[src/trunk]: src/sys/fs/union Fix previous, don't copy up if the underlying n...

[hannken <hannken%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/5b2becd5ca69
branches:  trunk
changeset: 1027190:5b2becd5ca69
user:      hannken <hannken%NetBSD.org@localhost>
date:      Fri Dec 10 09:20:38 2021 +0000

description:
Fix previous, don't copy up if the underlying node is unreadable.

diffstat:

 sys/fs/union/union_vnops.c |  16 +++++++++++++---
 1 files changed, 13 insertions(+), 3 deletions(-)

diffs (40 lines):

diff -r 6c7e8d76b915 -r 5b2becd5ca69 sys/fs/union/union_vnops.c
--- a/sys/fs/union/union_vnops.c        Fri Dec 10 05:55:06 2021 +0000
+++ b/sys/fs/union/union_vnops.c        Fri Dec 10 09:20:38 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: union_vnops.c,v 1.80 2021/12/05 16:16:58 hannken Exp $ */
+/*     $NetBSD: union_vnops.c,v 1.81 2021/12/10 09:20:38 hannken Exp $ */
 
 /*
  * Copyright (c) 1992, 1993, 1994, 1995
@@ -72,7 +72,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: union_vnops.c,v 1.80 2021/12/05 16:16:58 hannken Exp $");
+__KERNEL_RCSID(0, "$NetBSD: union_vnops.c,v 1.81 2021/12/10 09:20:38 hannken Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -771,10 +771,20 @@
                }
        }
 
+       /*
+        * Copy up to prevent checking (and failing) against
+        * underlying file system mounted read only.
+        * Check for read access first to prevent implicit
+        * copy of unaccessible underlying vnode.
+        */
        if (un->un_uppervp == NULLVP &&
            (un->un_lowervp->v_type == VREG) &&
            (ap->a_accmode & VWRITE)) {
-               error = union_copyup(un, 1, ap->a_cred, curlwp);
+               vn_lock(un->un_lowervp, LK_EXCLUSIVE | LK_RETRY);
+               error = VOP_ACCESS(un->un_lowervp, VREAD, ap->a_cred);
+               VOP_UNLOCK(un->un_lowervp);
+               if (error == 0)
+                       error = union_copyup(un, 1, ap->a_cred, curlwp);
                if (error)
                        return error;
        }