Improve resiliency in the face of memory corruption (arrays/strings w…

…ith invalid length) Summary: We have a few memory snapshots with unexpected/inconsistent contents in them (possibly due to memory corruption). We can report better warnings for strings/arrays with invalid length, and avoid a crash when dumping a string with an invalid length. Differential Revision: D56714330 fbshipit-source-id: 2d8c0b27cb0b1681e41bb9cc005b2cb98c912147
facebookexperimental · Apr 29, 2024 · b3ecb7c · b3ecb7c
1 parent dbf8e6c
commit b3ecb7c
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Showing 2 changed files with 17 additions and 2 deletions.
diff --git a/Analysis/TracedHeap.cs b/Analysis/TracedHeap.cs
@@ -116,7 +116,16 @@ public TracedHeap(IRootSet rootSet, ILogger logger)
                     m_objectAddressToPostorderIndex[lookupEntryIndex].PostorderIndex = postorderIndex;
                     lookupEntryIndex++;
 
-                    m_numberOfLiveBytes += m_traceableHeap.GetObjectSize(m_native.From(address), typeIndex, committedOnly: true);
+                    int objectSize = m_traceableHeap.GetObjectSize(m_native.From(address), typeIndex, committedOnly: true);
+                    if (objectSize < 0)
+                    {
+                        // This indicates a memory corruption (array or string with invalid length field)
+                        LogWarning(m_traceableHeap.TypeSystem.QualifiedName(typeIndex), $"object {postorderIndex} has negative size {objectSize}");
+                    }
+                    else
+                    {
+                        m_numberOfLiveBytes += objectSize;
+                    }
                 }
             }
             Array.Sort(m_objectAddressToPostorderIndex, (x, y) => x.Address.CompareTo(y.Address));

diff --git a/CommandInfrastructure/Command.cs b/CommandInfrastructure/Command.cs
@@ -547,7 +547,13 @@ protected void DumpObjectMemory(MemoryView objectView, int typeIndex, int indent
             int length = maxLength < stringLength ? maxLength : stringLength;
             for (int i = 0; i < length; i++)
             {
-                objectView.Read(CurrentTraceableHeap.TypeSystem.SystemStringFirstCharOffset + i * 2, out char c);
+                int offset = CurrentTraceableHeap.TypeSystem.SystemStringFirstCharOffset + i * 2;
+                if (offset + 2 > objectView.Size)
+                {
+                    // Guard against crashing if there is a memory corruption (string with invalid length)
+                    break;
+                }
+                objectView.Read(offset, out char c);
                 sb.Append(c);
             }