postgres.git / summary / log / commit / refs

commit    e6fee616d47f2ce661ccba4c663f54af41548698
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Thu Jun 15 19:03:39 2017 +0000

    Fix low-probability leaks of PGresult objects in the backend.
    
    We had three occurrences of essentially the same coding pattern
    wherein we tried to retrieve a query result from a libpq connection
    without blocking.  In the case where PQconsumeInput failed (typically
    indicating a lost connection), all three loops simply gave up and
    returned, forgetting to clear any previously-collected PGresult
    object.  Since those are malloc'd not palloc'd, the oversight results
    in a process-lifespan memory leak.
    
    One instance, in libpqwalreceiver, is of little significance because
    the walreceiver process would just quit anyway if its connection fails.
    But we might as well fix it.
    
    The other two instances, in postgres_fdw, are somewhat more worrisome
    because at least in principle the scenario could be repeated, allowing
    the amount of memory leaked to build up to something worth worrying
    about.  Moreover, in these cases the loops contain CHECK_FOR_INTERRUPTS
    calls, as well as other calls that could potentially elog(ERROR),
    providing another way to exit without having cleared the PGresult.
    Here we need to add PG_TRY logic similar to what exists in quite a
    few other places in postgres_fdw.
    
    Coverity noted the libpqwalreceiver bug; I found the other two cases
    by checking all calls of PQconsumeInput.
    
    Back-patch to all supported versions as appropriate (9.2 lacks
    postgres_fdw, so this is really quite unexciting for that branch).
    
    Discussion: https://postgr.es/m/22620.1497486981@sss.pgh.pa.us


 .../replication/libpqwalreceiver/libpqwalreceiver.c        | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 5340ed064cf..cd6fdc14cad 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -286,14 +286,20 @@ libpqrcv_PQexec(const char *query)
 			 */
 			if (!libpq_select(-1))
 				continue;		/* interrupted */
+
+			/* Consume whatever data is available from the socket */
 			if (PQconsumeInput(streamConn) == 0)
-				return NULL;	/* trouble */
+			{
+				/* trouble; drop whatever we had and return NULL */
+				PQclear(lastResult);
+				return NULL;
+			}
 		}
 
 		/*
-		 * Emulate the PQexec()'s behavior of returning the last result when
-		 * there are many. Since walsender will never generate multiple
-		 * results, we skip the concatenation of error messages.
+		 * Emulate PQexec()'s behavior of returning the last result when there
+		 * are many.  Since walsender will never generate multiple results, we
+		 * skip the concatenation of error messages.
 		 */
 		result = PQgetResult(streamConn);
 		if (result == NULL)


[parent: 1fe10463d9bd]