Patrick Steinhardt <ps@xxxxxx> writes: > In 80c928d947 (commit-graph: simplify compute_generation_numbers(), > 2023-03-20), the code to compute generation numbers was simplified to > use the same infrastructure as is used to compute topological levels. > This refactoring introduced a bug where the generation numbers are > truncated when they exceed UINT32_MAX because we explicitly cast the > computed generation number to `uint32_t`. This is not required though: > both the computed value and the field of `struct commit_graph_data` are > of the same type `timestamp_t` already, so casting to `uint32_t` will > cause truncation. > > This cast can cause us to miscompute generation data overflows: > > 1. Given a commit with no parents and committer date > `UINT32_MAX + 1`. > > 2. We compute its generation number as `UINT32_MAX + 1`, but > truncate it to `1`. > > 3. We calculate the generation offset via `$generation - $date`, > which is thus `1 - (UINT32_MAX + 1)`. The computation underflows > and we thus end up with an offset that is bigger than the maximum > allowed offset. > > As a result, we'd be writing generation data overflow information into > the commit-graph that is bogus and ultimately not even required. > > Fix this bug by removing the needless cast. > > Signed-off-by: Patrick Steinhardt <ps@xxxxxx> > --- > > This commit applies on top of cbfe360b14 (commit-reach: add > tips_reachable_from_bases(), 2023-03-20), which has recently been merged > to next. The patch is clearly explained and the change looks quite straight-forward. Derrick, Ack? Thanks.
