[PATCH v1] negotiator/default.c: avoid stack overflow

[Han Xin <hanxin.hx@bytedance.com>]

mark_common() in negotiator/default.c may overflow the stack due to
recursive function calls. Avoid this by instead recursing using a
heap-allocated data structure.

This is the same case as [1].

1. https://lore.kernel.org/git/20221025232934.1504445-1-jonathantanmy@google.com/

Reported-by: Xin Xing <xingxin.xx@bytedance.com>
Signed-off-by: Han Xin <hanxin.hx@bytedance.com>
---
 negotiator/default.c  | 16 ++++++++++++----
 negotiator/skipping.c |  2 ++
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/negotiator/default.c b/negotiator/default.c
index f4b78eb47d..6ab7f11409 100644
--- a/negotiator/default.c
+++ b/negotiator/default.c
@@ -55,9 +55,15 @@ static int clear_marks(const char *refname, const struct object_id *oid,
 static void mark_common(struct negotiation_state *ns, struct commit *commit,
 		int ancestors_only, int dont_parse)
 {
-	if (commit != NULL && !(commit->object.flags & COMMON)) {
+	struct prio_queue queue = { NULL };
+
+	prio_queue_put(&queue, commit);
+	while ((commit = prio_queue_get(&queue))) {
 		struct object *o = (struct object *)commit;
 
+		if (commit == NULL || (commit->object.flags & COMMON))
+			continue;
+
 		if (!ancestors_only)
 			o->flags |= COMMON;
 
@@ -70,15 +76,17 @@ static void mark_common(struct negotiation_state *ns, struct commit *commit,
 				ns->non_common_revs--;
 			if (!o->parsed && !dont_parse)
 				if (repo_parse_commit(the_repository, commit))
-					return;
+					continue;
 
+			ancestors_only = 0;
 			for (parents = commit->parents;
 					parents;
 					parents = parents->next)
-				mark_common(ns, parents->item, 0,
-					    dont_parse);
+				prio_queue_put(&queue, parents->item);
 		}
 	}
+
+	clear_prio_queue(&queue);
 }
 
 /*
diff --git a/negotiator/skipping.c b/negotiator/skipping.c
index c7d6ab39bc..3d262b3533 100644
--- a/negotiator/skipping.c
+++ b/negotiator/skipping.c
@@ -108,6 +108,8 @@ static void mark_common(struct data *data, struct commit *seen_commit)
 				prio_queue_put(&queue, p->item);
 		}
 	}
+
+	clear_prio_queue(&queue);
 }
 
 /*
-- 
2.40.0