[scudo] Modify header corrupption error message

Update the error message to be explicit that this is likely due
to memory corruption.

In addition, check if the chunk header is all zero, which could mean
corruption or an attempt to free a pointer after the memory has been
released to the kernel. This case results in a slightly different
error message to also indicate this could still be a double free.

Author: cferris1000

compiler-rt/lib/scudo/standalone/chunk.h

@@ -125,7 +125,7 @@ inline void loadHeader(u32 Cookie, const void *Ptr,
   *NewUnpackedHeader = bit_cast<UnpackedHeader>(NewPackedHeader);
   if (UNLIKELY(NewUnpackedHeader->Checksum !=
                computeHeaderChecksum(Cookie, Ptr, NewUnpackedHeader)))
-    reportHeaderCorruption(const_cast<void *>(Ptr));
+    reportHeaderCorruption(NewUnpackedHeader, const_cast<void *>(Ptr));
 }
 
 inline bool isValid(u32 Cookie, const void *Ptr,

compiler-rt/lib/scudo/standalone/report.cpp

@@ -9,6 +9,7 @@
 #include "report.h"
 
 #include "atomic_helpers.h"
+#include "chunk.h"
 #include "string_utils.h"
 
 #include <stdarg.h>
@@ -65,9 +66,18 @@ void NORETURN reportInvalidFlag(const char *FlagType, const char *Value) {
 
 // The checksum of a chunk header is invalid. This could be caused by an
 // {over,under}write of the header, a pointer that is not an actual chunk.
-void NORETURN reportHeaderCorruption(void *Ptr) {
-  ScopedErrorReport Report;
-  Report.append("corrupted chunk header at address %p\n", Ptr);
+void NORETURN reportHeaderCorruption(void *Header, void *Ptr) {
+  ScopedErrorReport Report;
+  Report.append("corrupted chunk header at address %p", Ptr);
+  if (*static_cast<Chunk::PackedHeader *>(Header) == 0U) {
+    // Header all zero, which could indicate that this might be a pointer that
+    // has been double freed but the memory has been released to the kernel.
+    Report.append(": chunk header is zero and might indicate memory corruption "
+                  "or a double free\n",
+                  Ptr);
+  } else {
+    Report.append(": most likely due to memory corruption\n", Ptr);
+  }
 }
 
 // The allocator was compiled with parameters that conflict with field size

compiler-rt/lib/scudo/standalone/report.h

@@ -12,7 +12,6 @@
 #include "internal_defs.h"
 
 namespace scudo {
-
 // Reports are *fatal* unless stated otherwise.
 
 // Generic error, adds newline to end of message.
@@ -25,7 +24,7 @@ void NORETURN reportRawError(const char *Message);
 void NORETURN reportInvalidFlag(const char *FlagType, const char *Value);
 
 // Chunk header related errors.
-void NORETURN reportHeaderCorruption(void *Ptr);
+void NORETURN reportHeaderCorruption(void *Header, void *Ptr);
 
 // Sanity checks related error.
 void NORETURN reportSanityCheckError(const char *Field);

compiler-rt/lib/scudo/standalone/tests/report_test.cpp

@@ -8,6 +8,7 @@
 
 #include "tests/scudo_unit_test.h"
 
+#include "chunk.h"
 #include "report.h"
 
 TEST(ScudoReportDeathTest, Check) {
@@ -20,9 +21,11 @@ TEST(ScudoReportDeathTest, Check) {
 TEST(ScudoReportDeathTest, Generic) {
   // Potentially unused if EXPECT_DEATH isn't defined.
   UNUSED void *P = reinterpret_cast<void *>(0x42424242U);
+  UNUSED scudo::Chunk::PackedHeader Header = {};
   EXPECT_DEATH(scudo::reportError("TEST123"), "Scudo ERROR.*TEST123");
   EXPECT_DEATH(scudo::reportInvalidFlag("ABC", "DEF"), "Scudo ERROR.*ABC.*DEF");
-  EXPECT_DEATH(scudo::reportHeaderCorruption(P), "Scudo ERROR.*42424242");
+  EXPECT_DEATH(scudo::reportHeaderCorruption(&Header, P),
+               "Scudo ERROR.*42424242");
   EXPECT_DEATH(scudo::reportSanityCheckError("XYZ"), "Scudo ERROR.*XYZ");
   EXPECT_DEATH(scudo::reportAlignmentTooBig(123, 456), "Scudo ERROR.*123.*456");
   EXPECT_DEATH(scudo::reportAllocationSizeTooBig(123, 456, 789),
@@ -54,6 +57,19 @@ TEST(ScudoReportDeathTest, CSpecific) {
                "Scudo ERROR.*123.*456");
 }
 
+TEST(ScudoReportDeathTest, HeaderCorruption) {
+  UNUSED void *P = reinterpret_cast<void *>(0x42424242U);
+  UNUSED scudo::Chunk::PackedHeader Header = {};
+  EXPECT_DEATH(scudo::reportHeaderCorruption(&Header, P),
+               "Scudo ERROR.*corrupted chunk header at address 0x.*42424242: "
+               "chunk header is zero and might indicate memory "
+               "corruption or a double free");
+  Header = 10U;
+  EXPECT_DEATH(scudo::reportHeaderCorruption(&Header, P),
+               "Scudo ERROR.*corrupted chunk header at address 0x.*42424242: "
+               "most likely due to memory corruption");
+}
+
 #if SCUDO_LINUX || SCUDO_TRUSTY || SCUDO_ANDROID
 #include "report_linux.h"