1 /*
2  * Copyright (C) 2023 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package android.content.res;
18 
19 import android.annotation.NonNull;
20 import android.annotation.StyleableRes;
21 
22 import com.android.internal.R;
23 
24 import org.xmlpull.v1.XmlPullParser;
25 import org.xmlpull.v1.XmlPullParserException;
26 
27 import java.util.ArrayDeque;
28 
29 /**
30  * Validates manifest files by ensuring that tag counts and the length of string attributes are
31  * restricted.
32  *
33  * {@hide}
34  */
35 public class Validator {
36 
37     private final ArrayDeque<Element> mElements = new ArrayDeque<>();
38 
cleanUp()39     private void cleanUp() {
40         while (!mElements.isEmpty()) {
41             mElements.pop().recycle();
42         }
43     }
44 
45     /**
46      * Validates the elements and it's attributes as the XmlPullParser traverses the xml.
47      */
validate(@onNull XmlPullParser parser)48     public void validate(@NonNull XmlPullParser parser) throws XmlPullParserException {
49         int eventType = parser.getEventType();
50         int depth = parser.getDepth();
51         // The mElement size should equal to the parser depth-1 when the parser eventType is
52         // START_TAG. If depth - mElement.size() is larger than 1 then that means
53         // validation for the previous element was skipped so we should skip validation for all
54         // descendant elements as well
55         if (depth > mElements.size() + 1) {
56             return;
57         }
58         if (eventType == XmlPullParser.START_TAG) {
59             String tag = parser.getName();
60             if (Element.shouldValidate(tag)) {
61                 Element element = Element.obtain(tag);
62                 Element parent = mElements.peek();
63                 if (parent != null && parent.hasChild(tag)) {
64                     try {
65                         parent.seen(element);
66                     } catch (SecurityException e) {
67                         cleanUp();
68                         throw e;
69                     }
70                 }
71                 mElements.push(element);
72             }
73         } else if (eventType == XmlPullParser.END_TAG && depth == mElements.size()) {
74             mElements.pop().recycle();
75         } else if (eventType == XmlPullParser.END_DOCUMENT) {
76             cleanUp();
77         }
78     }
79 
80     /**
81      * Validates the resource string of a manifest tag attribute.
82      */
validateResStrAttr(@onNull XmlPullParser parser, @StyleableRes int index, CharSequence stringValue)83     public void validateResStrAttr(@NonNull XmlPullParser parser, @StyleableRes int index,
84             CharSequence stringValue) {
85         if (parser.getDepth() > mElements.size()) {
86             return;
87         }
88         mElements.peek().validateResStrAttr(index, stringValue);
89         if (index == R.styleable.AndroidManifestMetaData_value) {
90             validateComponentMetadata(stringValue.toString());
91         }
92     }
93 
94     /**
95      * Validates the string of a manifest tag attribute by name.
96      */
validateStrAttr(@onNull XmlPullParser parser, String attrName, String attrValue)97     public void validateStrAttr(@NonNull XmlPullParser parser, String attrName, String attrValue) {
98         if (parser.getDepth() > mElements.size()) {
99             return;
100         }
101         mElements.peek().validateStrAttr(attrName, attrValue);
102         if (attrName.equals(Element.TAG_ATTR_VALUE)) {
103             validateComponentMetadata(attrValue);
104         }
105     }
106 
validateComponentMetadata(String attrValue)107     private void validateComponentMetadata(String attrValue) {
108         Element element = mElements.peek();
109         // Meta-data values are evaluated on the parent element which is the next element in the
110         // mElements stack after the meta-data element. The top of the stack is always the current
111         // element being validated so check that the top element is meta-data.
112         if (element.mTag.equals(Element.TAG_META_DATA) && mElements.size() > 1) {
113             element = mElements.pop();
114             mElements.peek().validateComponentMetadata(attrValue);
115             mElements.push(element);
116         }
117     }
118 }
119