diff --git a/src/com/android/providers/telephony/MmsSmsProvider.java b/src/com/android/providers/telephony/MmsSmsProvider.java
index 8c3555c..dbf85ae 100644
--- a/src/com/android/providers/telephony/MmsSmsProvider.java
+++ b/src/com/android/providers/telephony/MmsSmsProvider.java
@@ -332,6 +332,16 @@
         final String pduTable = MmsProvider.getPduTable(accessRestricted);
         final String smsTable = SmsProvider.getSmsTable(accessRestricted);
 
+        // If access is restricted, we don't allow subqueries in the query.
+        if (accessRestricted) {
+            try {
+                SqlQueryChecker.checkQueryParametersForSubqueries(projection, selection, sortOrder);
+            } catch (IllegalArgumentException e) {
+                Log.w(LOG_TAG, "Query rejected: " + e.getMessage());
+                return null;
+            }
+        }
+
         SQLiteDatabase db = mOpenHelper.getReadableDatabase();
         Cursor cursor = null;
         final int match = URI_MATCHER.match(uri);
diff --git a/src/com/android/providers/telephony/SQLiteTokenizer.java b/src/com/android/providers/telephony/SQLiteTokenizer.java
new file mode 100644
index 0000000..39749fb
--- /dev/null
+++ b/src/com/android/providers/telephony/SQLiteTokenizer.java
@@ -0,0 +1,297 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.providers.telephony;
+
+import android.annotation.NonNull;
+import android.annotation.Nullable;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Locale;
+import java.util.function.Consumer;
+
+/**
+ * Copied from frameworks/base/core/java/android/database/sqlite/SQLiteTokenizer.java
+ *
+ * SQL Tokenizer specialized to extract tokens from SQL (snippets).
+ * <p>
+ * Based on sqlite3GetToken() in tokenzie.c in SQLite.
+ * <p>
+ * Source for v3.8.6 (which android uses): http://www.sqlite.org/src/artifact/ae45399d6252b4d7
+ * (Latest source as of now: http://www.sqlite.org/src/artifact/78c8085bc7af1922)
+ * <p>
+ * Also draft spec: http://www.sqlite.org/draft/tokenreq.html
+ */
+public class SQLiteTokenizer {
+    private static boolean isAlpha(char ch) {
+        return ('a' <= ch && ch <= 'z') || ('A' <= ch && ch <= 'Z') || (ch == '_');
+    }
+
+    private static boolean isNum(char ch) {
+        return ('0' <= ch && ch <= '9');
+    }
+
+    private static boolean isAlNum(char ch) {
+        return isAlpha(ch) || isNum(ch);
+    }
+
+    private static boolean isAnyOf(char ch, String set) {
+        return set.indexOf(ch) >= 0;
+    }
+
+    private static IllegalArgumentException genException(String message, String sql) {
+        throw new IllegalArgumentException(message + " in '" + sql + "'");
+    }
+
+    private static char peek(String s, int index) {
+        return index < s.length() ? s.charAt(index) : '\0';
+    }
+
+    public static final int OPTION_NONE = 0;
+
+    /**
+     * Require that SQL contains only tokens; any comments or values will result
+     * in an exception.
+     */
+    public static final int OPTION_TOKEN_ONLY = 1 << 0;
+
+    /**
+     * Tokenize the given SQL, returning the list of each encountered token.
+     *
+     * @throws IllegalArgumentException if invalid SQL is encountered.
+     */
+    public static List<String> tokenize(@Nullable String sql, int options) {
+        final ArrayList<String> res = new ArrayList<>();
+        tokenize(sql, options, res::add);
+        return res;
+    }
+
+    /**
+     * Tokenize the given SQL, sending each encountered token to the given
+     * {@link Consumer}.
+     *
+     * @throws IllegalArgumentException if invalid SQL is encountered.
+     */
+    public static void tokenize(@Nullable String sql, int options, Consumer<String> checker) {
+        if (sql == null) {
+            return;
+        }
+        int pos = 0;
+        final int len = sql.length();
+        while (pos < len) {
+            final char ch = peek(sql, pos);
+
+            // Regular token.
+            if (isAlpha(ch)) {
+                final int start = pos;
+                pos++;
+                while (isAlNum(peek(sql, pos))) {
+                    pos++;
+                }
+                final int end = pos;
+
+                final String token = sql.substring(start, end);
+                checker.accept(token);
+
+                continue;
+            }
+
+            // Handle quoted tokens
+            if (isAnyOf(ch, "'\"`")) {
+                final int quoteStart = pos;
+                pos++;
+
+                for (;;) {
+                    pos = sql.indexOf(ch, pos);
+                    if (pos < 0) {
+                        throw genException("Unterminated quote", sql);
+                    }
+                    if (peek(sql, pos + 1) != ch) {
+                        break;
+                    }
+                    // Quoted quote char -- e.g. "abc""def" is a single string.
