Fix array allocation bugs in SetExplainExtensionState.

If we already have an extension_state array but see a new extension_id
much larger than the highest the extension_id we've previously seen,
the old code might have failed to expand the array to a large enough
size, leading to disaster. Also, if we don't have an extension array
at all and need to create one, we should make sure that it's big enough
that we don't have to resize it instantly.

Reported-by: Tom Lane <[email protected]>
Reviewed-by: Tom Lane <[email protected]>
Discussion: http://postgr.es/m/2949591.1758570711@sss.pgh.pa.us
Backpatch-through: 18

diff --git a/src/backend/commands/explain_state.c b/src/backend/commands/explain_state.c
index 60d98d63a62e218619d05b7fb293e0eaf4dded4e..9fdeeab6436fd0e667c3b6f74ad9b34b31dc5952 100644 (file)
--- a/src/backend/commands/explain_state.c
+++ b/src/backend/commands/explain_state.c
@@ -281,7 +281,8 @@ SetExplainExtensionState(ExplainState *es, int extension_id, void *opaque)
    /* If there is no array yet, create one. */
    if (es->extension_state == NULL)
    {
-       es->extension_state_allocated = 16;
+       es->extension_state_allocated =
+           Max(16, pg_nextpower2_32(extension_id + 1));
        es->extension_state =
            palloc0(es->extension_state_allocated * sizeof(void *));
    }
@@ -291,7 +292,7 @@ SetExplainExtensionState(ExplainState *es, int extension_id, void *opaque)
    {
        int         i;
 
-       i = pg_nextpower2_32(es->extension_state_allocated + 1);
+       i = pg_nextpower2_32(extension_id + 1);
        es->extension_state = (void **)
            repalloc0(es->extension_state,
                      es->extension_state_allocated * sizeof(void *),