[PATCH v2 1/4] sparse-checkout: fix segfault on malformed patterns

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <dstolee@microsoft.com>

Then core.sparseCheckoutCone is enabled, the sparse-checkout patterns are
used to populate two hashsets that accelerate pattern matching. If the user
modifies the sparse-checkout file outside of the 'sparse-checkout' builtin,
then strange patterns can happen, triggering some error checks.

One of these error checks is possible to hit when some special characters
exist in a line. A warning message is correctly written to stderr, but then
there is additional logic that attempts to remove the line from the hashset
and free the data. This leads to a segfault in the 'git sparse-checkout
list' command because it iterates over the contents of the hashset, which is
no invalid.

The fix here is to stop trying to remove from the hashset. Better to leave
bad data in the sparse-checkout matching logic (with a warning) than to
segfault. If we are in this state, then we are already traversing into
undefined behavior, so this change to keep the entry in the hashset is no
worse than removing it.

Add a test that triggers the segfault without the code change.

Reported-by: John Burnett <johnburnett@johnburnett.com>
Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 dir.c                              |  3 ---
 t/t1091-sparse-checkout-builtin.sh | 15 +++++++++++++++
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/dir.c b/dir.c
index 5aa6fbad0b7..0693c7cb3ee 100644
--- a/dir.c
+++ b/dir.c
@@ -819,9 +819,6 @@ static void add_pattern_to_hashsets(struct pattern_list *pl, struct path_pattern
 		/* we already included this at the parent level */
 		warning(_("your sparse-checkout file may have issues: pattern '%s' is repeated"),
 			given->pattern);
-		hashmap_remove(&pl->parent_hashmap, &translated->ent, &data);
-		free(data);
-		free(translated);
 	}
 
 	return;
diff --git a/t/t1091-sparse-checkout-builtin.sh b/t/t1091-sparse-checkout-builtin.sh
index 272ba1b566b..c72b8ee2e7b 100755
--- a/t/t1091-sparse-checkout-builtin.sh
+++ b/t/t1091-sparse-checkout-builtin.sh
@@ -708,4 +708,19 @@ test_expect_success 'cone mode clears ignored subdirectories' '
 	test_cmp expect out
 '
 
+test_expect_success 'malformed cone-mode patterns' '
+	git -C repo sparse-checkout init --cone &&
+	mkdir -p repo/foo/bar &&
+	touch repo/foo/bar/x repo/foo/y &&
+	cat >repo/.git/info/sparse-checkout <<-\EOF &&
+	/*
+	!/*/
+	/foo/
+	!/foo/*/
+	/foo/\*/
+	EOF
+	cat repo/.git/info/sparse-checkout &&
+	git -C repo sparse-checkout list
+'
+
 test_done
-- 
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