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GH-54936: [C++] Ensure reading an invalid map array from IPC doesn't crash #54939

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GH-54936: [C++] Ensure reading an invalid map array from IPC doesn't crash #54939

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16 changes: 16 additions & 0 deletions cpp/src/arrow/ipc/reader.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,7 @@
#include <flatbuffers/flatbuffers.h> // IWYU pragma: export

#include "arrow/array.h"
#include "arrow/array/validate.h"
#include "arrow/buffer.h"
#include "arrow/extension_type.h"
#include "arrow/io/caching.h"
Expand Down Expand Up @@ -455,6 +456,21 @@ class ArrayLoader {

Status Visit(const MapType& type) {
RETURN_NOT_OK(LoadList(type));
if (!out_->child_data.empty()) {

@taepper taepper Oct 27, 2026

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I think we can turn this into a

    DCHECK_EQ(out_->child_data.size(), 1);

after LoadList succeeds without an error

// Ensure that GetNullCount() calls in MapArray::ValidateChildData
// don't access invalid memory.
Comment on lines +460 to +461

@taepper taepper Oct 27, 2026

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This is because when null_count == -1, it will be inferred from the unvalidated data? Can we add a (non-fuzzing based) test for this directly?

// We cannot call array validation as it will fail on non-native endianness
// (due to checking the last offset on variable-width data) or missing
// dictionaries (they are not yet populated at this point).
const ArrayData& child_data = *out_->child_data[0];
if (child_data.null_count != 0) {
return Status::Invalid("Map array child array should have no nulls");
}
if (!child_data.child_data.empty() && child_data.child_data[0]->null_count != 0) {
return Status::Invalid("Map array keys array should have no nulls");
}
}
// If we don't do this, MapArray::SetData will abort on invalid data.
return MapArray::ValidateChildData(out_->child_data);
}

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2 changes: 1 addition & 1 deletion testing
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Submodule testing updated 1 files
+ − data/arrow-ipc-file/clusterfuzz-testcase-arrow-ipc-file-fuzz-5335203313418240
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