[scudo] Update error handling for seondary cache entry count (#95595)

Initially, the scudo allocator would return an error if the user
attempted to set the cache capacity
(i.e. the number of possible entries in the cache) above the maximum
cache capacity.
Now the allocator will resort to using the maximum cache capacity in
this event.
An error will still be returned if the user attempts to set the number
of entries to a negative value.

Author: JoshuaMBa

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

@@ -391,10 +391,11 @@ template <typename Config> class MapAllocatorCache {
       return true;
     }
     if (O == Option::MaxCacheEntriesCount) {
-      const u32 MaxCount = static_cast<u32>(Value);
-      if (MaxCount > Config::getEntriesArraySize())
+      if (Value < 0)
         return false;
-      atomic_store_relaxed(&MaxEntriesCount, MaxCount);
+      atomic_store_relaxed(
+          &MaxEntriesCount,
+          Min<u32>(static_cast<u32>(Value), Config::getEntriesArraySize()));
       return true;
     }
     if (O == Option::MaxCacheEntrySize) {

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

@@ -192,9 +192,9 @@ TEST_F(MapAllocatorTest, SecondaryIterate) {
 
 TEST_F(MapAllocatorTest, SecondaryOptions) {
   // Attempt to set a maximum number of entries higher than the array size.
-  EXPECT_FALSE(
-      Allocator->setOption(scudo::Option::MaxCacheEntriesCount, 4096U));
-  // A negative number will be cast to a scudo::u32, and fail.
+  EXPECT_TRUE(Allocator->setOption(scudo::Option::MaxCacheEntriesCount, 4096U));
+
+  // Attempt to set an invalid (negative) number of entries
   EXPECT_FALSE(Allocator->setOption(scudo::Option::MaxCacheEntriesCount, -1));
   if (Allocator->canCache(0U)) {
     // Various valid combinations.