github.com/rigado/snapd@v2.42.5-go-mod+incompatible/usersession/userd/helpers.go (about)

     1  // -*- Mode: Go; indent-tabs-mode: t -*-
     2  
     3  /*
     4   * Copyright (C) 2017 Canonical Ltd
     5   *
     6   * This program is free software: you can redistribute it and/or modify
     7   * it under the terms of the GNU General Public License version 3 as
     8   * published by the Free Software Foundation.
     9   *
    10   * This program is distributed in the hope that it will be useful,
    11   * but WITHOUT ANY WARRANTY; without even the implied warranty of
    12   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    13   * GNU General Public License for more details.
    14   *
    15   * You should have received a copy of the GNU General Public License
    16   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
    17   *
    18   */
    19  
    20  package userd
    21  
    22  import (
    23  	"bufio"
    24  	"fmt"
    25  	"os"
    26  	"path/filepath"
    27  	"strings"
    28  
    29  	"github.com/godbus/dbus"
    30  
    31  	"github.com/snapcore/snapd/dirs"
    32  )
    33  
    34  var snapFromSender = snapFromSenderImpl
    35  
    36  func snapFromSenderImpl(conn *dbus.Conn, sender dbus.Sender) (string, error) {
    37  	pid, err := connectionPid(conn, sender)
    38  	if err != nil {
    39  		return "", fmt.Errorf("cannot get connection pid: %v", err)
    40  	}
    41  	snap, err := snapFromPid(pid)
    42  	if err != nil {
    43  		return "", fmt.Errorf("cannot find snap for connection: %v", err)
    44  	}
    45  	// Check that the sender is still connected to the bus: if it
    46  	// has disconnected between the GetConnectionUnixProcessID
    47  	// call and when we poked around in /proc, then it is possible
    48  	// that the process ID was reused.
    49  	if !nameHasOwner(conn, sender) {
    50  		return "", fmt.Errorf("sender is no longer connected to the bus")
    51  	}
    52  	return snap, nil
    53  }
    54  
    55  func connectionPid(conn *dbus.Conn, sender dbus.Sender) (pid int, err error) {
    56  	call := conn.BusObject().Call("org.freedesktop.DBus.GetConnectionUnixProcessID", 0, sender)
    57  	if call.Err != nil {
    58  		return 0, call.Err
    59  	}
    60  	call.Store(&pid)
    61  	return pid, nil
    62  }
    63  
    64  func nameHasOwner(conn *dbus.Conn, sender dbus.Sender) bool {
    65  	call := conn.BusObject().Call("org.freedesktop.DBus.NameHasOwner", 0, sender)
    66  	if call.Err != nil {
    67  		return false
    68  	}
    69  	var hasOwner bool
    70  	call.Store(&hasOwner)
    71  	return hasOwner
    72  }
    73  
    74  // FIXME: move to osutil?
    75  func snapFromPid(pid int) (string, error) {
    76  	f, err := os.Open(fmt.Sprintf("%s/proc/%d/cgroup", dirs.GlobalRootDir, pid))
    77  	if err != nil {
    78  		return "", err
    79  	}
    80  	defer f.Close()
    81  
    82  	scanner := bufio.NewScanner(f)
    83  	for scanner.Scan() {
    84  		// we need to find a string like:
    85  		//   ...
    86  		//   7:freezer:/snap.hello-world
    87  		//   ...
    88  		// See cgroup(7) for details about the /proc/[pid]/cgroup
    89  		// format.
    90  		l := strings.Split(scanner.Text(), ":")
    91  		if len(l) < 3 {
    92  			continue
    93  		}
    94  		controllerList := l[1]
    95  		cgroupPath := l[2]
    96  		if !strings.Contains(controllerList, "freezer") {
    97  			continue
    98  		}
    99  		if strings.HasPrefix(cgroupPath, "/snap.") {
   100  			snap := strings.SplitN(filepath.Base(cgroupPath), ".", 2)[1]
   101  			return snap, nil
   102  		}
   103  	}
   104  	if scanner.Err() != nil {
   105  		return "", scanner.Err()
   106  	}
   107  
   108  	return "", fmt.Errorf("cannot find a snap for pid %v", pid)
   109  }