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 0ebfcca6e55317f32f9121cbdaab19051cfcf7dd..83144d9124fd7612fb1e424917300c38294830ef 100644 (file)
--- a/src/interfaces/libpq/fe-misc.c
+++ b/src/interfaces/libpq/fe-misc.c
@@ -918,13 +918,18 @@ 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)
        {
                appendPQExpBuffer(&conn->errorMessage,
-                                                 libpq_gettext("drained only %zu of %zd pending bytes in transport buffer\n"),
+                                                 libpq_gettext("drained only %zd of %zd pending bytes in transport buffer\n"),
                                                  nread, bytes_pending);
                return -1;
        }

diff --git a/src/interfaces/libpq/fe-secure.c b/src/interfaces/libpq/fe-secure.c
index acf01433ffcacacc0c9625e2f5ea33c1f42cea6a..f7e1c9beeacf1b07d0410f14c33639e15f71f4dd 100644 (file)
--- a/src/interfaces/libpq/fe-secure.c
+++ b/src/interfaces/libpq/fe-secure.c
@@ -288,8 +288,9 @@ 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)