[v3,1/9] refs: fix segfault when aborting empty transaction

Commit Message

Patrick Steinhardt April 2, 2020, 7:09 a.m. UTC

When cleaning up a transaction that has no updates queued, then the
transaction's backend data will not have been allocated. We correctly
handle this for the packed backend, where the cleanup function checks
whether the backend data has been allocated at all -- if not, then there
is nothing to clean up. For the files backend we do not check this and
as a result will hit a segfault due to dereferencing a `NULL` pointer
when cleaning up such a transaction.

Fix the issue by checking whether `backend_data` is set in the files
backend, too.

Signed-off-by: Patrick Steinhardt <[e-mail]>
---
 refs/files-backend.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

Patch

diff --git a/refs/files-backend.c b/refs/files-backend.c
index 561c33ac8a..6516c7bc8c 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -2565,17 +2565,19 @@  static void files_transaction_cleanup(struct files_ref_store *refs,
 		}
 	}
 
-	if (backend_data->packed_transaction &&
-	    ref_transaction_abort(backend_data->packed_transaction, &err)) {
-		error("error aborting transaction: %s", err.buf);
-		strbuf_release(&err);
+	if (backend_data) {
+		if (backend_data->packed_transaction &&
+		    ref_transaction_abort(backend_data->packed_transaction, &err)) {
+			error("error aborting transaction: %s", err.buf);
+			strbuf_release(&err);
+		}
+
+		if (backend_data->packed_refs_locked)
+			packed_refs_unlock(refs->packed_ref_store);
+
+		free(backend_data);
 	}
 
-	if (backend_data->packed_refs_locked)
-		packed_refs_unlock(refs->packed_ref_store);
-
-	free(backend_data);
-
 	transaction->state = REF_TRANSACTION_CLOSED;
 }