+                    pos += 2;
+                }
+                final int quoteEnd = pos;
+                pos++;
+
+                if (ch != '\'') {
+                    // Extract the token
+                    final String tokenUnquoted = sql.substring(quoteStart + 1, quoteEnd);
+
+                    final String token;
+
+                    // Unquote if needed. i.e. "aa""bb" -> aa"bb
+                    if (tokenUnquoted.indexOf(ch) >= 0) {
+                        token = tokenUnquoted.replaceAll(
+                                String.valueOf(ch) + ch, String.valueOf(ch));
+                    } else {
+                        token = tokenUnquoted;
+                    }
+                    checker.accept(token);
+                } else {
+                    if ((options &= OPTION_TOKEN_ONLY) != 0) {
+                        throw genException("Non-token detected", sql);
+                    }
+                }
+                continue;
+            }
+            // Handle tokens enclosed in [...]
+            if (ch == '[') {
+                final int quoteStart = pos;
+                pos++;
+
+                pos = sql.indexOf(']', pos);
+                if (pos < 0) {
+                    throw genException("Unterminated quote", sql);
+                }
+                final int quoteEnd = pos;
+                pos++;
+
+                final String token = sql.substring(quoteStart + 1, quoteEnd);
+
+                checker.accept(token);
+                continue;
+            }
+            if ((options &= OPTION_TOKEN_ONLY) != 0) {
+                throw genException("Non-token detected", sql);
+            }
+
+            // Detect comments.
+            if (ch == '-' && peek(sql, pos + 1) == '-') {
+                pos += 2;
+                pos = sql.indexOf('\n', pos);
+                if (pos < 0) {
+                    // We disallow strings ending in an inline comment.
+                    throw genException("Unterminated comment", sql);
+                }
+                pos++;
+
+                continue;
+            }
+            if (ch == '/' && peek(sql, pos + 1) == '*') {
+                pos += 2;
+                pos = sql.indexOf("*/", pos);
+                if (pos < 0) {
+                    throw genException("Unterminated comment", sql);
+                }
+                pos += 2;
+
+                continue;
+            }
+
+            // Semicolon is never allowed.
+            if (ch == ';') {
+                throw genException("Semicolon is not allowed", sql);
+            }
+
+            // For this purpose, we can simply ignore other characters.
+            // (Note it doesn't handle the X'' literal properly and reports this X as a token,
+            // but that should be fine...)
+            pos++;
+        }
+    }
+
+    /**
+     * Test if given token is a
+     * <a href="https://www.sqlite.org/lang_keywords.html">SQLite reserved
+     * keyword</a>.
+     */
+    public static boolean isKeyword(@NonNull String token) {
+        switch (token.toUpperCase(Locale.US)) {
+            case "ABORT": case "ACTION": case "ADD": case "AFTER":
+            case "ALL": case "ALTER": case "ANALYZE": case "AND":
+            case "AS": case "ASC": case "ATTACH": case "AUTOINCREMENT":
+            case "BEFORE": case "BEGIN": case "BETWEEN": case "BINARY":
+            case "BY": case "CASCADE": case "CASE": case "CAST":
+            case "CHECK": case "COLLATE": case "COLUMN": case "COMMIT":
+            case "CONFLICT": case "CONSTRAINT": case "CREATE": case "CROSS":
+            case "CURRENT": case "CURRENT_DATE": case "CURRENT_TIME": case "CURRENT_TIMESTAMP":
+            case "DATABASE": case "DEFAULT": case "DEFERRABLE": case "DEFERRED":
+            case "DELETE": case "DESC": case "DETACH": case "DISTINCT":
+            case "DO": case "DROP": case "EACH": case "ELSE":
+            case "END": case "ESCAPE": case "EXCEPT": case "EXCLUDE":
+            case "EXCLUSIVE": case "EXISTS": case "EXPLAIN": case "FAIL":
+            case "FILTER": case "FOLLOWING": case "FOR": case "FOREIGN":
+            case "FROM": case "FULL": case "GLOB": case "GROUP":
+            case "GROUPS": case "HAVING": case "IF": case "IGNORE":
+            case "IMMEDIATE": case "IN": case "INDEX": case "INDEXED":
+            case "INITIALLY": case "INNER": case "INSERT": case "INSTEAD":
+            case "INTERSECT": case "INTO": case "IS": case "ISNULL":
+            case "JOIN": case "KEY": case "LEFT": case "LIKE":
+            case "LIMIT": case "MATCH": case "NATURAL": case "NO":
+            case "NOCASE": case "NOT": case "NOTHING": case "NOTNULL":
+            case "NULL": case "OF": case "OFFSET": case "ON":
+            case "OR": case "ORDER": case "OTHERS": case "OUTER":
+            case "OVER": case "PARTITION": case "PLAN": case "PRAGMA":
+            case "PRECEDING": case "PRIMARY": case "QUERY": case "RAISE":
+            case "RANGE": case "RECURSIVE": case "REFERENCES": case "REGEXP":
+            case "REINDEX": case "RELEASE": case "RENAME": case "REPLACE":
+            case "RESTRICT": case "RIGHT": case "ROLLBACK": case "ROW":
+            case "ROWS": case "RTRIM": case "SAVEPOINT": case "SELECT":
+            case "SET": case "TABLE": case "TEMP": case "TEMPORARY":
+            case "THEN": case "TIES": case "TO": case "TRANSACTION":
+            case "TRIGGER": case "UNBOUNDED": case "UNION": case "UNIQUE":
+            case "UPDATE": case "USING": case "VACUUM": case "VALUES":
+            case "VIEW": case "VIRTUAL": case "WHEN": case "WHERE":
+            case "WINDOW": case "WITH": case "WITHOUT":
+                return true;
+            default:
+                return false;
+        }
+    }
+
+    /**
+     * Test if given token is a
+     * <a href="https://www.sqlite.org/lang_corefunc.html">SQLite reserved
+     * function</a>.
