[PATCH v4 1/3] sparse-checkout: fix segfault on malformed patterns

From: Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>
Date: Dec 16, 2021, 16:13 UTC
Message-ID: <5353c541d9f72aa0a14cd2b02e5ddcc0b6a4dae1.1639671222.git.gitgitgadget@gmail.com>
In-Reply-To: <pull.1069.v4.git.1639671222.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 now invalid.

The fix here is to stop trying to remove from the hashset. In addition, we disable cone mode sparse-checkout because of the malformed data. This results in the pattern-matching working with a possibly-slower algorithm, but using the patterns as they are in the sparse-checkout file.

This also changes the behavior of commands such as 'git sparse-checkout list' because the output patterns will be the contents of the sparse-checkout file instead of the list of directories. This is an existing behavior for other types of bad patterns.

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                              |  4 +---
 t/t1091-sparse-checkout-builtin.sh | 21 +++++++++++++++++++++
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/dir.c b/dir.c
index 5aa6fbad0b7..7e72958d51d 100644
--- a/dir.c
+++ b/dir.c
@@ -819,9 +819,7 @@ 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);
+		goto clear_hashmaps;
 	}
 
 	return;
diff --git a/t/t1091-sparse-checkout-builtin.sh b/t/t1091-sparse-checkout-builtin.sh
index 272ba1b566b..3921ea80138 100755
--- a/t/t1091-sparse-checkout-builtin.sh
+++ b/t/t1091-sparse-checkout-builtin.sh
@@ -708,4 +708,25 @@ 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
+
+	# Listing the patterns will notice the duplicate pattern and
+	# emit a warning. It will list the patterns directly instead
+	# of using the cone-mode translation to a set of directories.
+	git -C repo sparse-checkout list >actual 2>err &&
+	test_cmp repo/.git/info/sparse-checkout actual &&
+	grep "warning: your sparse-checkout file may have issues: pattern .* is repeated" err &&
+	grep "warning: disabling cone pattern matching" err
+'
+
 test_done

-- 
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