30481342: Security Vulnerability - TOCTOU in MmsProvider allows access to files as phone (radio) uid
Problem: MmsProvider.openFile validated the current _data column
in the DB and then called ContentProvider.openFileHelper which was again
reading from the DB. A race condition could cause the second DB read to
read an updated, malicious value.
Fix: instead of doing the first DB check and calling
ContentProvider.openFileHelper, we're now just calling
MmsProvider.safeOpenFileHelper which does a single check.
Test: used the POC provided for this incident.
b/30481342
Change-Id: I653129359130b9fae59d4c355320b266c158a698
(cherry picked from commit 5bc7f9682d72c89ba252be6471b2db9b7e7815e3)
diff --git a/src/com/android/providers/telephony/MmsProvider.java b/src/com/android/providers/telephony/MmsProvider.java
index 5acfe13..71e84c6 100644
--- a/src/com/android/providers/telephony/MmsProvider.java
+++ b/src/com/android/providers/telephony/MmsProvider.java
@@ -16,6 +16,7 @@
package com.android.providers.telephony;
+import android.annotation.NonNull;
import android.app.AppOpsManager;
import android.content.ContentProvider;
import android.content.ContentValues;
@@ -301,7 +302,11 @@
@Override
public Uri insert(Uri uri, ContentValues values) {
- // Don't let anyone insert anything with the _data column
+ // The _data column is filled internally in MmsProvider, so this check is just to avoid
+ // it from being inadvertently set. This is not supposed to be a protection against
+ // malicious attack, since sql injection could still be attempted to bypass the check. On
+ // the other hand, the MmsProvider does verify that the _data column has an allowed value
+ // before opening any uri/files.
if (values != null && values.containsKey(Part._DATA)) {
return null;
}
@@ -726,9 +731,12 @@
}
@Override
- public int update(Uri uri, ContentValues values,
- String selection, String[] selectionArgs) {
- // Don't let anyone update the _data column
+ public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
+ // The _data column is filled internally in MmsProvider, so this check is just to avoid
+ // it from being inadvertently set. This is not supposed to be a protection against
+ // malicious attack, since sql injection could still be attempted to bypass the check. On
+ // the other hand, the MmsProvider does verify that the _data column has an allowed value
+ // before opening any uri/files.
if (values != null && values.containsKey(Part._DATA)) {
return 0;
}
@@ -834,7 +842,12 @@
return null;
}
- // Verify that the _data path points to mms data
+ return safeOpenFileHelper(uri, mode);
+ }
+
+ @NonNull
+ private ParcelFileDescriptor safeOpenFileHelper(
+ @NonNull Uri uri, @NonNull String mode) throws FileNotFoundException {
Cursor c = query(uri, new String[]{"_data"}, null, null, null);
int count = (c != null) ? c.getCount() : 0;
if (count != 1) {
@@ -855,10 +868,16 @@
c.close();
if (path == null) {
- return null;
+ throw new FileNotFoundException("Column _data not found.");
}
+
+ File filePath = new File(path);
try {
- File filePath = new File(path);
+ // The MmsProvider shouldn't open a file that isn't MMS data, so we verify that the
+ // _data path actually points to MMS data. That safeguards ourselves from callers who
+ // inserted or updated a URI (more specifically the _data column) with disallowed paths.
+ // TODO(afurtado): provide a more robust mechanism to avoid disallowed _data paths to
+ // be inserted/updated in the first place, including via SQL injection.
if (!filePath.getCanonicalPath()
.startsWith(getContext().getDir(PARTS_DIR_NAME, 0).getCanonicalPath())) {
Log.e(TAG, "openFile: path "
@@ -866,7 +885,6 @@
+ " does not start with "
+ getContext().getDir(PARTS_DIR_NAME, 0).getCanonicalPath());
// Don't care return value
- filePath.delete();
return null;
}
} catch (IOException e) {
@@ -874,7 +892,8 @@
return null;
}
- return openFileHelper(uri, mode);
+ int modeBits = ParcelFileDescriptor.parseMode(mode);
+ return ParcelFileDescriptor.open(filePath, modeBits);
}
private void filterUnsupportedKeys(ContentValues values) {
