[compiler-rt] [scudo] do not store size inside ring buffer (PR #74541)

[Florian Mayer via llvm-commits]

================
@@ -1408,17 +1409,19 @@ class Allocator {
                                      size_t &NextErrorReport,
                                      uintptr_t FaultAddr,
                                      const StackDepot *Depot,
-                                     const char *RingBufferPtr) {
+                                     const char *RingBufferPtr,
+                                     size_t RingBufferSize) {
     auto *RingBuffer =
         reinterpret_cast<const AllocationRingBuffer *>(RingBufferPtr);
-    if (!RingBuffer || RingBuffer->Size == 0)
+    size_t RingBufferElements = ringBufferElementsFromBytes(RingBufferSize);
+    if (!RingBuffer || RingBufferElements == 0)
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fmayer wrote:

This function assumes arbitrary input (and is fuzzed with it), so I did it like this to be on the safe side. Checking on the caller makes less sense, because `RingBufferElements == 0` means `RingBufferSize < sizeof(AllocationRingBuffer) + sizeof(AllocationRingBuffer::Entry)`.

https://github.com/llvm/llvm-project/pull/74541