udf: Implement searching for directory entry using new iteration code

Implement searching for directory entry - udf_fiiter_find_entry() -
using new directory iteration code.

Reported-by: syzbot+69c9fdccc6dd08961d34@syzkaller.appspotmail.com
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/namei.c

@@ -140,6 +140,73 @@ int udf_write_fi(struct inode *inode, struct fileIdentDesc *cfi,
 	return 0;
 }
 
+/**
+ * udf_fiiter_find_entry - find entry in given directory.
+ *
+ * @dir:	directory inode to search in
+ * @child:	qstr of the name
+ * @iter:	iter to use for searching
+ *
+ * This function searches in the directory @dir for a file name @child. When
+ * found, @iter points to the position in the directory with given entry.
+ *
+ * Returns 0 on success, < 0 on error (including -ENOENT).
+ */
+static int udf_fiiter_find_entry(struct inode *dir, const struct qstr *child,
+				 struct udf_fileident_iter *iter)
+{
+	int flen;
+	unsigned char *fname = NULL;
+	struct super_block *sb = dir->i_sb;
+	int isdotdot = child->len == 2 &&
+		child->name[0] == '.' && child->name[1] == '.';
+	int ret;
+
+	fname = kmalloc(UDF_NAME_LEN, GFP_NOFS);
+	if (!fname)
+		return -ENOMEM;
+
+	for (ret = udf_fiiter_init(iter, dir, 0);
+	     !ret && iter->pos < dir->i_size;
+	     ret = udf_fiiter_advance(iter)) {
+		if (iter->fi.fileCharacteristics & FID_FILE_CHAR_DELETED) {
+			if (!UDF_QUERY_FLAG(sb, UDF_FLAG_UNDELETE))
+				continue;
+		}
+
+		if (iter->fi.fileCharacteristics & FID_FILE_CHAR_HIDDEN) {
+			if (!UDF_QUERY_FLAG(sb, UDF_FLAG_UNHIDE))
+				continue;
+		}
+
+		if ((iter->fi.fileCharacteristics & FID_FILE_CHAR_PARENT) &&
+		    isdotdot)
+			goto out_ok;
+
+		if (!iter->fi.lengthFileIdent)
+			continue;
+
+		flen = udf_get_filename(sb, iter->name,
+				iter->fi.lengthFileIdent, fname, UDF_NAME_LEN);
+		if (flen < 0) {
+			ret = flen;
+			goto out_err;
+		}
+
+		if (udf_match(flen, fname, child->len, child->name))
+			goto out_ok;
+	}
+	if (!ret)
+		ret = -ENOENT;
+
+out_err:
+	udf_fiiter_release(iter);
+out_ok:
+	kfree(fname);
+
+	return ret;
+}
+
 /**
  * udf_find_entry - find entry in given directory.
  *