Improve handling of out-of-memory in libpq.

If an allocation fails in the main message handling loop, pqParseInput3
or pqParseInput2, it should not be treated as "not enough data available
yet". Otherwise libpq will wait indefinitely for more data to arrive from
the server, and gets stuck forever.

This isn't a complete fix - getParamDescriptions and getCopyStart still
have the same issue, but it's a step in the right direction.

Michael Paquier and me. Backpatch to all supported versions.

1 files changed, 38 insertions, 13 deletions

diff --git a/src/interfaces/libpq/fe-protocol2.c b/src/interfaces/libpq/fe-protocol2.c
index 2a6af5e41c6..365e7525d74 100644
--- a/src/interfaces/libpq/fe-protocol2.c
+++ b/src/interfaces/libpq/fe-protocol2.c
@@ -498,10 +498,17 @@ pqParseInput2(PGconn *conn)
 						conn->result = PQmakeEmptyPGresult(conn,
 														   PGRES_COMMAND_OK);
 						if (!conn->result)
-							return;
+						{
+							printfPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("out of memory"));
+							pqSaveErrorResult(conn);
+						}
+					}
+					if (conn->result)
+					{
+						strlcpy(conn->result->cmdStatus, conn->workBuffer.data,
+								CMDSTATUS_LEN);
 					}
-					strlcpy(conn->result->cmdStatus, conn->workBuffer.data,
-							CMDSTATUS_LEN);
 					checkXactStatus(conn, conn->workBuffer.data);
 					conn->asyncStatus = PGASYNC_READY;
 					break;
@@ -522,8 +529,16 @@ pqParseInput2(PGconn *conn)
 										 "unexpected character %c following empty query response (\"I\" message)",
 										 id);
 					if (conn->result == NULL)
+					{
 						conn->result = PQmakeEmptyPGresult(conn,
 														   PGRES_EMPTY_QUERY);
+						if (!conn->result)
+						{
+							printfPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext("out of memory"));
+							pqSaveErrorResult(conn);
+						}
+					}
 					conn->asyncStatus = PGASYNC_READY;
 					break;
 				case 'K':		/* secret key data from the backend */
@@ -876,14 +891,17 @@ pqGetErrorNotice2(PGconn *conn, bool isError)
 	 * Make a PGresult to hold the message.  We temporarily lie about the
 	 * result status, so that PQmakeEmptyPGresult doesn't uselessly copy
 	 * conn->errorMessage.
+	 *
+	 * NB: This allocation can fail, if you run out of memory. The rest of the
+	 * function handles that gracefully, and we still try to set the error
+	 * message as the connection's error message.
 	 */
 	res = PQmakeEmptyPGresult(conn, PGRES_EMPTY_QUERY);
-	if (!res)
-		goto failure;
-	res->resultStatus = isError ? PGRES_FATAL_ERROR : PGRES_NONFATAL_ERROR;
-	res->errMsg = pqResultStrdup(res, workBuf.data);
-	if (!res->errMsg)
-		goto failure;
+	if (res)
+	{
+		res->resultStatus = isError ? PGRES_FATAL_ERROR : PGRES_NONFATAL_ERROR;
+		res->errMsg = pqResultStrdup(res, workBuf.data);
+	}
 
 	/*
 	 * Break the message into fields.  We can't do very much here, but we can
@@ -935,15 +953,22 @@ pqGetErrorNotice2(PGconn *conn, bool isError)
 		pqClearAsyncResult(conn);
 		conn->result = res;
 		resetPQExpBuffer(&conn->errorMessage);
-		appendPQExpBufferStr(&conn->errorMessage, res->errMsg);
+		if (res && !PQExpBufferDataBroken(workBuf) && res->errMsg)
+			appendPQExpBufferStr(&conn->errorMessage, res->errMsg);
+		else
+			printfPQExpBuffer(&conn->errorMessage,
+							  libpq_gettext("out of memory"));
 		if (conn->xactStatus == PQTRANS_INTRANS)
 			conn->xactStatus = PQTRANS_INERROR;
 	}
 	else
 	{
-		if (res->noticeHooks.noticeRec != NULL)
-			(*res->noticeHooks.noticeRec) (res->noticeHooks.noticeRecArg, res);
-		PQclear(res);
+		if (res)
+		{
+			if (res->noticeHooks.noticeRec != NULL)
+				(*res->noticeHooks.noticeRec) (res->noticeHooks.noticeRecArg, res);
+			PQclear(res);
+		}
 	}
 
 	termPQExpBuffer(&workBuf);