From c1cbf1992b278c9019b6a87337b59f95b252362c Mon Sep 17 00:00:00 2001
From: kre <kre@NetBSD.org>
Date: Sat, 22 Apr 2017 16:02:39 +0000
Subject: [PATCH] Keep track of the biggest fd used by, or available to, the
 user/script and use that to control which fd's are examined by a (bare)
 fdflags (with no fd args).

Usually this will mean that fdflags will no longer show the shell's
internal use fds, only user fds.

This is only a partial fix however, a user can easily discover the
shell's fd usage (eg: using fstat) and can then still use fdflags to
manipulate those fds (or even send output to them).

The shell needs to monitor its own fd usage better, and keep out of
the way of user fds - coming sometime later...
---
 bin/sh/main.c  | 10 ++++++++--
 bin/sh/redir.c | 15 ++++++---------
 bin/sh/redir.h |  4 +++-
 3 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/bin/sh/main.c b/bin/sh/main.c
index 9df247783db5..09a8b9a89ffd 100644
--- a/bin/sh/main.c
+++ b/bin/sh/main.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: main.c,v 1.67 2016/05/09 21:03:10 kre Exp $	*/
+/*	$NetBSD: main.c,v 1.68 2017/04/22 16:02:39 kre Exp $	*/
 
 /*-
  * Copyright (c) 1991, 1993
@@ -42,7 +42,7 @@ __COPYRIGHT("@(#) Copyright (c) 1991, 1993\
 #if 0
 static char sccsid[] = "@(#)main.c	8.7 (Berkeley) 7/19/95";
 #else
-__RCSID("$NetBSD: main.c,v 1.67 2016/05/09 21:03:10 kre Exp $");
+__RCSID("$NetBSD: main.c,v 1.68 2017/04/22 16:02:39 kre Exp $");
 #endif
 #endif /* not lint */
 
@@ -77,11 +77,13 @@ __RCSID("$NetBSD: main.c,v 1.67 2016/05/09 21:03:10 kre Exp $");
 #include "mystring.h"
 #include "exec.h"
 #include "cd.h"
+#include "redir.h"
 
 #define PROFILE 0
 
 int rootpid;
 int rootshell;
+int max_user_fd;
 #if PROFILE
 short profile_buf[16384];
 extern int etext();
@@ -111,6 +113,10 @@ main(int argc, char **argv)
 	uid = getuid();
 	gid = getgid();
 
+	max_user_fd = fcntl(0, F_MAXFD);
+	if (max_user_fd < 2)
+		max_user_fd = 2;
+
 	setlocale(LC_ALL, "");
 
 	posix = getenv("POSIXLY_CORRECT") != NULL;
diff --git a/bin/sh/redir.c b/bin/sh/redir.c
index 36c936857666..33b2de0766dd 100644
--- a/bin/sh/redir.c
+++ b/bin/sh/redir.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: redir.c,v 1.52 2017/04/22 15:54:53 kre Exp $	*/
+/*	$NetBSD: redir.c,v 1.53 2017/04/22 16:02:39 kre Exp $	*/
 
 /*-
  * Copyright (c) 1991, 1993
@@ -37,7 +37,7 @@
 #if 0
 static char sccsid[] = "@(#)redir.c	8.2 (Berkeley) 5/4/95";
 #else
-__RCSID("$NetBSD: redir.c,v 1.52 2017/04/22 15:54:53 kre Exp $");
+__RCSID("$NetBSD: redir.c,v 1.53 2017/04/22 16:02:39 kre Exp $");
 #endif
 #endif /* not lint */
 
@@ -189,6 +189,8 @@ redirect(union node *redir, int flags)
 	}
 	for (n = redir ; n ; n = n->nfile.next) {
 		fd = n->nfile.fd;
+		if (fd > max_user_fd)
+			max_user_fd = fd;
 		if ((n->nfile.type == NTOFD || n->nfile.type == NFROMFD) &&
 		    n->ndup.dupfd == fd) {
 			/* redirect from/to same file descriptor */
@@ -738,22 +740,17 @@ fdflagscmd(int argc, char *argv[])
 		parseflags(setflags, &pos, &neg);
 
 	if (argc == 0) {
-		int maxfd;
+		int i;
 
 		if (setflags)
 			goto msg;
 
 		/*
-		 * XXX  this has to go, maxfd might be 700 (or something)
-		 *
 		 * XXX  we should only ever operate on user defined fds
 		 * XXX  not on sh internal fds that might be open.
 		 * XXX  but for that we need to know their range (later)
 		 */
-		maxfd = fcntl(0, F_MAXFD);
-		if (maxfd == -1)
-			error("Can't get max fd (%s)", strerror(errno));
-		for (int i = 0; i <= maxfd; i++)
+		for (i = 0; i <= max_user_fd; i++)
 			printone(i, 0, verbose, 1);
 		return 0;
 	}
diff --git a/bin/sh/redir.h b/bin/sh/redir.h
index dd53ae355560..2c42adfa0729 100644
--- a/bin/sh/redir.h
+++ b/bin/sh/redir.h
@@ -1,4 +1,4 @@
-/*	$NetBSD: redir.h,v 1.21 2016/05/12 13:31:37 kre Exp $	*/
+/*	$NetBSD: redir.h,v 1.22 2017/04/22 16:02:39 kre Exp $	*/
 
 /*-
  * Copyright (c) 1991, 1993
@@ -47,3 +47,5 @@ int fd0_redirected_p(void);
 void clearredir(int);
 int movefd(int, int);
 int to_upper_fd(int);
+
+int max_user_fd;		/* highest fd used by user */