[PATCH 13/24] bundle-uri: limit recursion depth for bundle lists

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

From: Derrick Stolee <derrickstolee@github.com>

The next change will start allowing us to parse bundle lists that are
downloaded from a provided bundle URI. Those lists might point to other
lists, which could proceed to an arbitrary depth (and even create
cycles). Restructure fetch_bundle_uri() to have an internal version that
has a recursion depth. Compare that to a new max_bundle_uri_depth
constant that is twice as high as we expect this depth to be for any
legitimate use of bundle list linking.

We can consider making max_bundle_uri_depth a configurable value if
there is demonstrated value in the future.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 bundle-uri.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/bundle-uri.c b/bundle-uri.c
index ff215422888..74a26ce6c00 100644
--- a/bundle-uri.c
+++ b/bundle-uri.c
@@ -308,11 +308,25 @@ static int unbundle_from_file(struct repository *r, const char *file)
 	return result;
 }
 
-int fetch_bundle_uri(struct repository *r, const char *uri)
+/**
+ * This limits the recursion on fetch_bundle_uri_internal() when following
+ * bundle lists.
+ */
+static int max_bundle_uri_depth = 4;
+
+static int fetch_bundle_uri_internal(struct repository *r,
+				     const char *uri,
+				     int depth)
 {
 	int result = 0;
 	struct strbuf filename = STRBUF_INIT;
 
+	if (depth >= max_bundle_uri_depth) {
+		warning(_("exceeded bundle URI recursion limit (%d)"),
+			max_bundle_uri_depth);
+		return -1;
+	}
+
 	find_temp_filename(&filename);
 	if ((result = copy_uri_to_file(uri, filename.buf)))
 		goto cleanup;
@@ -335,6 +349,11 @@ cleanup:
 	return result;
 }
 
+int fetch_bundle_uri(struct repository *r, const char *uri)
+{
+	return fetch_bundle_uri_internal(r, uri, 0);
+}
+
 /**
  * General API for {transport,connect}.c etc.
  */
-- 
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