From a720635be20f4fc3acd39c7b83b919140ced0f94 Mon Sep 17 00:00:00 2001
From: Fabien Sanglard <sanglardf@google.com>
Date: Tue, 20 Oct 2020 15:47:10 -0700
Subject: Fix zipalign alignment error

Problem: Zipalign operates over several false assumptions. First it
assumes that zip entries are in the same order in the body and in
the Central Direcotry. Second, it assumes there are not space
between entries. This makes alignment incorrect when these asserts
are not true.

Solution: Don't align entries by tracking bias based on input zip
entry location. Calculate the expected alignment based on the out-
put zip file and correct with extra padding.

Fixes: 162117652
Test: Units Tests
Change-Id: Ia179338f658cab18a377cba2c7c8e629089a2785
---
 tools/zipalign/ZipFile.cpp | 37 +++++++++++++++++++++++++++++++------
 1 file changed, 31 insertions(+), 6 deletions(-)

(limited to 'tools/zipalign/ZipFile.cpp')

diff --git a/tools/zipalign/ZipFile.cpp b/tools/zipalign/ZipFile.cpp
index 29d1bc6849..9938a06088 100644
--- a/tools/zipalign/ZipFile.cpp
+++ b/tools/zipalign/ZipFile.cpp
@@ -502,6 +502,32 @@ bail:
     return result;
 }
 
+/*
+ * Based on the current position in the output zip, assess where the entry
+ * payload will end up if written as-is. If alignment is not satisfactory,
+ * add some padding in the extra field.
+ *
+ */
+status_t ZipFile::alignEntry(android::ZipEntry* pEntry, uint32_t alignTo){
+    if (alignTo == 0 || alignTo == 1)
+        return OK;
+
+    // Calculate where the entry payload offset will end up if we were to write
+    // it as-is.
+    uint64_t expectedPayloadOffset = ftell(mZipFp) +
+        android::ZipEntry::LocalFileHeader::kLFHLen +
+        pEntry->mLFH.mFileNameLength +
+        pEntry->mLFH.mExtraFieldLength;
+
+    // If the alignment is not what was requested, add some padding in the extra
+    // so the payload ends up where is requested.
+    uint64_t alignDiff = alignTo - (expectedPayloadOffset % alignTo);
+    if (alignDiff == 0)
+        return OK;
+
+    return pEntry->addPadding(alignDiff);
+}
+
 /*
  * Add an entry by copying it from another zip file.  If "padding" is
  * nonzero, the specified number of bytes will be added to the "extra"
@@ -510,7 +536,7 @@ bail:
  * If "ppEntry" is non-NULL, a pointer to the new entry will be returned.
  */
 status_t ZipFile::add(const ZipFile* pSourceZip, const ZipEntry* pSourceEntry,
-    int padding, ZipEntry** ppEntry)
+    int alignTo, ZipEntry** ppEntry)
 {
     ZipEntry* pEntry = NULL;
     status_t result;
@@ -537,11 +563,10 @@ status_t ZipFile::add(const ZipFile* pSourceZip, const ZipEntry* pSourceEntry,
     result = pEntry->initFromExternal(pSourceEntry);
     if (result != OK)
         goto bail;
-    if (padding != 0) {
-        result = pEntry->addPadding(padding);
-        if (result != OK)
-            goto bail;
-    }
+
+    result = alignEntry(pEntry, alignTo);
+    if (result != OK)
+      goto bail;
 
     /*
      * From here on out, failures are more interesting.
-- 
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