Fix corner-case coredump in _SPI_error_callback().

I noticed that _SPI_execute_plan initially sets spierrcontext.arg = NULL,
and only fills it in some time later.  If an error were to happen in
between, _SPI_error_callback would try to dereference the null pointer.
This is unlikely --- there's not much between those points except
push-snapshot calls --- but it's clearly not impossible.  Tweak the
callback to do nothing if the pointer isn't set yet.

It's been like this for awhile, so back-patch to all supported branches.

diff --git a/src/backend/executor/spi.c b/src/backend/executor/spi.c
index 2da1cac3e215e7ff527ccbdb986a5fb6d3008332..f3da2ddd080b9524bc545ed411f1a1e7418a460a 100644 (file)
--- a/src/backend/executor/spi.c
+++ b/src/backend/executor/spi.c
@@ -2367,6 +2367,9 @@ _SPI_error_callback(void *arg)
        const char *query = (const char *) arg;
        int                     syntaxerrposition;
 
+       if (query == NULL)                      /* in case arg wasn't set yet */
+               return;
+
        /*
         * If there is a syntax error position, convert to internal syntax error;
         * otherwise treat the query as an item of context stack