From d3af1c193d4d62668a9d7ea98e2ef3771ac4e65a Mon Sep 17 00:00:00 2001 From: Patrick Steinhardt Date: Mon, 27 Mar 2023 10:08:25 +0200 Subject: [PATCH] commit-graph: fix truncated generation numbers 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 Signed-off-by: Junio C Hamano --- 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