inode(dir->i_sb, dir, mode | S_IFREG);
 	if (IS_ERR(inode))
 		return PTR_ERR(inode);
@@ -187,31 +176,21 @@ static int bpf_mkobj(struct inode *dir, struct dentry *dentry, umode_t mode,
 	}
 }
 
-static int bpf_link(struct dentry *old_dentry, struct inode *dir,
-		    struct dentry *new_dentry)
+static struct dentry *
+bpf_lookup(struct inode *dir, struct dentry *dentry, unsigned flags)
 {
-	if (bpf_dname_reserved(new_dentry))
-		return -EPERM;
-
-	return simple_link(old_dentry, dir, new_dentry);
-}
-
-static int bpf_rename(struct inode *old_dir, struct dentry *old_dentry,
-		      struct inode *new_dir, struct dentry *new_dentry)
-{
-	if (bpf_dname_reserved(new_dentry))
-		return -EPERM;
-
-	return simple_rename(old_dir, old_dentry, new_dir, new_dentry);
+	if (strchr(dentry->d_name.name, '.'))
+		return ERR_PTR(-EPERM);
+	return simple_lookup(dir, dentry, flags);
 }
 
 static const struct inode_operations bpf_dir_iops = {
-	.lookup		= simple_lookup,
+	.lookup		= bpf_lookup,
 	.mknod		= bpf_mkobj,
 	.mkdir		= bpf_mkdir,
 	.rmdir		= simple_rmdir,
-	.rename		= bpf_rename,
-	.link		= bpf_link,
+	.rename		= simple_rename,
+	.link		= simple_link,
 	.unlink		= simple_unlink,
 };