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// -*- Mode: Go; indent-tabs-mode: t -*-
/*
* Copyright (C) 2017 Canonical Ltd
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 3 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
package main
import (
"fmt"
"github.com/snapcore/snapd/dirs"
"github.com/snapcore/snapd/snap"
)
// SystemProfileUpdateContext contains information about update to system-wide mount namespace.
type SystemProfileUpdateContext struct {
CommonProfileUpdateContext
}
// NewSystemProfileUpdateContext returns encapsulated information for performing a per-user mount namespace update.
func NewSystemProfileUpdateContext(instanceName string, fromSnapConfine bool) *SystemProfileUpdateContext {
return &SystemProfileUpdateContext{CommonProfileUpdateContext: CommonProfileUpdateContext{
instanceName: instanceName,
fromSnapConfine: fromSnapConfine,
currentProfilePath: currentSystemProfilePath(instanceName),
desiredProfilePath: desiredSystemProfilePath(instanceName),
}}
}
// Assumptions returns information about file system mutability rules.
//
// System mount profiles can write to /tmp (this is required for constructing
// writable mimics) to /var/snap (where $SNAP_DATA is for services), /snap/$SNAP_NAME,
// and, in case of instances, /snap/$SNAP_INSTANCE_NAME.
func (upCtx *SystemProfileUpdateContext) Assumptions() *Assumptions {
// Allow creating directories related to this snap name.
//
// Note that we allow /var/snap instead of /var/snap/$SNAP_NAME because
// content interface connections can readily create missing mount points on
// both sides of the interface connection.
//
// We scope /snap/$SNAP_NAME because only one side of the connection can be
// created, as snaps are read-only, the mimic construction will kick-in and
// create the missing directory but this directory is only visible from the
// snap that we are operating on (either plug or slot side, the point is,
// the mount point is not universally visible).
//
// /snap/$SNAP_NAME needs to be there as the code that creates such mount
// points must traverse writable host filesystem that contains /snap/*/ and
// normally such access is off-limits. This approach allows /snap/foo
// without allowing /snap/bin, for example.
//
// /snap/$SNAP_INSTANCE_NAME and /snap/$SNAP_NAME are added to allow
// remapping for parallel installs only when the snap has an instance key
as := &Assumptions{}
instanceName := upCtx.InstanceName()
as.AddUnrestrictedPaths("/tmp", "/var/snap", "/snap/"+instanceName)
if snapName := snap.InstanceSnap(instanceName); snapName != instanceName {
as.AddUnrestrictedPaths("/snap/" + snapName)
}
// Allow snap-update-ns to write to host's /tmp directory. This is
// specifically here to allow two snaps to share X11 sockets that are placed
// in the /tmp/.X11-unix/ directory in the private /tmp directories provided
// by snap-confine. The X11 interface cannot offer a precise permission for
// the slot-side snap, as there is no mechanism to convey this information.
// As such, provide write access to all of /tmp.
as.AddUnrestrictedPaths("/var/lib/snapd/hostfs/tmp")
as.AddModeHint("/var/lib/snapd/hostfs/tmp/snap-private-tmp/snap.*", 0700)
as.AddModeHint("/var/lib/snapd/hostfs/tmp/snap-private-tmp/snap.*/tmp", 1777)
// This is to ensure that unprivileged users can create the socket. This
// permission only matters if the plug-side app constructs its mount
// namespace before the slot-side app is launched.
as.AddModeHint("/var/lib/snapd/hostfs/tmp/snap-private-tmp/snap.*/tmp/.X11-unix", 1777)
return as
}
// desiredSystemProfilePath returns the path of the fstab-like file with the desired, system-wide mount profile for a snap.
func desiredSystemProfilePath(snapName string) string {
return fmt.Sprintf("%s/snap.%s.fstab", dirs.SnapMountPolicyDir, snapName)
}
// currentSystemProfilePath returns the path of the fstab-like file with the applied, system-wide mount profile for a snap.
func currentSystemProfilePath(snapName string) string {
return fmt.Sprintf("%s/snap.%s.fstab", dirs.SnapRunNsDir, snapName)
}
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