[patch 2/8] allow unprivileged umount

Miklos Szeredi
2007-04-20T10:27:43Z

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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 2007-04-20 11:55:05.000000000 +0200
+++ linux/fs/namespace.c 2007-04-20 11:55:06.000000000 +0200
@@ -659,6 +659,25 @@ static int do_umount(struct vfsmount *mn
}

/*
+ * 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 (!(mnt->mnt_flags & MNT_USER))
+ return false;
+
+ if (flags & MNT_FORCE)
+ return false;
+
+ return mnt->mnt_uid == current->uid;
+}
+
+/*
* Now umount can handle mount points as well as block devices.
* This is important for filesystems which use unnamed block devices.
*
@@ -681,7 +700,7 @@ 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);

--