Make contrib/xml2 use core xml.c's error handler, when available (that is,

in versions >= 8.3).  The core code is more robust and efficient than what
was there before, and this also reduces risks involved in swapping different
libxml error handler settings.

Before 8.3, there is still some risk of problems if add-on modules such as
Perl invoke libxml without setting their own error handler.  Given the lack
of reports I'm not sure there's a risk in practice, so I didn't take the
step of actually duplicating the core code into older contrib/xml2 branches.
Instead I just tweaked the existing code to ensure it didn't leave a dangling
pointer to short-lived memory when throwing an error.

1 files changed, 12 insertions, 1 deletions

diff --git a/contrib/xml2/xpath.c b/contrib/xml2/xpath.c
index 25cc7f9377b..51069adfc52 100644
--- a/contrib/xml2/xpath.c
+++ b/contrib/xml2/xpath.c
@@ -100,9 +100,20 @@ elog_error(const char *explain, bool force)
 					(errcode(ERRCODE_EXTERNAL_ROUTINE_EXCEPTION),
 					 errmsg("%s", explain)));
 		else
+		{
+			/*
+			 * Ensure pgxml_errorMsg is reset to null before we give up
+			 * control.  This provides some protection against crashes if
+			 * pgxml_errorHandler is invoked again later, perhaps as a
+			 * result of other modules' use of libxml.
+			 */
+			char   *msg = pgxml_errorMsg;
+
+			pgxml_errorMsg = NULL;
 			ereport(ERROR,
 					(errcode(ERRCODE_EXTERNAL_ROUTINE_EXCEPTION),
-					 errmsg("%s: %s", explain, pgxml_errorMsg)));
+					 errmsg("%s: %s", explain, msg)));
+		}
 	}
 }