Skip to content

libutil: Add overflow check to alignUp #15149

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
xokdvium merged 1 commit into from
Feb 5, 2026
+35 −2
Merged

libutil: Add overflow check to alignUp #15149

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
28 changes: 28 additions & 0 deletions src/libutil-tests/alignment.cc
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -15,4 +15,32 @@ TEST(alignUp, notAPowerOf2)
ASSERT_DEATH({ alignUp(1u, 42); }, "alignment must be a power of 2");
}

template<typename T>
class alignUpOverflowTest : public ::testing::Test
{};

using UnsignedTypes = ::testing::Types<uint8_t, uint16_t, uint32_t, uint64_t>;
TYPED_TEST_SUITE(alignUpOverflowTest, UnsignedTypes);

TYPED_TEST(alignUpOverflowTest, lastSafeValue)
{
constexpr auto max = std::numeric_limits<TypeParam>::max();
ASSERT_EQ(alignUp<TypeParam>(max - 15, 16), (max - 15) & ~TypeParam{15});
ASSERT_NO_THROW(alignUp<TypeParam>(max - 15, 16));
}

TYPED_TEST(alignUpOverflowTest, overflowThrows)
{
constexpr auto max = std::numeric_limits<TypeParam>::max();
ASSERT_THROW(alignUp<TypeParam>(max - 14, 16), Error);
ASSERT_THROW(alignUp<TypeParam>(max, 16), Error);
ASSERT_THROW(alignUp<TypeParam>(max, 2), Error);
}

TYPED_TEST(alignUpOverflowTest, alignmentOneNeverOverflows)
{
constexpr auto max = std::numeric_limits<TypeParam>::max();
ASSERT_EQ(alignUp<TypeParam>(max, 1), max);
}

} // namespace nix
9 changes: 7 additions & 2 deletions src/libutil/include/nix/util/alignment.hh
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,9 +1,11 @@
#pragma once
///@file

#include "nix/util/error.hh"

#include <cassert>
#include <limits>
#include <type_traits>
#include <cstdint>
#include <bit>

namespace nix {
Expand All @@ -16,7 +18,10 @@ template<typename T>
constexpr T alignUp(T val, unsigned alignment)
{
assert(std::has_single_bit(alignment) && "alignment must be a power of 2");
T mask = ~(T{alignment} - 1u);
assert(alignment <= std::numeric_limits<T>::max());
T mask = ~(static_cast<T>(alignment) - 1u);
if (val > std::numeric_limits<T>::max() - (alignment - 1)) /* Overflow check. */
throw Error("can't align %d to %d: value is too large", val, alignment);
return (val + alignment - 1) & mask;
}

Expand Down
Loading