[PATCH v4] rerere: fix crashes due to unmatched opening conflict markers

["Marcel Röthke" <marcel@roethke.info>]

When rerere handles a conflict with an unmatched opening conflict marker
in a file with other conflicts, it will fail create a preimage and also
fail allocate the status member of struct rerere_dir. Currently the
status member is allocated after the error handling. This will lead to a
SEGFAULT when the status member is accessed during cleanup of the failed
parse.

Additionally, in subsequent executions of rerere, after removing the
MERGE_RR.lock manually, rerere crashes for a similar reason. MERGE_RR
points to a conflict id that has no preimage, therefore the status
member is not allocated and a SEGFAULT happens when trying to check if a
preimage exists.

Solve this by making sure the status field is allocated correctly and add
tests to prevent the bug from reoccurring.

This does not fix the root cause, failing to parse stray conflict
markers, but I don't think we can do much better than recognizing it,
printing an error, and moving on gracefully.

Signed-off-by: Marcel Röthke <marcel@roethke.info>
---
Interdiff against v3:
  diff --git a/t/t4200-rerere.sh b/t/t4200-rerere.sh
  index 1e80f76860..b0a3e84984 100755
  --- a/t/t4200-rerere.sh
  +++ b/t/t4200-rerere.sh
  @@ -731,7 +731,7 @@ test_expect_success 'rerere does not crash with unmatched conflict marker' '
   	bar
   	EOF
   	git add test &&
  -	git rebase --continue
  +	test_must_fail git rebase --continue
   '

   test_done

 rerere.c          |  5 ++++
 t/t4200-rerere.sh | 63 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+)

diff --git a/rerere.c b/rerere.c
index ca7e77ba68..4683d6cbb1 100644
--- a/rerere.c
+++ b/rerere.c
@@ -219,6 +219,11 @@ static void read_rr(struct repository *r, struct string_list *rr)
 		buf.buf[hexsz] = '\0';
 		id = new_rerere_id_hex(buf.buf);
 		id->variant = variant;
+		/*
+		 * make sure id->collection->status has enough space
+		 * for the variant we are interested in
+		 */
+		fit_variant(id->collection, variant);
 		string_list_insert(rr, path)->util = id;
 	}
 	strbuf_release(&buf);
diff --git a/t/t4200-rerere.sh b/t/t4200-rerere.sh
index fb53dddf79..b0a3e84984 100755
--- a/t/t4200-rerere.sh
+++ b/t/t4200-rerere.sh
@@ -671,4 +671,67 @@ test_expect_success 'test simple stage 1 handling' '
 	)
 '

+test_expect_success 'rerere does not crash with missing preimage' '
+	git config rerere.enabled true &&
+
+	echo bar >test &&
+	git add test &&
+	git commit -m "one" &&
+	git branch rerere_no_crash &&
+
+	echo foo >>test &&
+	git add test &&
+	git commit -m "two" &&
+
+	git checkout rerere_no_crash &&
+	echo "bar" >>test &&
+	git add test &&
+	git commit -m "three" &&
+
+	test_must_fail git rebase main &&
+	rm .git/rr-cache/*/preimage &&
+	git rebase --abort
+'
+
+test_expect_success 'rerere does not crash with unmatched conflict marker' '
+	git config rerere.enabled true &&
+
+	echo bar >test &&
+	git add test &&
+	git commit -m "one" &&
+	git branch rerere_no_preimage &&
+
+	cat >test <<-EOF &&
+	test
+	bar
+	foobar
+	EOF
+	git add test &&
+	git commit -m "two" &&
+
+	git checkout rerere_no_preimage &&
+	echo "bar" >>test &&
+	git add test &&
+	git commit -m "three" &&
+
+	cat >test <<-EOF &&
+	foobar
+	bar
+	bar
+	EOF
+	git add test &&
+	git commit -m "four" &&
+
+	test_must_fail git rebase main &&
+	cat >test <<-EOF &&
+	test
+	bar
+	<<<<<<< HEAD
+	foobar
+	bar
+	EOF
+	git add test &&
+	test_must_fail git rebase --continue
+'
+
 test_done
--
2.44.0