t/t5318: introduce failing 'git commit-graph write' tests

When invoking 'git commit-graph' in a corrupt repository, one can cause
a segfault when ancestral commits are corrupt in one way or another.
This is due to two function calls in the 'commit-graph.c' code that may
return NULL, but are not checked for NULL-ness before dereferencing.

Before fixing the bug, introduce two failing tests that demonstrate the
problem. The first test corrupts an ancestral commit's parent to point
to a non-existent object. The second test instead corrupts an ancestral
tree by removing the 'tree' information entirely from the commit. Both
of these cases cause segfaults, each at different lines.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Acked-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index ab3eccf0fafa3f8e9158b6347a544a8b4202b7ce..c855f819302dc991853244ee65a053b92eee964e 100755 (executable)
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -585,4 +585,47 @@ test_expect_success 'get_commit_tree_in_graph works for non-the_repository' '
        test_cmp expect actual
 '
 
+test_expect_failure 'corrupt commit-graph write (broken parent)' '
+       rm -rf repo &&
+       git init repo &&
+       (
+               cd repo &&
+               empty="$(git mktree </dev/null)" &&
+               cat >broken <<-EOF &&
+               tree $empty
+               parent 0000000000000000000000000000000000000000
+               author whatever <whatever@example.com> 1234 -0000
+               committer whatever <whatever@example.com> 1234 -0000
+
+               broken commit
+               EOF
+               broken="$(git hash-object -w -t commit --literally broken)" &&
+               git commit-tree -p "$broken" -m "good commit" "$empty" >good &&
+               test_must_fail git commit-graph write --stdin-commits \
+                       <good 2>test_err &&
+               test_i18ngrep "unable to parse commit" test_err
+       )
+'
+
+test_expect_failure 'corrupt commit-graph write (missing tree)' '
+       rm -rf repo &&
+       git init repo &&
+       (
+               cd repo &&
+               tree="$(git mktree </dev/null)" &&
+               cat >broken <<-EOF &&
+               parent 0000000000000000000000000000000000000000
+               author whatever <whatever@example.com> 1234 -0000
+               committer whatever <whatever@example.com> 1234 -0000
+
+               broken commit
+               EOF
+               broken="$(git hash-object -w -t commit --literally broken)" &&
+               git commit-tree -p "$broken" -m "good" "$tree" >good &&
+               test_must_fail git commit-graph write --stdin-commits \
+                       <good 2>test_err &&
+               test_i18ngrep "unable to get tree for" test_err
+       )
+'
+
 test_done