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Fix UB in const_fixed_iterator with negative offsets #164

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Merged
joto merged 1 commit into from
Oct 15, 2026
Merged

Fix UB in const_fixed_iterator with negative offsets #164

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10 changes: 5 additions & 5 deletions include/protozero/iterators.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -243,30 +243,30 @@ class const_fixed_iterator {
}

const_fixed_iterator& operator+=(difference_type val) noexcept {
m_data += (sizeof(value_type) * val);
m_data += (static_cast<difference_type>(sizeof(value_type)) * val);
return *this;
}

friend const_fixed_iterator operator+(const_fixed_iterator lhs, difference_type rhs) noexcept {
const_fixed_iterator tmp{lhs};
tmp.m_data += (sizeof(value_type) * rhs);
tmp.m_data += (static_cast<difference_type>(sizeof(value_type)) * rhs);
return tmp;
}

friend const_fixed_iterator operator+(difference_type lhs, const_fixed_iterator rhs) noexcept {
const_fixed_iterator tmp{rhs};
tmp.m_data += (sizeof(value_type) * lhs);
tmp.m_data += (static_cast<difference_type>(sizeof(value_type)) * lhs);
return tmp;
}

const_fixed_iterator& operator-=(difference_type val) noexcept {
m_data -= (sizeof(value_type) * val);
m_data -= (static_cast<difference_type>(sizeof(value_type)) * val);
return *this;
}

friend const_fixed_iterator operator-(const_fixed_iterator lhs, difference_type rhs) noexcept {
const_fixed_iterator tmp{lhs};
tmp.m_data -= (sizeof(value_type) * rhs);
tmp.m_data -= (static_cast<difference_type>(sizeof(value_type)) * rhs);
return tmp;
}

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28 changes: 28 additions & 0 deletions test/unit/test_iterators.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -40,3 +40,31 @@ TEST_CASE("get_packed varint rejects a truncated trailing varint") {
REQUIRE_THROWS_AS(item.get_packed_uint64(), protozero::end_of_buffer_exception);
}


TEST_CASE("fixed_iterator supports negative offsets") {
// field 1, wire type 2; length 12; fixed32 values 1, 2 and 3.
const std::string buffer{"\x0a\x0c\x01\x00\x00\x00\x02\x00\x00\x00\x03\x00\x00\x00", 14};
protozero::pbf_reader item{buffer};

REQUIRE(item.next());
const auto range = item.get_packed_fixed32();
const auto end = range.end();

REQUIRE(*std::prev(end) == 3);
REQUIRE(end[-1] == 3);
REQUIRE(end[-3] == 1);
REQUIRE(*(end + -2) == 2);
REQUIRE(*(-2 + end) == 2);
REQUIRE(*(end - 2) == 2);
REQUIRE(*(range.begin() - -1) == 2);

auto it = end;
it += -1;
REQUIRE(*it == 3);
it -= 1;
REQUIRE(*it == 2);
it -= -1;
REQUIRE(*it == 3);
REQUIRE(it - end == -1);
REQUIRE(range.begin() - end == -3);
}
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