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authorTom Lane <tgl@sss.pgh.pa.us>2017-06-15 15:03:39 -0400
committerTom Lane <tgl@sss.pgh.pa.us>2017-06-15 15:03:52 -0400
commita3bed62d44f83283414a82717bc8e96e9f398dcc (patch)
tree6d6c080ab0dcf3ae350feebfc9eccb11ce4b7580 /src
parent07fb943335f3cdd11a9146ae6fdee237cc83c5f6 (diff)
downloadpostgresql-a3bed62d44f83283414a82717bc8e96e9f398dcc.tar.gz
postgresql-a3bed62d44f83283414a82717bc8e96e9f398dcc.zip
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
Diffstat (limited to 'src')
-rw-r--r--src/backend/replication/libpqwalreceiver/libpqwalreceiver.c12
1 files changed, 9 insertions, 3 deletions
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 7509b4fe60a..f6fa0e4c16a 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -591,13 +591,19 @@ libpqrcv_PQexec(PGconn *streamConn, const char *query)
ResetLatch(MyLatch);
CHECK_FOR_INTERRUPTS();
}
+
+ /* 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. We are fine with returning just last error message.
+ * Emulate PQexec()'s behavior of returning the last result when there
+ * are many. We are fine with returning just last error message.
*/
result = PQgetResult(streamConn);
if (result == NULL)