+     */
+    public static boolean isFunction(@NonNull String token) {
+        switch (token.toLowerCase(Locale.US)) {
+            case "abs": case "avg": case "char": case "coalesce":
+            case "count": case "glob": case "group_concat": case "hex":
+            case "ifnull": case "instr": case "length": case "like":
+            case "likelihood": case "likely": case "lower": case "ltrim":
+            case "max": case "min": case "nullif": case "random":
+            case "randomblob": case "replace": case "round": case "rtrim":
+            case "substr": case "sum": case "total": case "trim":
+            case "typeof": case "unicode": case "unlikely": case "upper":
+            case "zeroblob":
+                return true;
+            default:
+                return false;
+        }
+    }
+
+    /**
+     * Test if given token is a
+     * <a href="https://www.sqlite.org/datatype3.html">SQLite reserved type</a>.
+     */
+    public static boolean isType(@NonNull String token) {
+        switch (token.toUpperCase(Locale.US)) {
+            case "INT": case "INTEGER": case "TINYINT": case "SMALLINT":
+            case "MEDIUMINT": case "BIGINT": case "INT2": case "INT8":
+            case "CHARACTER": case "VARCHAR": case "NCHAR": case "NVARCHAR":
+            case "TEXT": case "CLOB": case "BLOB": case "REAL":
+            case "DOUBLE": case "FLOAT": case "NUMERIC": case "DECIMAL":
+            case "BOOLEAN": case "DATE": case "DATETIME":
+                return true;
+            default:
+                return false;
+        }
+    }
+}
diff --git a/src/com/android/providers/telephony/SmsProvider.java b/src/com/android/providers/telephony/SmsProvider.java
index e2e6d10..1213c37 100644
--- a/src/com/android/providers/telephony/SmsProvider.java
+++ b/src/com/android/providers/telephony/SmsProvider.java
@@ -122,6 +122,16 @@
         final String smsTable = getSmsTable(accessRestricted);
         SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
 
+        // If access is restricted, we don't allow subqueries in the query.
+        if (accessRestricted) {
+            try {
+                SqlQueryChecker.checkQueryParametersForSubqueries(projectionIn, selection, sort);
+            } catch (IllegalArgumentException e) {
+                Log.w(TAG, "Query rejected: " + e.getMessage());
+                return null;
+            }
+        }
+
         // Generate the body of the query.
         int match = sURLMatcher.match(url);
         SQLiteDatabase db = getReadableDatabase(match);
diff --git a/src/com/android/providers/telephony/SqlQueryChecker.java b/src/com/android/providers/telephony/SqlQueryChecker.java
new file mode 100644
index 0000000..a98dd25
--- /dev/null
+++ b/src/com/android/providers/telephony/SqlQueryChecker.java
@@ -0,0 +1,46 @@
+/*
+ * Copyright 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.providers.telephony;
+
+public class SqlQueryChecker {
+    private static final String SELECT_TOKEN = "select";
+
+    static void checkToken(String token) {
+        if (SELECT_TOKEN.equals(token.toLowerCase())) {
+            throw new IllegalArgumentException("SELECT token not allowed in query");
+        }
+    }
+
+    /**
+     * Check the query parameters to see if they contain subqueries. Throws an
+     * {@link IllegalArgumentException} if they do. See
+     * {@link android.content.ContentProvider#query} for the definitions of the arguments.
+     */
+    static void checkQueryParametersForSubqueries(String[] projection,
+            String selection, String sortOrder) {
+        if (projection != null) {
+            for (String proj : projection) {
+                SQLiteTokenizer.tokenize(proj, SQLiteTokenizer.OPTION_NONE,
+                        SqlQueryChecker::checkToken);
+            }
+        }
+        SQLiteTokenizer.tokenize(selection, SQLiteTokenizer.OPTION_NONE,
+                SqlQueryChecker::checkToken);
+        SQLiteTokenizer.tokenize(sortOrder, SQLiteTokenizer.OPTION_NONE,
+                SqlQueryChecker::checkToken);
+    }
+}