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d33346c0e6
Many tests currently implicitly rely on reading state from /proc/self/mountinfo through the system-key or other various aspects that care about what's mounted on the system. These tests currently suffer from leaking state from the host system that the unit test is being run on into the test, exposing us to a problem where we may have false positives if these tests are run on systems with the state present and the state was not properly mocked. To alleviate this, we make LoadMountInfo take no arguments and panic if it was not properly mocked during tests. The proper way to mock mountinfo now is to use MockMountInfo(), which is now exported and will do the right thing. This does mean we have to eliminate a test in osutil which was testing about the filename argument to LoadMountInfo which no longer is possible. Signed-off-by: Ian Johnson <ian.johnson@canonical.com>
94 lines
3.3 KiB
Go
94 lines
3.3 KiB
Go
// -*- Mode: Go; indent-tabs-mode: t -*-
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/*
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* Copyright (C) 2016-2018 Canonical Ltd
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 3 as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*
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*/
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package osutil
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import (
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"fmt"
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"strings"
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)
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// IsRootWritableOverlay detects if the current '/' is a writable overlay
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// (fstype is 'overlay' and 'upperdir' is specified) and returns upperdir or
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// the empty string if not used.
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//
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// Debian-based LiveCD systems use 'casper' to setup the mounts, and part of
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// this setup involves running mount commands to mount / on /cow as overlay and
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// results in AppArmor seeing '/upper' as the upperdir rather than '/cow/upper'
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// as seen in mountinfo. By the time snapd is run, we don't have enough
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// information to discover /cow through mount parent ID or st_dev (maj:min).
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// While overlay doesn't use the mount source for anything itself, casper sets
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// the mount source ('/cow' with the above) for its own purposes and we can
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// leverage this by stripping the mount source from the beginning of upperdir.
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//
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// https://www.kernel.org/doc/Documentation/filesystems/overlayfs.txt
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// man 5 proc
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//
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// Currently uses variables and Mock functions from nfs.go
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func IsRootWritableOverlay() (string, error) {
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mountinfo, err := LoadMountInfo()
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if err != nil {
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return "", fmt.Errorf("cannot parse mountinfo: %s", err)
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}
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for _, entry := range mountinfo {
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if entry.FsType == "overlay" && entry.MountDir == "/" {
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if dir, ok := entry.SuperOptions["upperdir"]; ok {
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// upperdir must be an absolute path without
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// any AppArmor regular expression (AARE)
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// characters or double quotes to be considered
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if !strings.HasPrefix(dir, "/") || strings.ContainsAny(dir, `?*[]{}^"`) {
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continue
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}
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// if mount source is path, strip it from dir
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// (for casper)
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if strings.HasPrefix(entry.MountSource, "/") {
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dir = strings.TrimPrefix(dir, strings.TrimRight(entry.MountSource, "/"))
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}
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dir = strings.TrimRight(dir, "/")
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// The resulting trimmed dir must be an
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// absolute path that is not '/'
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if len(dir) < 2 || !strings.HasPrefix(dir, "/") {
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continue
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}
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switch dir {
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case "/media/root-rw/overlay":
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// On the Ubuntu server ephemeral image, '/' is setup via
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// overlayroot (on at least 18.10), which uses a combination
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// of overlayfs and chroot. This differs from the livecd setup
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// so special case the detection logic to look for the known
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// upperdir for this configuration, and return the required
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// path. See LP: #1797218 for details.
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return "/overlay", nil
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case "/run/miso/overlay_root/upper":
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// On the Manjaro ephemeral image, '/' is setup via
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// overlayroot. This is similar to the workaround above.
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return "/upper", nil
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}
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// Make sure trailing slashes are predictably missing
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return dir, nil
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}
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}
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}
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return "", nil
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}
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