ResStringPool: Fix security vulnerability

[android-x86/frameworks-base.git] / libs / androidfw / ResourceTypes.cpp

diff --git a/libs/androidfw/ResourceTypes.cpp b/libs/androidfw/ResourceTypes.cpp
index 0782269..401c7b0 100644 (file)
--- a/libs/androidfw/ResourceTypes.cpp
+++ b/libs/androidfw/ResourceTypes.cpp
@@ -457,6 +457,22 @@ status_t ResStringPool::setTo(const void* data, size_t size, bool copyData)
 
     uninit();
 
+    // The chunk must be at least the size of the string pool header.
+    if (size < sizeof(ResStringPool_header)) {
+        LOG_ALWAYS_FATAL("Bad string block: data size %zu is too small to be a string block", size);
+        return (mError=BAD_TYPE);
+    }
+
+    // The data is at least as big as a ResChunk_header, so we can safely validate the other
+    // header fields.
+    // `data + size` is safe because the source of `size` comes from the kernel/filesystem.
+    if (validate_chunk(reinterpret_cast<const ResChunk_header*>(data), sizeof(ResStringPool_header),
+                       reinterpret_cast<const uint8_t*>(data) + size,
+                       "ResStringPool_header") != NO_ERROR) {
+        LOG_ALWAYS_FATAL("Bad string block: malformed block dimensions");
+        return (mError=BAD_TYPE);
+    }
+
     const bool notDeviceEndian = htods(0xf0) != 0xf0;
 
     if (copyData || notDeviceEndian) {
@@ -468,6 +484,8 @@ status_t ResStringPool::setTo(const void* data, size_t size, bool copyData)
         data = mOwnedData;
     }
 
+    // The size has been checked, so it is safe to read the data in the ResStringPool_header
+    // data structure.
     mHeader = (const ResStringPool_header*)data;
 
     if (notDeviceEndian) {
@@ -813,7 +831,13 @@ const char* ResStringPool::string8At(size_t idx, size_t* outLen) const
             *outLen = encLen;
 
             if ((uint32_t)(str+encLen-strings) < mStringPoolSize) {
-                return (const char*)str;
+                // Reject malformed (non null-terminated) strings
+                if (str[encLen] != 0x00) {
+                    ALOGW("Bad string block: string #%d is not null-terminated",
+                          (int)idx);
+                    return NULL;
+                }
+              return (const char*)str;
             } else {
                 ALOGW("Bad string block: string #%d extends to %d, past end at %d\n",
                         (int)idx, (int)(str+encLen-strings), (int)mStringPoolSize);