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security: fix integer overflow and OOB writes in reflection.cpp #9065

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security: fix integer overflow and OOB writes in reflection.cpp #9065

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5e1b9a0
security: fix integer overflow and OOB writes in reflection.cpp
sharadboni Apr 27, 2026
c4b119e
Fix integer overflow in IndirectHelper::Read offset calculation
sharadboni Apr 28, 2026
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6 changes: 4 additions & 2 deletions include/flatbuffers/buffer.h
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Original file line number Diff line number Diff line change
Expand Up @@ -130,7 +130,8 @@ struct IndirectHelper<OffsetT<T>> {
static return_type Read(const uint8_t* const p, const offset_type i) {
// Offsets are relative to themselves, so first update the pointer to
// point to the offset location.
const uint8_t* const offset_location = p + i * element_stride;
const uint8_t* const offset_location =
p + static_cast<uint64_t>(i) * element_stride;

// Then read the scalar value of the offset (which may be 32 or 64-bits) and
// then determine the relative location from the offset location.
Expand All @@ -140,7 +141,8 @@ struct IndirectHelper<OffsetT<T>> {
static mutable_return_type Read(uint8_t* const p, const offset_type i) {
// Offsets are relative to themselves, so first update the pointer to
// point to the offset location.
uint8_t* const offset_location = p + i * element_stride;
uint8_t* const offset_location =
p + static_cast<uint64_t>(i) * element_stride;

// Then read the scalar value of the offset (which may be 32 or 64-bits) and
// then determine the relative location from the offset location.
Expand Down
21 changes: 15 additions & 6 deletions src/reflection.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,8 @@

#include "flatbuffers/reflection.h"

#include <climits>

#include "flatbuffers/util.h"

// Helper functionality for reflection.
Expand Down Expand Up @@ -384,7 +386,9 @@ void ForAllFields(const reflection::Object* object, bool reverse,
// Create the mapping of field ID to the index into the vector.
for (uint32_t i = 0; i < object->fields()->size(); ++i) {
auto field = object->fields()->Get(i);
field_to_id_map[field->id()] = i;
if (field->id() < field_to_id_map.size()) {
field_to_id_map[field->id()] = i;
}
}

for (size_t i = 0; i < field_to_id_map.size(); ++i) {
Expand Down Expand Up @@ -598,7 +602,9 @@ void SetString(const reflection::Schema& schema, const std::string& val,
auto start = str_start + static_cast<uoffset_t>(sizeof(uoffset_t));
if (delta) {
// Clear the old string, since we don't want parts of it remaining.
memset(flatbuf->data() + start, 0, str->size());
if (start + str->size() <= flatbuf->size()) {
memset(flatbuf->data() + start, 0, str->size());
}
// Different size, we must expand (or contract).
ResizeContext ctx(schema, start, delta, flatbuf, root_table);
// Set the new length.
Expand All @@ -613,8 +619,10 @@ uint8_t* ResizeAnyVector(const reflection::Schema& schema, uoffset_t newsize,
const VectorOfAny* vec, uoffset_t num_elems,
uoffset_t elem_size, std::vector<uint8_t>* flatbuf,
const reflection::Object* root_table) {
auto delta_elem = static_cast<int>(newsize) - static_cast<int>(num_elems);
auto delta_bytes = delta_elem * static_cast<int>(elem_size);
auto delta_elem =
static_cast<int64_t>(newsize) - static_cast<int64_t>(num_elems);
auto delta_bytes = delta_elem * static_cast<int64_t>(elem_size);
if (delta_bytes < INT_MIN || delta_bytes > INT_MAX) { return nullptr; }
auto vec_start = reinterpret_cast<const uint8_t*>(vec) - flatbuf->data();
auto start = static_cast<uoffset_t>(vec_start) +
static_cast<uoffset_t>(sizeof(uoffset_t)) +
Expand All @@ -623,10 +631,11 @@ uint8_t* ResizeAnyVector(const reflection::Schema& schema, uoffset_t newsize,
if (delta_elem < 0) {
// Clear elements we're throwing away, since some might remain in the
// buffer.
auto size_clear = -delta_elem * elem_size;
auto size_clear = static_cast<size_t>(-delta_elem) * elem_size;
memset(flatbuf->data() + start - size_clear, 0, size_clear);
}
ResizeContext ctx(schema, start, delta_bytes, flatbuf, root_table);
ResizeContext ctx(schema, start, static_cast<int>(delta_bytes), flatbuf,
root_table);
WriteScalar(flatbuf->data() + vec_start, newsize); // Length field.
// Set new elements to 0.. this can be overwritten by the caller.
if (delta_elem > 0) {
Expand Down