Fix off-by-one loop termination condition in pg_stat_get_subscription().

pg_stat_get_subscription scanned one more LogicalRepWorker array entry
than is really allocated.  In the worst case this could lead to SIGSEGV,
if the LogicalRepCtx data structure is near the end of shared memory.
That seems quite unlikely though (thanks to the ordering of calls in
CreateSharedMemoryAndSemaphores) and we've heard no field reports of it.
A more likely misbehavior is one row of garbage data in the function's
result, but even that is not real likely because of the check that the
pid field matches some live backend.

Report and fix by Kuntal Ghosh.  This bug is old, so back-patch
to all supported branches.

Discussion: https://postgr.es/m/CAGz5QCJykEDzW6jQK6Yz7Qh_PMtD=95de_7QoocbVR2Qy8hWZA@mail.gmail.com

diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 6d97b743103c3061900e67ade815a92db533448e..19e5296106ddb4d975d831e10117f6fbca748e20 100644 (file)
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1148,7 +1148,7 @@ pg_stat_get_subscription(PG_FUNCTION_ARGS)
        /* Make sure we get consistent view of the workers. */
        LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
 
-       for (i = 0; i <= max_logical_replication_workers; i++)
+       for (i = 0; i < max_logical_replication_workers; i++)
        {
                /* for each row */
                Datum           values[PG_STAT_GET_SUBSCRIPTION_COLS];