Bug 1832591: Add CRCs to preloader caches. r=mccr8

We've been seeing crashes in the wild from multiple entries with empty hash
key names being read from the preloader caches. Based on assertions we've
added to the code, it appears that this is happening on disk, after the cache
has been written, rather than during runtime.

Using a CRC for this sort of data is a sensible precaution in any case, and it
should make it easier to distinguish between on-disk corruption that we can
safely ignore and other sorts of consistency issues that we should ideally
fix.

Differential Revision: https://phabricator.services.mozilla.com/D178118

js/xpconnect/loader/ScriptPreloader.cpp

@@ -26,6 +26,7 @@
 #include "mozilla/dom/ContentParent.h"
 #include "mozilla/dom/Document.h"
 
+#include "crc32c.h"
 #include "js/CompileOptions.h"  // JS::ReadOnlyCompileOptions
 #include "js/experimental/JSStencil.h"
 #include "js/Transcoding.h"
@@ -401,7 +402,7 @@ Result<nsCOMPtr<nsIFile>, nsresult> ScriptPreloader::GetCacheFile(
   return std::move(cacheFile);
 }
 
-static const uint8_t MAGIC[] = "mozXDRcachev002";
+static const uint8_t MAGIC[] = "mozXDRcachev003";
 
 Result<Ok, nsresult> ScriptPreloader::OpenCache() {
   MOZ_TRY(NS_GetSpecialDirectory("ProfLDS", getter_AddRefs(mProfD)));
@@ -510,7 +511,8 @@ Result<Ok, nsresult> ScriptPreloader::InitCacheInternal(
   auto size = mCacheData->size();
 
   uint32_t headerSize;
-  if (size < sizeof(MAGIC) + sizeof(headerSize)) {
+  uint32_t crc;
+  if (size < sizeof(MAGIC) + sizeof(headerSize) + sizeof(crc)) {
     return Err(NS_ERROR_UNEXPECTED);
   }
 
@@ -527,10 +529,17 @@ Result<Ok, nsresult> ScriptPreloader::InitCacheInternal(
   headerSize = LittleEndian::readUint32(data.get());
   data += sizeof(headerSize);
 
+  crc = LittleEndian::readUint32(data.get());
+  data += sizeof(crc);
+
   if (data + headerSize > end) {
     return Err(NS_ERROR_UNEXPECTED);
   }
 
+  if (crc != ComputeCrc32c(~0, data.get(), headerSize)) {
+    return Err(NS_ERROR_UNEXPECTED);
+  }
+
   {
     auto cleanup = MakeScopeExit([&]() { mScripts.Clear(); });
 
@@ -726,8 +735,12 @@ Result<Ok, nsresult> ScriptPreloader::WriteCache() {
     uint8_t headerSize[4];
     LittleEndian::writeUint32(headerSize, buf.cursor());
 
+    uint8_t crc[4];
+    LittleEndian::writeUint32(crc, ComputeCrc32c(~0, buf.Get(), buf.cursor()));
+
     MOZ_TRY(Write(fd, MAGIC, sizeof(MAGIC)));
     MOZ_TRY(Write(fd, headerSize, sizeof(headerSize)));
+    MOZ_TRY(Write(fd, crc, sizeof(crc)));
     MOZ_TRY(Write(fd, buf.Get(), buf.cursor()));
 
     // Align the start of the scripts section to the transcode alignment.

js/xpconnect/loader/URLPreloader.cpp

@@ -18,6 +18,7 @@
 #include "mozilla/Unused.h"
 #include "mozilla/Vector.h"
 
+#include "crc32c.h"
 #include "MainThreadUtils.h"
 #include "nsPrintfCString.h"
 #include "nsDebug.h"
@@ -165,7 +166,7 @@ Result<nsCOMPtr<nsIFile>, nsresult> URLPreloader::GetCacheFile(
   return std::move(cacheFile);
 }
 
-static const uint8_t URL_MAGIC[] = "mozURLcachev002";
+static const uint8_t URL_MAGIC[] = "mozURLcachev003";
 
 Result<nsCOMPtr<nsIFile>, nsresult> URLPreloader::FindCacheFile() {
   nsCOMPtr<nsIFile> cacheFile;
@@ -235,8 +236,12 @@ Result<Ok, nsresult> URLPreloader::WriteCache() {
     uint8_t headerSize[4];
     LittleEndian::writeUint32(headerSize, buf.cursor());
 
+    uint8_t crc[4];
+    LittleEndian::writeUint32(crc, ComputeCrc32c(~0, buf.Get(), buf.cursor()));
+
     MOZ_TRY(Write(fd, URL_MAGIC, sizeof(URL_MAGIC)));
     MOZ_TRY(Write(fd, headerSize, sizeof(headerSize)));
+    MOZ_TRY(Write(fd, crc, sizeof(crc)));
     MOZ_TRY(Write(fd, buf.Get(), buf.cursor()));
   }
 
@@ -263,7 +268,8 @@ Result<Ok, nsresult> URLPreloader::ReadCache(
   auto size = cache.size();
 
   uint32_t headerSize;
-  if (size < sizeof(URL_MAGIC) + sizeof(headerSize)) {
+  uint32_t crc;
+  if (size < sizeof(URL_MAGIC) + sizeof(headerSize) + sizeof(crc)) {
     return Err(NS_ERROR_UNEXPECTED);
   }
 
@@ -278,10 +284,17 @@ Result<Ok, nsresult> URLPreloader::ReadCache(
   headerSize = LittleEndian::readUint32(data.get());
   data += sizeof(headerSize);
 
+  crc = LittleEndian::readUint32(data.get());
+  data += sizeof(crc);
+
   if (data + headerSize > end) {
     return Err(NS_ERROR_UNEXPECTED);
   }
 
+  if (crc != ComputeCrc32c(~0, data.get(), headerSize)) {
+    return Err(NS_ERROR_UNEXPECTED);
+  }
+
   {
     mMonitor.AssertCurrentThreadOwns();
 

js/xpconnect/loader/moz.build

@@ -61,6 +61,7 @@ LOCAL_INCLUDES += [
     "/dom/base",
     "/js/loader",
     "/xpcom/base/",
+    "/xpcom/io",  # crc32c.h
 ]
 
 include("/ipc/chromium/chromium-config.mozbuild")