From d063a77eec6db30643817a26b32e8c7032fd98e2 Mon Sep 17 00:00:00 2001 From: Elijah Newren Date: Fri, 12 Jun 2026 12:57:27 -0700 Subject: [PATCH] commit-graph: use timestamp_t for max parent generation accumulator compute_reachable_generation_numbers() computes each commit's generation as max(c->date, max(parent.generation)) + 1 by walking its parents and accumulating their generations into a local uint32_t max_gen = 0; while info->get_generation() returns timestamp_t and compute_generation_from_max() already takes its max_gen parameter as timestamp_t. For v1 (topological levels) the narrowing is harmless because GENERATION_NUMBER_V1_MAX is less than 2^30, but for v2 (corrected committer dates) it silently truncates any parent generation that does not fit in 32 bits, i.e. any parent whose committer timestamp is at or beyond 2106-02-07 UTC (>= 2^32). The truncated max then causes child commits to end up with a corrected committer date that matches the parent's instead of being at least 1 higher. The bad value gets written into the commit-graph and causes problems later, and can be noticed by running `git commit-graph verify`. Widen the accumulator to timestamp_t. This is solely an in-memory arithmetic fix with no on-disk format change: the on-disk format already encodes timestamp_t values and existing readers handle them unchanged. This merely allows the code to compute the correct value to write to disk. The narrowing was introduced in 80c928d947c2 (commit-graph: simplify compute_generation_numbers(), 2023-03-20), which rewired v2 to use the shared compute_reachable_generation_numbers() helper; the helper's local accumulator had been declared uint32_t in the immediately preceding 368d19b0b7fa (commit-graph: refactor compute_topological_levels(), 2023-03-20) when only v1 was using it, where it was harmless. Add a new test with a future-dated parent and a present-day child; without the above fix, `git commit-graph verify` reports the descendant's stored generation as below parent + 1. Signed-off-by: Elijah Newren --- 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 9abe62bd5a278a..4b7156fd76596a 100644 --- a/commit-graph.c +++ b/commit-graph.c @@ -1669,7 +1669,7 @@ static void compute_reachable_generation_numbers( struct commit *current = list->item; struct commit_list *parent; int all_parents_computed = 1; - uint32_t max_gen = 0; + timestamp_t max_gen = 0; for (parent = current->parents; parent; parent = parent->next) { repo_parse_commit(info->r, parent->item); diff --git a/t/t5328-commit-graph-64bit-time.sh b/t/t5328-commit-graph-64bit-time.sh index d8891e6a922463..bc651b69deeea4 100755 --- a/t/t5328-commit-graph-64bit-time.sh +++ b/t/t5328-commit-graph-64bit-time.sh @@ -74,6 +74,15 @@ test_expect_success 'single commit with generation data exceeding UINT32_MAX' ' git -C repo-uint32-max commit-graph verify ' +test_expect_success 'descendant of commit with date exceeding UINT32_MAX' ' + git init repo-uint32-max-descendant && + test_commit -C repo-uint32-max-descendant \ + --date "@4294967300 +0000" future-parent && + test_commit -C repo-uint32-max-descendant present-day-child && + git -C repo-uint32-max-descendant commit-graph write --reachable && + git -C repo-uint32-max-descendant commit-graph verify +' + test_expect_success PERL_TEST_HELPERS 'reader notices out-of-bounds generation overflow' ' graph=.git/objects/info/commit-graph && test_when_finished "rm -rf $graph" &&