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 06cc57863bddbd6012b163006f6495a241d99796..f93124b1b23ef04cc06eab56e439a1f48657e14b 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 e4d9528ac1e8316d1062c0312ba13a286c356eea..3e161506a37ff2550f1508ddb2f05e1d7d453cd4 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)