From: Miklos Szeredi <mszeredi@suse.cz>
The owner doesn't need sysadmin capabilities to call umount().
Similar behavior as umount(8) on mounts having "user=UID" option in /etc/mtab.

The difference is that umount also checks /etc/fstab, presumably to exclude

another mount on the same mountpoint.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

---
Index: linux/fs/namespace.c

===================================================================

--- linux.orig/fs/namespace.c	2007-04-26 13:10:48.000000000 +0200

+++ linux/fs/namespace.c	2007-04-26 13:16:21.000000000 +0200

@@ -658,6 +658,27 @@ static int do_umount(struct vfsmount *mn

 	return retval;

 }
+static bool is_mount_owner(struct vfsmount *mnt, uid_t uid)

+{

+	return (mnt->mnt_flags & MNT_USER) && mnt->mnt_uid == uid;

+}

+

+/*

+ * umount is permitted for

+ *  - sysadmin

+ *  - mount owner, if not forced umount

+ */

+static bool permit_umount(struct vfsmount *mnt, int flags)

+{

+	if (capable(CAP_SYS_ADMIN))

+		return true;

+

+	if (flags & MNT_FORCE)

+		return false;

+

+	return is_mount_owner(mnt, current->fsuid);

+}

+

 /*

  * Now umount can handle mount points as well as block devices.

  * This is important for filesystems which use unnamed block devices.

@@ -681,7 +702,7 @@ asmlinkage long sys_umount(char __user *

 		goto dput_and_out;
 	retval = -EPERM;

-	if (!capable(CAP_SYS_ADMIN))

+	if (!permit_umount(nd.mnt, flags))

 		goto dput_and_out;
 	retval = do_umount(nd.mnt, flags);
--

-