ResStringPool: Fix security vulnerability

Adds detection of attacker-modified size and data fields passed to
ResStringPool::setTo(). These attacks are modified apks that AAPT would
not normally generate. In the rare case this occurs, the installation
cannot be allowed to continue.

Bug: 71361168
Bug: 71360999
Test: run cts -m CtsAppSecurityHostTestCases \
          -t android.appsecurity.cts.CorruptApkTests

Change-Id: If7eb93a9e723b16c8a0556fc4e20006aa0391d57
Merged-In: If7eb93a9e723b16c8a0556fc4e20006aa0391d57
(cherry picked from commit 7e54c3f261d81316b75cb734075319108d8bc1d1)
CVE-2018-9338, CVE-2018-9340

1 files changed, 18 insertions, 0 deletions

diff --git a/libs/androidfw/ResourceTypes.cpp b/libs/androidfw/ResourceTypes.cpp
index 5b04eb9f05c..109619bf84a 100644
--- a/libs/androidfw/ResourceTypes.cpp
+++ b/libs/androidfw/ResourceTypes.cpp
@@ -464,6 +464,22 @@ 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) {
@@ -475,6 +491,8 @@ 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) {