Subject: [PATCHv2 2/2] rerere: avoid buffer overrun

From: Elijah Newren <[email-masked]>
Date: Tue, 11 Sep 2018 11:55:46 -0700

check_one_conflict() compares `i` to `active_nr` in two places to avoid
buffer overruns, but left out an important third location.

The code did used to have a check here comparing i to active_nr, back
before commit fb70a06da2f1 ("rerere: fix an off-by-one non-bug",
2015-06-28), however the code at the time used an 'if' rather than a
'while' meaning back then that this loop could not have read past the
end of the array, making the check unnecessary and it was removed.
Unfortunately, in commit 5eda906b2873 ("rerere: handle conflicts with
multiple stage #1 entries", 2015-07-24), the 'if' was changed to a
'while' and the check comparing i and active_nr was not re-instated,
leading to this problem.

Signed-off-by: Elijah Newren <[email-masked]>
---
 rerere.c          | 2 +-
 t/t4200-rerere.sh | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/rerere.c b/rerere.c
index c7787aa07f..783d4dae2a 100644
--- a/rerere.c
+++ b/rerere.c
@@ -533,7 +533,7 @@ static int check_one_conflict(int i, int *type)
 	}
 
 	*type = PUNTED;
-	while (ce_stage(active_cache[i]) == 1)
+	while (i < active_nr && ce_stage(active_cache[i]) == 1)
 		i++;
 
 	/* Only handle regular files with both stages #2 and #3 */
diff --git a/t/t4200-rerere.sh b/t/t4200-rerere.sh
index f9294b7677..313222d0d6 100755
--- a/t/t4200-rerere.sh
+++ b/t/t4200-rerere.sh
@@ -596,7 +596,7 @@ test_expect_success 'setup simple stage 1 handling' '
 	)
 '
 
-test_expect_failure 'test simple stage 1 handling' '
+test_expect_success 'test simple stage 1 handling' '
 	(
 		cd stage_1_handling &&
 
-- 
2.19.0.2.gdbd064c81f