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 8b11cef1c036a5076afe0c4daa4df27426996023..87cbe5a11f18325937d0fc4d5ec3dddc42742ffe 100644 (file)
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1133,7 +1133,7 @@ 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];