@matheusbsbs / matheus-bagliano / commits / 2dd804cd12

t5318: demonstrate commit-graph generation v2 corruption

When upgrading a commit-graph using generation v1 to one using generation v2, it is possible to force Git into a corrupt state where it (incorrectly) believes that a GDO2 chunk is necessary, *after* deciding not to write one. This makes subsequent reads using the commit-graph produce the following error message: fatal: commit-graph requires overflow generation data but has none Demonstrate this bug by increasing our test coverage to include a minimal example of upgrading a commit-graph from generation v1 to v2. The only notable components of this test are: - The committer date of the commit is chosen carefully so that the offset underflows when computed using a v1 generation number, but would not overflow when using v2 generation numbers. - The upgrade to generation number v2 must read in the v1 generation numbers, which we can do by passing `--changed-paths`, which will force the commit-graph internals to call `fill_commit_graph_info()`. A future patch will squash this bug. Reported-by: Jeff King <peff@peff.net> Reproduced-by: Will Chandler <wfc@wfchandler.org> Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Taylor Blau committed Jul 12, 2022 at 19:10 UTC 2dd804cd12143741ea4188346fba250e821609b5

1 file changed +27

t/t5318-commit-graph.sh

+27

index fbf0d64578..b85d07f60a 100755 --- a/t/t5318-commit-graph.sh +++ b/t/t5318-commit-graph.sh @@ -811,4 +811,31 @@ test_expect_success 'set up and verify repo with generation data overflow chunk' graph_git_behavior 'generation data overflow chunk repo' repo left right +test_expect_failure 'overflow during generation version upgrade' ' + git init overflow-v2-upgrade && + ( + cd overflow-v2-upgrade && + + # This commit will have a date at two seconds past the Epoch, + # and a (v1) generation number of 1, since it is a root commit. + # + # The offset will then be computed as 1-2, which will underflow + # to 2^31, which is greater than the v2 offset small limit of + # 2^31-1. + # + # This is sufficient to need a large offset table for the v2 + # generation numbers. + test_commit --date "@2 +0000" base && + git repack -d && + + # Test that upgrading from generation v1 to v2 correctly + # produces the overflow table. + git -c commitGraph.generationVersion=1 commit-graph write && + git -c commitGraph.generationVersion=2 commit-graph write \ + --changed-paths && + + git rev-list --all + ) +' + test_done