On Mon, Mar 28, 2011 at 04:23:20PM +0200, Miklos Szeredi wrote:
> On Mon, 2011-03-28 at 16:04 +0200, Petr Uzel wrote:
> > Hi all,
> >
> > I hacked the following patch with which it is possible to use
> > "umount $dir" instead of "fusermount -u $dir", which IMHO is an
> > improvement in usability. It seems to work (at least for me), however,
> > I have to admit that I don't like it very much, because:
> > - it complicates umount
> > - duplicates code from fusermount
>
> And this is not the only one that would have to be duplicated. The
> mount and umount races that were fixed in fusermount in recently and not
> so recently would also have to be added to util-linux, which would
> actually be a good thing, since in theory they could affect fstab based
> user mounts as well (though that is much more unlikely than with fuse,
> where the user chooses the mountpoint).
Maybe we need to call umount2() with UMOUNT_NOFOLLOW flag for
non-root users in umount(8). I think it should be enough for
umount(8) (where almost all is controlled by system admin in fstab).
See below. Comments?
Karel
>From 5cf67485d23dc4547eb5e54cbe96cc60837e36af Mon Sep 17 00:00:00 2001
From: Karel Zak <kzak@xxxxxxxxxx>
Date: Tue, 29 Mar 2011 10:19:56 +0200
Subject: [PATCH] umount: use UMOUNT_NOFOLLOW for non-root users
Signed-off-by: Karel Zak <kzak@xxxxxxxxxx>
---
mount/umount.c | 44 ++++++++++++++++++++++++++++++++++++--------
1 files changed, 36 insertions(+), 8 deletions(-)
diff --git a/mount/umount.c b/mount/umount.c
index 42671f4..0660b20 100644
--- a/mount/umount.c
+++ b/mount/umount.c
@@ -45,15 +45,22 @@ umount2(const char *path, int flags) {
}
#endif /* __NR_umount2 */
-#if !defined(MNT_FORCE)
-/* dare not try to include <linux/mount.h> -- lots of errors */
-#define MNT_FORCE 1
+#ifndef MNT_FORCE
+# define MNT_FORCE 0x00000001 /* Attempt to forcibily umount */
#endif
#endif /* MNT_FORCE */
-#if !defined(MNT_DETACH)
-#define MNT_DETACH 2
+#ifndef MNT_DETACH
+# define MNT_DETACH 0x00000002 /* Just detach from the tree */
+#endif
+
+#ifndef UMOUNT_NOFOLLOW
+# define UMOUNT_NOFOLLOW 0x00000008 /* Don't follow symlink on umount */
+#endif
+
+#ifndef UMOUNT_UNUSED
+#define UMOUNT_UNUSED 0x80000000 /* Flag guaranteed to be unused */
#endif
@@ -197,6 +204,21 @@ static void complain(int err, const char *dev) {
}
}
+/* Check whether the kernel supports UMOUNT_NOFOLLOW flag */
+static int umount_nofollow_support(void)
+{
+ int res = umount2("", UMOUNT_UNUSED);
+ if (res != -1 || errno != EINVAL)
+ return 0;
+
+ res = umount2("", UMOUNT_NOFOLLOW);
+ if (res != -1 || errno != ENOENT)
+ return 0;
+
+ return 1;
+}
+
+
/* Umount a single device. Return a status code, so don't exit
on a non-fatal error. We lock/unlock around each umount. */
static int
@@ -206,6 +228,7 @@ umount_one (const char *spec, const char *node, const char *type,
int isroot;
int res = 0;
int status;
+ int extra_flags = 0;
const char *loopdev;
int myloop = 0;
@@ -237,15 +260,18 @@ umount_one (const char *spec, const char *node, const char *type,
if (delloop && is_loop_device(spec))
myloop = 1;
+ if (restricted && umount_nofollow_support())
+ extra_flags |= UMOUNT_NOFOLLOW;
+
if (lazy) {
- res = umount2 (node, MNT_DETACH);
+ res = umount2 (node, MNT_DETACH | extra_flags);
if (res < 0)
umnt_err = errno;
goto writemtab;
}
if (force) { /* only supported for NFS */
- res = umount2 (node, MNT_FORCE);
+ res = umount2 (node, MNT_FORCE | extra_flags);
if (res == -1) {
int errsv = errno;
perror("umount2");
@@ -256,7 +282,9 @@ umount_one (const char *spec, const char *node, const char *type,
res = umount (node);
}
}
- } else
+ } else if (extra_flags)
+ res = umount2 (node, extra_flags);
+ else
res = umount (node);
if (res < 0)
--
1.7.3.4
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