[scudo] allocation_ring_buffer_size <= 0 disables buffer (#71791)

Prevent a null pointer exception for allocation_ring_buffer_size < 0.

Author: fmayer

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

@@ -886,7 +886,7 @@ class Allocator {
 
   void setTrackAllocationStacks(bool Track) {
     initThreadMaybe();
-    if (getFlags()->allocation_ring_buffer_size == 0) {
+    if (getFlags()->allocation_ring_buffer_size <= 0) {
       DCHECK(!Primary.Options.load().get(OptionBit::TrackAllocationStacks));
       return;
     }
@@ -1490,10 +1490,10 @@ class Allocator {
   }
 
   void mapAndInitializeRingBuffer() {
+    if (getFlags()->allocation_ring_buffer_size <= 0)
+      return;
     u32 AllocationRingBufferSize =
         static_cast<u32>(getFlags()->allocation_ring_buffer_size);
-    if (AllocationRingBufferSize < 1)
-      return;
     MemMapT MemMap;
     MemMap.map(
         /*Addr=*/0U,

compiler-rt/lib/scudo/standalone/flags.inc

@@ -47,4 +47,5 @@ SCUDO_FLAG(int, release_to_os_interval_ms, SCUDO_ANDROID ? INT32_MIN : 5000,
            "memory to the OS. Negative values disable the feature.")
 
 SCUDO_FLAG(int, allocation_ring_buffer_size, 32768,
-           "Entries to keep in the allocation ring buffer for scudo.")
+           "Entries to keep in the allocation ring buffer for scudo. "
+           "Values less or equal to zero disable the buffer.")