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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 (
"errors"
"fmt"
"io"
"io/fs"
"os"
"path/filepath"
"syscall"
"github.com/jessevdk/go-flags"
"github.com/snapcore/snapd/dirs"
"github.com/snapcore/snapd/logger"
)
var opts struct {
FromSnapConfine bool `long:"from-snap-confine"`
UserMounts bool `long:"user-mounts"`
UserID int `short:"u"`
Positionals struct {
SnapName string `positional-arg-name:"SNAP_NAME" required:"yes"`
} `positional-args:"true"`
}
// IMPORTANT: all the code in main() until bootstrap is finished may be run
// with elevated privileges when invoking snap-update-ns from snap-confine
// which grants additional capabilities.
func main() {
logger.SimpleSetup(nil)
if err := run(); err != nil {
fmt.Printf("cannot update snap namespace: %s\n", err)
os.Exit(1)
}
// END IMPORTANT
}
func parseArgs(args []string) error {
parser := flags.NewParser(&opts, flags.HelpFlag|flags.PassDoubleDash|flags.PassAfterNonOption)
_, err := parser.ParseArgs(args)
return err
}
// IMPORTANT: all the code in run() until BootStrapError() is finished may
// be run with elevated privileges when invoking snap-update-ns from
// the setuid snap-confine.
func run() error {
// There is some C code that runs before main() is started.
// That code always runs and sets an error condition if it fails.
// Here we just check for the error.
if err := BootstrapError(); err != nil {
// If there is no mount namespace to transition to let's just quit
// instantly without any errors as there is nothing to do anymore.
if err == ErrNoNamespace {
logger.Debugf("no preserved mount namespace, nothing to update")
return nil
}
return err
}
// END IMPORTANT
if err := parseArgs(os.Args[1:]); err != nil {
return err
}
setupOptInLogging(opts.Positionals.SnapName, opts.UserMounts)
logger.Debugf("snap-update-ns invoked snap:%s, fromSnapConfine:%v, userMounts:%v",
opts.Positionals.SnapName, opts.FromSnapConfine, opts.UserMounts)
// Explicitly set the umask to 0 to prevent permission bits
// being masked out when creating files and directories.
//
// While snap-confine already does this for us, we inherit
// snapd's umask when it invokes us.
syscall.Umask(0)
var upCtx MountProfileUpdateContext
if opts.UserMounts {
userUpCtx, err := NewUserProfileUpdateContext(opts.Positionals.SnapName, opts.FromSnapConfine, os.Getuid())
if err != nil {
return fmt.Errorf("cannot create user profile update context: %v", err)
}
upCtx = userUpCtx
} else {
upCtx = NewSystemProfileUpdateContext(opts.Positionals.SnapName, opts.FromSnapConfine)
}
return executeMountProfileUpdate(upCtx)
}
// setupOptInLogging configures the logger to log to an existing file.
//
// Developers or users assisting in a debug session may be asked to touch empty
// files at /run/snapd/ns/snap.$SNAP_NAME.log and
// /run/snapd/ns/snap.$SNAP_NAME.user.$UID.log.
//
// Presence of either file activates verbose debug logging of mount namespace
// operations of the specific snap, and snap-uid pair.
//
// Nothing in snapd creates or removes those files. The content may be attached
// to bug reports to be investigated by snapd developers.
func setupOptInLogging(snapName string, userMounts bool) {
var path string
if userMounts {
path = filepath.Join(dirs.SnapRunNsDir, fmt.Sprintf("snap.%s.user.%d.log", snapName, os.Getuid()))
} else {
path = filepath.Join(dirs.SnapRunNsDir, fmt.Sprintf("snap.%s.log", snapName))
}
// NOTE: This file is never closed.
f, err := os.OpenFile(path, os.O_WRONLY, 0)
if err != nil {
if !errors.Is(err, fs.ErrNotExist) {
logger.Debugf("Cannot open snap-update-ns log file: %v", err)
}
return
}
// Write logs to both os.Stderr and f. Due to how we use LoggerOptions, and
// the limited nature of the logger, os.Stderr will see all debug logs even
// if that setting is not enabled. This could be addressed with slog-based
// logger that uses a tee-like handler with distinct levels.
logger.SetLogger(logger.New(io.MultiWriter(os.Stderr, f), 0, &logger.LoggerOptions{ForceDebug: true}))
}
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