2008-01-08 11:38:42

by Miklos Szeredi

Subject: [patch 2/9] unprivileged mounts: allow unprivileged umount

From: Miklos Szeredi <[email protected]>

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 <[email protected]>
---

Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c 2008-01-03 20:52:38.000000000 +0100
+++ linux/fs/namespace.c 2008-01-03 21:14:16.000000000 +0100
@@ -894,6 +894,27 @@ 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.
@@ -917,7 +938,7 @@ asmlinkage long sys_umount(char __user *
goto dput_and_out;

retval = -EPERM;
- if (!capable(CAP_SYS_ADMIN))
+ if (!permit_umount(nd.path.mnt, flags))
goto dput_and_out;

retval = do_umount(nd.path.mnt, flags);

--

2008-01-14 21:48:52

by Serge E. Hallyn

Subject: Re: [patch 2/9] unprivileged mounts: allow unprivileged umount

Quoting Miklos Szeredi ([email protected]):
> From: Miklos Szeredi <[email protected]>
>
> 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 <[email protected]>

Acked-by: Serge Hallyn <[email protected]>

> ---
>
> Index: linux/fs/namespace.c
> ===================================================================
> --- linux.orig/fs/namespace.c 2008-01-03 20:52:38.000000000 +0100
> +++ linux/fs/namespace.c 2008-01-03 21:14:16.000000000 +0100
> @@ -894,6 +894,27 @@ 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.
> @@ -917,7 +938,7 @@ asmlinkage long sys_umount(char __user *
> goto dput_and_out;
>
> retval = -EPERM;
> - if (!capable(CAP_SYS_ADMIN))
> + if (!permit_umount(nd.path.mnt, flags))
> goto dput_and_out;
>
> retval = do_umount(nd.path.mnt, flags);
>
> --