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Fix handling of integer wraparound in megolm.c

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This commit is contained in:
Richard van der Hoff 2016-05-24 17:52:35 +01:00
parent 1f31427139
commit 01ea3d4b9a
2 changed files with 22 additions and 2 deletions
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8
src/megolm.c
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@ -108,8 +108,12 @@ void megolm_advance_to(Megolm *megolm, uint32_t advance_to) {
uint32_t mask = (~(uint32_t)0) << shift; uint32_t mask = (~(uint32_t)0) << shift;
int k; int k;
/* how many times to we need to rehash this part? */ /* how many times do we need to rehash this part?
int steps = (advance_to >> shift) - (megolm->counter >> shift); *
* '& 0xff' ensures we handle integer wraparound correctly
*/
unsigned int steps =
((advance_to >> shift) - (megolm->counter >> shift)) & 0xff;
if (steps == 0) { if (steps == 0) {
continue; continue;

16
tests/test_megolm.cpp
View file

@ -82,4 +82,20 @@ std::uint8_t random_bytes[] =
assert_equals(expected3, megolm_get_data(&mr), MEGOLM_RATCHET_LENGTH); assert_equals(expected3, megolm_get_data(&mr), MEGOLM_RATCHET_LENGTH);
} }
{
TestCase test_case("Megolm::advance wraparound");
Megolm mr1, mr2;
megolm_init(&mr1, random_bytes, 0xffffffffUL);
megolm_advance_to(&mr1, 0x1000000);
assert_equals(0x1000000U, mr1.counter);
megolm_init(&mr2, random_bytes, 0);
megolm_advance_to(&mr2, 0x2000000);
assert_equals(0x2000000U, mr2.counter);
assert_equals(megolm_get_data(&mr2), megolm_get_data(&mr1), MEGOLM_RATCHET_LENGTH);
}
} }