refs: reject ref updates while GIT_QUARANTINE_PATH is set

As documented in git-receive-pack(1), updating a ref from
within the pre-receive hook is dangerous and can corrupt
your repo. This patch forbids ref updates entirely during
the hook to make it harder for adventurous hook writers to
shoot themselves in the foot.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/refs.c b/refs.c
index 5ffdd778d97..916b0d5fa53 100644
--- a/refs.c
+++ b/refs.c
@@ -1465,6 +1465,12 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 {
 	struct ref_store *refs = get_ref_store(NULL);
 
+	if (getenv(GIT_QUARANTINE_ENVIRONMENT)) {
+		strbuf_addstr(err,
+			      _("ref updates forbidden inside quarantine environment"));
+		return -1;
+	}
+
 	return refs->be->transaction_commit(refs, transaction, err);
 }