libpq: Make error checks in the new buffer draining code more robust

Check explicitly for pqsecure_read() returning an error. It shouldn't
fail, and we would've caught it in the check for a short read, but
better to be explicit so that the error message is more informative.
We also shouldn't update 'inEnd' when the read fails, although that
too is just pro forma as we will bail out and close the connection on
error.

Reported-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://www.postgresql.org/message-id/34844e8c-267c-4daf-b1e0-f26059a4a7d3@eisentraut.org
Backpatch-through: 14

diff --git a/src/interfaces/libpq/fe-misc.c b/src/interfaces/libpq/fe-misc.c
index dd7728380054a7802ee2c7ddec30f1eab5da4425..f11b58bf9c7ca960d19230583b097c569739793c 100644 (file)
--- a/src/interfaces/libpq/fe-misc.c
+++ b/src/interfaces/libpq/fe-misc.c
@@ -928,13 +928,18 @@ pqDrainPending(PGconn *conn)
 
        nread = pqsecure_read(conn, conn->inBuffer + conn->inEnd,
                                                  bytes_pending);
-       conn->inEnd += nread;
 
-       /* When there are bytes pending, the read function is not supposed to fail */
+       /*
+        * When there are bytes pending, pqsecure_read() is not supposed to fail
+        * or do a short read, but let's check anyway to be safe.
+        */
+       if (nread < 0)
+               return -1;
+       conn->inEnd += nread;
        if (nread != bytes_pending)
        {
                libpq_append_conn_error(conn,
-                                                               "drained only %zu of %zd pending bytes in transport buffer",
+                                                               "drained only %zd of %zd pending bytes in transport buffer",
                                                                nread, bytes_pending);
                return -1;
        }

diff --git a/src/interfaces/libpq/fe-secure.c b/src/interfaces/libpq/fe-secure.c
index 70faf8b2fe0eaad9ee455f705454b2e5927f5dff..1a8e2e6746e17d6399c2b8387141ae71461c8439 100644 (file)
--- a/src/interfaces/libpq/fe-secure.c
+++ b/src/interfaces/libpq/fe-secure.c
@@ -247,8 +247,9 @@ pqsecure_raw_read(PGconn *conn, void *ptr, size_t len)
  *     Return the number of bytes available in the transport buffer.
  *
  * If pqsecure_read() is called for this number of bytes, it's guaranteed to
- * return successfully without reading from the underlying socket.  See
- * pqDrainPending() for a more complete discussion of the concepts involved.
+ * return successfully with the same number of bytes, without reading from the
+ * underlying socket.  See pqDrainPending() for a more complete discussion of
+ * the concepts involved.
  */
 ssize_t
 pqsecure_bytes_pending(PGconn *conn)