interfaces: add cifs-mount interface (#5340)

Details at https://forum.snapcraft.io/t/interface-mount-umount-cifs-share-permission/5689

interfaces/builtin/cifs_mount.go

@@ -0,0 +1,74 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2018 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 builtin
+
+const cifsMountSummary = `allows mounting and unmounting CIFS filesystems`
+
+const cifsMountBaseDeclarationSlots = `
+  cifs-mount:
+    allow-installation:
+      slot-snap-type:
+        - core
+    deny-auto-connection: true
+`
+
+const cifsMountConnectedPlugSecComp = `
+# Description: Allow mount and umount syscall access.
+mount
+umount
+umount2
+`
+
+const cifsMountConnectedPlugAppArmor = `
+# Description: Allow mounting and unmounting CIFS filesystems.
+
+# Required for mounts and unmounts
+capability sys_admin,
+
+# Allow mounts to our snap-specific writable directories
+mount fstype=cifs //** -> /var/snap/@{SNAP_NAME}/@{SNAP_REVISION}/{,**},
+mount fstype=cifs //** -> /var/snap/@{SNAP_NAME}/common/{,**},
+
+# NOTE: due to LP: #1613403, fstype is not mediated and as such, these rules
+# allow, for example, unmounting bind mounts from the content interface
+umount /var/snap/@{SNAP_NAME}/@{SNAP_REVISION}/{,**},
+umount /var/snap/@{SNAP_NAME}/common/{,**},
+
+# Due to an unsolved issue with namespace awareness of libmount the unmount tries to access
+# /run/mount/utab but fails. The resulting apparmor warning can be ignored. The log warning
+# was not removed via an explicit deny to not interfere with other interfaces which might
+# decide to allow access (deny rules have precedence).
+#  - https://github.com/snapcore/snapd/pull/5340#issuecomment-398071797
+#  - https://forum.snapcraft.io/t/namespace-awareness-of-run-mount-utab-and-libmount/5987
+#deny /run/mount/utab w,
+`
+
+func init() {
+	registerIface(&commonInterface{
+		name:                  "cifs-mount",
+		summary:               cifsMountSummary,
+		implicitOnCore:        true,
+		implicitOnClassic:     true,
+		baseDeclarationSlots:  cifsMountBaseDeclarationSlots,
+		connectedPlugAppArmor: cifsMountConnectedPlugAppArmor,
+		connectedPlugSecComp:  cifsMountConnectedPlugSecComp,
+		reservedForOS:         true,
+	})
+}

interfaces/builtin/cifs_mount_test.go

@@ -0,0 +1,107 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2016-2017 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 builtin_test
+
+import (
+	. "gopkg.in/check.v1"
+
+	"github.com/snapcore/snapd/interfaces"
+	"github.com/snapcore/snapd/interfaces/apparmor"
+	"github.com/snapcore/snapd/interfaces/builtin"
+	"github.com/snapcore/snapd/interfaces/seccomp"
+	"github.com/snapcore/snapd/snap"
+	"github.com/snapcore/snapd/testutil"
+)
+
+type CifsMountInterfaceSuite struct {
+	iface    interfaces.Interface
+	slotInfo *snap.SlotInfo
+	slot     *interfaces.ConnectedSlot
+	plugInfo *snap.PlugInfo
+	plug     *interfaces.ConnectedPlug
+}
+
+const cifsMountConsumerYaml = `name: consumer
+version: 0
+apps:
+ app:
+  plugs: [cifs-mount]
+`
+
+const cifsMountCoreYaml = `name: core
+version: 0
+type: os
+slots:
+  cifs-mount:
+`
+
+var _ = Suite(&CifsMountInterfaceSuite{
+	iface: builtin.MustInterface("cifs-mount"),
+})
+
+func (s *CifsMountInterfaceSuite) SetUpTest(c *C) {
+	s.plug, s.plugInfo = MockConnectedPlug(c, cifsMountConsumerYaml, nil, "cifs-mount")
+	s.slot, s.slotInfo = MockConnectedSlot(c, cifsMountCoreYaml, nil, "cifs-mount")
+}
+
+func (s *CifsMountInterfaceSuite) TestName(c *C) {
+	c.Assert(s.iface.Name(), Equals, "cifs-mount")
+}
+
+func (s *CifsMountInterfaceSuite) TestSanitizeSlot(c *C) {
+	c.Assert(interfaces.BeforePrepareSlot(s.iface, s.slotInfo), IsNil)
+	slot := &snap.SlotInfo{
+		Snap:      &snap.Info{SuggestedName: "some-snap"},
+		Name:      "cifs-mount",
+		Interface: "cifs-mount",
+	}
+	c.Assert(interfaces.BeforePrepareSlot(s.iface, slot), ErrorMatches,
+		"cifs-mount slots are reserved for the core snap")
+}
+
+func (s *CifsMountInterfaceSuite) TestSanitizePlug(c *C) {
+	c.Assert(interfaces.BeforePreparePlug(s.iface, s.plugInfo), IsNil)
+}
+
+func (s *CifsMountInterfaceSuite) TestAppArmorSpec(c *C) {
+	spec := &apparmor.Specification{}
+	c.Assert(spec.AddConnectedPlug(s.iface, s.plug, s.slot), IsNil)
+	c.Assert(spec.SecurityTags(), DeepEquals, []string{"snap.consumer.app"})
+	c.Assert(spec.SnippetForTag("snap.consumer.app"), testutil.Contains, `#deny /run/mount/utab w,`)
+}
+
+func (s *CifsMountInterfaceSuite) TestSecCompSpec(c *C) {
+	spec := &seccomp.Specification{}
+	c.Assert(spec.AddConnectedPlug(s.iface, s.plug, s.slot), IsNil)
+	c.Assert(spec.SecurityTags(), DeepEquals, []string{"snap.consumer.app"})
+	c.Assert(spec.SnippetForTag("snap.consumer.app"), testutil.Contains, "umount2\n")
+}
+
+func (s *CifsMountInterfaceSuite) TestStaticInfo(c *C) {
+	si := interfaces.StaticInfoOf(s.iface)
+	c.Assert(si.ImplicitOnCore, Equals, true)
+	c.Assert(si.ImplicitOnClassic, Equals, true)
+	c.Assert(si.Summary, Equals, `allows mounting and unmounting CIFS filesystems`)
+	c.Assert(si.BaseDeclarationSlots, testutil.Contains, "cifs-mount")
+}
+
+func (s *CifsMountInterfaceSuite) TestInterfaces(c *C) {
+	c.Check(builtin.Interfaces(), testutil.DeepContains, s.iface)
+}

tests/lib/snaps/test-snapd-policy-app-consumer/meta/snap.yaml

@@ -41,6 +41,9 @@ apps:
   camera:
     command: bin/run
     plugs: [ camera ]
+  cifs-mount:
+    command: bin/run
+    plugs: [ cifs-mount ]
   classic-support:
     command: bin/run
     plugs: [ classic-support ]