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fix: add bounds checking before GetFieldT in reflection VerifyObject #9101

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fix: add bounds checking before GetFieldT in reflection VerifyObject #9101

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13 changes: 13 additions & 0 deletions src/reflection.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -240,6 +240,14 @@ static bool VerifyObject(flatbuffers::Verifier& v,
return false;
}
} else {
// Verify the field offset points within the buffer before
// dereferencing it via GetFieldT. Without this check, a malformed
// table with an out-of-bounds field offset causes GetFieldT to
// compute a pointer outside the buffer, leading to a heap-buffer-
// overflow in ReadScalar. See github.com/google/flatbuffers/issues/9040
if (!table->VerifyField<uoffset_t>(v, field_def->offset(),
sizeof(uoffset_t)))
return false;
if (!VerifyObject(v, schema, *child_obj,
flatbuffers::GetFieldT(*table, *field_def),
field_def->required())) {
Expand All @@ -252,6 +260,11 @@ static bool VerifyObject(flatbuffers::Verifier& v,
// get union type from the prev field
voffset_t utype_offset = field_def->offset() - sizeof(voffset_t);
auto utype = table->GetField<uint8_t>(utype_offset, 0);
// Verify the field offset before dereferencing via GetFieldT.
// See github.com/google/flatbuffers/issues/9040
if (!table->VerifyField<uoffset_t>(v, field_def->offset(),
sizeof(uoffset_t)))
return false;
auto uval = reinterpret_cast<const uint8_t*>(
flatbuffers::GetFieldT(*table, *field_def));
if (!VerifyUnion(v, schema, utype, uval, *field_def)) {
Expand Down