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


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