From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Thu, 9 Jul 2026 15:34:27 +0000 (+0300)
Subject: libpq: Make error checks in the new buffer draining code more robust
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=bab0a2db733502da5663c5aef38976cbf8711707;p=thirdparty%2Fpostgresql.git

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 ea4f9525501..e7231d834f1 100644
--- a/src/interfaces/libpq/fe-misc.c
+++ b/src/interfaces/libpq/fe-misc.c
@@ -913,13 +913,18 @@ 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 f68c2d4d12c..c86341a4bf5 100644
--- a/src/interfaces/libpq/fe-secure.c
+++ b/src/interfaces/libpq/fe-secure.c
@@ -262,8 +262,9 @@ 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)