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Drop double-free logic in span_fuzz. #472

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Merged
copybara-service merged 1 commit into from
Aug 11, 2026
Merged

Drop double-free logic in span_fuzz. #472

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35 changes: 2 additions & 33 deletions tcmalloc/span_fuzz.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -12,8 +12,6 @@
// See the License for the specific language governing permissions and
// limitations under the License.

#include <setjmp.h>

#include <algorithm>
#include <cstddef>
#include <cstdint>
Expand All @@ -36,7 +34,6 @@
#include "tcmalloc/pages.h"
#include "tcmalloc/sizemap.h"
#include "tcmalloc/span.h"
#include "tcmalloc/testing/testutil.h"

namespace tcmalloc::tcmalloc_internal {
namespace {
Expand Down Expand Up @@ -80,15 +77,6 @@ struct Dealloc {
}
};

struct DeallocNoRemove {
uint8_t count;

template <typename Sink>
friend void AbslStringify(Sink& sink, const DeallocNoRemove& d) {
absl::Format(&sink, "DeallocNoRemove(%d)", d.count);
}
};

// Pushes objects into the Span using the ObjIdx interface.
struct DeallocIndex {
uint8_t count;
Expand All @@ -99,7 +87,6 @@ struct DeallocIndex {
}
};

// TODO(b/457842787): Include DeallocNoRemove in variant list.
using Instruction = std::variant<Alloc, Shuffle, Dealloc, DeallocIndex>;

void FuzzSpanInstructions(size_t object_size_direct, Length num_pages_direct,
Expand All @@ -114,11 +101,6 @@ void FuzzSpanInstructions(size_t object_size_direct, Length num_pages_direct,
std::vector<void*> batch;
std::mt19937 rng;

LongJmpScope scope;
if (setjmp(scope.buf_)) {
return;
}

// Truncate ranges to better explore state space.
const size_t object_size =
std::max(sizeof(void*), (object_size_direct % kMaxSize) &
Expand Down Expand Up @@ -146,7 +128,6 @@ void FuzzSpanInstructions(size_t object_size_direct, Length num_pages_direct,

live_ptrs.reserve(objects_per_span);
batch.resize(kMaxObjectsToMove);
bool did_double_free = false;

for (const auto& instruction : instructions) {
std::visit(
Expand All @@ -168,8 +149,7 @@ void FuzzSpanInstructions(size_t object_size_direct, Length num_pages_direct,
} else if constexpr (std::is_same_v<T, Shuffle>) {
std::shuffle(live_ptrs.begin(), live_ptrs.end(), rng);
} else if constexpr (std::is_same_v<T, Dealloc> ||
std::is_same_v<T, DeallocIndex> ||
std::is_same_v<T, DeallocNoRemove>) {
std::is_same_v<T, DeallocIndex>) {
size_t n = std::min<size_t>(arg.count, num_to_move);
n = std::min(n, live_ptrs.size());
if (n == 0) {
Expand Down Expand Up @@ -200,14 +180,7 @@ void FuzzSpanInstructions(size_t object_size_direct, Length num_pages_direct,
(void)span->FreelistPushBatch(ptrs, object_size, size_reciprocal);
}

if constexpr (!std::is_same_v<T, DeallocNoRemove>) {
live_ptrs.resize(live_ptrs.size() - n);
} else {
// double free: don't remove from live_ptrs
did_double_free = true;

// TODO(b/457842787): Detect the double free immediately.
}
live_ptrs.resize(live_ptrs.size() - n);
}
},
instruction);
Expand All @@ -223,10 +196,6 @@ void FuzzSpanInstructions(size_t object_size_direct, Length num_pages_direct,
}

free(mem);

// We expect to have crashed when draining `live_ptrs` if there was a double
// free.
EXPECT_FALSE(did_double_free);
}

FUZZ_TEST(SpanTest, FuzzSpanInstructions)
Expand Down
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