[PATCH] commit-graph: fix truncated generation numbers
- From
Patrick Steinhardt <ps@pks.im>
- Date
- Mar 27, 2023, 08:08 UTC
- Message-ID
- <f8a0a869e8b0882f05cac49d78f49ba3553d3c44.1679904401.git.ps@pks.im>
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@pks.im> ---
This commit applies on top of cbfe360b14 (commit-reach: add tips_reachable_from_bases(), 2023-03-20), which has recently been merged to next.
commit-graph.c | 2 +- t/t5328-commit-graph-64bit-time.sh | 9 +++++++++ 2 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/commit-graph.c b/commit-graph.c index 172e679db1..b96509354e 100644 --- a/commit-graph.c +++ b/commit-graph.c @@ -1565,7 +1565,7 @@ static timestamp_t get_generation_from_graph_data(struct commit *c, void *data) static void set_generation_v2(struct commit *c, timestamp_t t, void *data) { struct commit_graph_data *g = commit_graph_data_at(c); - g->generation = (uint32_t)t; + g->generation = t; } static void compute_generation_numbers(struct write_commit_graph_context *ctx) diff --git a/t/t5328-commit-graph-64bit-time.sh b/t/t5328-commit-graph-64bit-time.sh index 093f0c067a..57e4d9c699 100755 --- a/t/t5328-commit-graph-64bit-time.sh +++ b/t/t5328-commit-graph-64bit-time.sh @@ -63,4 +63,13 @@ test_expect_success 'set up and verify repo with generation data overflow chunk' graph_git_behavior 'overflow 2' repo left right +test_expect_success 'single commit with generation data exceeding UINT32_MAX' ' + git init repo-uint32-max && + cd repo-uint32-max && + test_commit --date "@4294967297 +0000" 1 && + git commit-graph write --reachable && + graph_read_expect 1 "generation_data" && + git commit-graph verify +' + test_done
-- 2.40.0