Subject: [PATCH] Segmentation fault on non-commit objects.

From: Davide Berardi <[email-masked]>
Date: Tue, 29 Oct 2019 10:27:35 +0100

Fixed segmentation fault that can be triggered using
$ git clone --branch $object $repository
with object pointing to a non-commit (e.g. a blob).

Signed-off-by: Davide Berardi <[email-masked]>
---
 builtin/clone.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/builtin/clone.c b/builtin/clone.c
index f665b28ccc..6ad2d8fe77 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -720,6 +720,9 @@ static void update_head(const struct ref *our, const struct ref *remote,
 	} else if (our) {
 		struct commit *c = lookup_commit_reference(the_repository,
 							   &our->old_oid);
+		/* Check if --branch specifies a non-commit. */
+		if (c == NULL)
+			die(_("unable to update HEAD (cannot find commit)"));
 		/* --branch specifies a non-branch (i.e. tags), detach HEAD */
 		update_ref(msg, "HEAD", &c->object.oid, NULL, REF_NO_DEREF,
 			   UPDATE_REFS_DIE_ON_ERR);
-- 
2.23.0