pgbench: avoid FD_ISSET on an invalid file descriptor

The original code wasn't careful to test the file descriptor returned by
PQsocket() for an invalid socket.  If an invalid socket did turn up,
that would amount to calling FD_ISSET with fd = -1, whereby undefined
behavior can be invoked.

To fix, test file descriptor for validity and stop further processing if
that fails.

Problem noticed by Coverity.

There is an existing FD_ISSET callsite that does check for invalid
sockets beforehand, but the error message reported by it was
strerror(errno); in testing the aforementioned change, that turns out to
result in "bad socket: Success" which isn't terribly helpful.  Instead
use PQerrorMessage() in both places which is more likely to contain an
useful error message.

Backpatch-through: 9.1.

diff --git a/contrib/pgbench/pgbench.c b/contrib/pgbench/pgbench.c
index 035024d6f58c269c43eebfd8e3cdd6583d638a83..9e58779cc46618ac3fb2404d3f9696268e9fb2b1 100644 (file)
--- a/contrib/pgbench/pgbench.c
+++ b/contrib/pgbench/pgbench.c
@@ -2398,7 +2398,7 @@ threadRun(void *arg)
                        sock = PQsocket(st->con);
                        if (sock < 0)
                        {
-                               fprintf(stderr, "bad socket: %s\n", strerror(errno));
+                               fprintf(stderr, "bad socket: %s", PQerrorMessage(st->con));
                                goto done;
                        }
 
@@ -2439,11 +2439,21 @@ threadRun(void *arg)
                        Command   **commands = sql_files[st->use_file];
                        int                     prev_ecnt = st->ecnt;
 
-                       if (st->con && (FD_ISSET(PQsocket(st->con), &input_mask)
-                                                       || commands[st->state]->type == META_COMMAND))
+                       if (st->con)
                        {
-                               if (!doCustom(thread, st, &result->conn_time, logfile))
-                                       remains--;      /* I've aborted */
+                               int                     sock = PQsocket(st->con);
+
+                               if (sock < 0)
+                               {
+                                       fprintf(stderr, "bad socket: %s", PQerrorMessage(st->con));
+                                       goto done;
+                               }
+                               if (FD_ISSET(sock, &input_mask) ||
+                                       commands[st->state]->type == META_COMMAND)
+                               {
+                                       if (!doCustom(thread, st, &result->conn_time, logfile))
+                                               remains--;      /* I've aborted */
+                               }
                        }
 
                        if (st->ecnt > prev_ecnt && commands[st->state]->type == META_COMMAND)