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c3e214005e
This is where they actually belong, since having the mocking at the osutil level guarantees that the mocking is effective for all packages calling into osutil.
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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var isRootWritableOverlay = func() (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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