Date: Wed, 11 Apr 2001 19:15:28 +0200 (CEST) From: olli@fromme.com To: FreeBSD-gnats-submit@freebsd.org Subject: bin/26498: Fix for bug in union mounts (mout -o union) Message-ID: <200104111715.f3BHFST88472@monos.secnetix.net>
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>Number: 26498
>Category: bin
>Synopsis: Fix for bug in union mounts (mout -o union)
>Confidential: no
>Severity: non-critical
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: change-request
>Submitter-Id: current-users
>Arrival-Date: Wed Apr 11 10:20:01 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator: Oliver Fromme
>Release: FreeBSD 4.3-RC2-LEHMANNS
>Organization:
My head is still at the top, and the feets are at the bottom.
>Environment:
The fix presented in this PR applies to 4-stable
as well as 5-current.
>Description:
When you mount a directory on top of another, using the
"union" option to the mount command (I'm NOT talking
about UNIONFS!), then all entries which are present in
both directories appear twice, like this:
$ ls -a
. .. bar bar1 baz baz1 foo foo1
. .. bar bar2 baz baz2 foo foo2
It is particularly disturbing that "." and ".." appear
twice, even if the directories are otherwise disjunct.
Same problem with /usr/bin/find, /bin/sh (``echo *'')
and all other tools that read and traverse directories.
The culprit is in src/lib/libc/gen/opendir.c in the
function __opendir2(). Look at the variable "unionstack"
(near line 110). It is correctly set to 1 in the case of
a UNIONFS -- in this case the code removes duplicates.
However, it doesn't handle the case of a union mount.
>How-To-Repeat:
/* Create two small vnode filesystems, /bin/sh syntax: */
for i in 0 1; do
dd if=/dev/zero of=fs$i.vn bs=1m count=1
vnconfig -s labels -c vn$i fs$i.vn
disklabel -r -w vn$i auto
newfs /dev/vn${i}c
done
/* Mount them over each other: */
mkdir fs
mount /dev/vn0c fs
mount -o union /dev/vn1c fs
ls -a
. . .. ..
/* Note that "." and ".." appear twice. */
>Fix:
The following patch fixes the problem by simply checking
if the MNT_UNION flag is set in the statfs struct.
The patch is against rev. 1.10 (4-stable as of 2000-04-10).
I have had a look at the code in current, and the fix
should be applicable there, too. I haven't actually
tested it, due to lack of a -current machine, but the
fix is trivial enough for me to be sure that it should
work. :-)
I have this code in production on a box with several
jails, all of them containing union-mounted filesystems,
and everything works fine.
*phew* Such a long PR for a one-line fix ...
--- src/lib/libc/gen/opendir.c.orig Fri Jan 28 00:06:18 2000
+++ src/lib/libc/gen/opendir.c Wed Apr 11 18:44:26 2001
@@ -110,7 +110,8 @@
if (fstatfs(fd, &sfb) < 0)
goto fail;
- unionstack = !strcmp(sfb.f_fstypename, "union");
+ unionstack = !strcmp(sfb.f_fstypename, "union")
+ || (sfb.f_flags & MNT_UNION);
} else {
unionstack = 0;
}
>Release-Note:
>Audit-Trail:
>Unformatted:
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