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CDRIVER-5641: Fixes for packed_bit edge cases on systems with 32-bit size_t #1904

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Mar 11, 2025
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CDRIVER-5641: Fixes for packed_bit edge cases on systems with 32-bit size_t #1904

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6a8f4fc
CDRIVER-5641: Fix test_bson_vector_edge_cases_packed_bit assert on pl…
Mar 7, 2025
9f8ffa5
CDRIVER-5641: Fix bson_vector_packed_bit_binary_data_length on platfo…
Mar 7, 2025
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6 changes: 3 additions & 3 deletions src/libbson/src/bson/bson-vector.h
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Original file line number Diff line number Diff line change
Expand Up @@ -296,11 +296,11 @@ bson_vector_float32_binary_data_length (size_t element_count)
static BSON_INLINE uint32_t
bson_vector_packed_bit_binary_data_length (size_t element_count)
{
const size_t max_representable = (size_t) BSON_MIN (
(uint64_t) SIZE_MAX, ((uint64_t) UINT32_MAX - (uint64_t) BSON_VECTOR_HEADER_LEN) * (uint64_t) 8);
const size_t max_representable =
(size_t) BSON_MIN ((uint64_t) SIZE_MAX, ((uint64_t) UINT32_MAX - (uint64_t) BSON_VECTOR_HEADER_LEN) * 8u);
return element_count > max_representable
? 0u
: (uint32_t) ((element_count + (size_t) 7) / (size_t) 8) + (uint32_t) BSON_VECTOR_HEADER_LEN;
: (uint32_t) (((uint64_t) element_count + 7u) / 8u) + (uint32_t) BSON_VECTOR_HEADER_LEN;
}


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28 changes: 26 additions & 2 deletions src/libbson/tests/test-bson-vector.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1495,21 +1495,45 @@ test_bson_vector_edge_cases_float32 (void)
static void
test_bson_vector_edge_cases_packed_bit (void)
{
// Test UINT32_MAX as an element count. This is the largest representable on systems with a 32-bit size_t.
uint32_t len_for_max_count = (uint32_t) (((uint64_t) UINT32_MAX + 7u) / 8u + BSON_VECTOR_HEADER_LEN);
{
ASSERT_CMPUINT32 (bson_vector_packed_bit_binary_data_length ((size_t) UINT32_MAX), ==, len_for_max_count);
ASSERT_CMPUINT32 (bson_vector_packed_bit_binary_data_length ((size_t) UINT32_MAX - 1u), ==, len_for_max_count);
ASSERT_CMPUINT32 (bson_vector_packed_bit_binary_data_length ((size_t) UINT32_MAX - 6u), ==, len_for_max_count);
ASSERT_CMPUINT32 (
bson_vector_packed_bit_binary_data_length ((size_t) UINT32_MAX - 7u), ==, len_for_max_count - 1u);
ASSERT_CMPUINT32 (
bson_vector_packed_bit_binary_data_length ((size_t) UINT32_MAX - 8u), ==, len_for_max_count - 1u);
}

// Test the real max_representable_elements only if size_t is large enough.
#if SIZE_MAX > UINT32_MAX
size_t max_representable_elements = ((size_t) UINT32_MAX - BSON_VECTOR_HEADER_LEN) * 8u;

// Test binary_data_length (uint32_t) edge cases, without any allocation.
{
ASSERT_CMPUINT32 (bson_vector_packed_bit_binary_data_length ((size_t) UINT32_MAX + 1u), ==, len_for_max_count);
ASSERT_CMPUINT32 (
bson_vector_packed_bit_binary_data_length ((size_t) UINT32_MAX + 2u), ==, len_for_max_count + 1u);
ASSERT_CMPUINT32 (
bson_vector_packed_bit_binary_data_length ((size_t) UINT32_MAX + 9u), ==, len_for_max_count + 1u);
ASSERT_CMPUINT32 (
bson_vector_packed_bit_binary_data_length (max_representable_elements - 8u), ==, UINT32_MAX - 1u);
ASSERT_CMPUINT32 (bson_vector_packed_bit_binary_data_length (max_representable_elements - 7u), ==, UINT32_MAX);
ASSERT_CMPUINT32 (bson_vector_packed_bit_binary_data_length (max_representable_elements), ==, UINT32_MAX);
ASSERT_CMPUINT32 (bson_vector_packed_bit_binary_data_length (max_representable_elements + 1u), ==, 0);
}
#endif // SIZE_MAX > UINT32_MAX

// Needs little real memory because most bytes are never accessed,
// but we should require a virtual address space larger than 32 bits.
// If we additionally have a 64-bit address space, allocate this max-sized vector and run tests.
// Needs little real memory because most bytes are never accessed.
#if BSON_WORD_SIZE > 32

#if !(SIZE_MAX > UINT32_MAX)
#error 64-bit platforms should have a 64-bit size_t
#endif

size_t expected_bson_overhead =
5 /* empty bson document */ + 3 /* "v" element header */ + 5 /* binary item header */;
size_t max_alloc_bytes = (size_t) BSON_MAX_SIZE - expected_bson_overhead - BSON_VECTOR_HEADER_LEN;
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