github.com/rigado/snapd@v2.42.5-go-mod+incompatible/cmd/snap-update-ns/common.go (about)

     1  // -*- Mode: Go; indent-tabs-mode: t -*-
     2  
     3  /*
     4   * Copyright (C) 2019 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 main
    21  
    22  import (
    23  	"fmt"
    24  
    25  	"github.com/snapcore/snapd/cmd/snaplock"
    26  	"github.com/snapcore/snapd/logger"
    27  	"github.com/snapcore/snapd/osutil"
    28  )
    29  
    30  type CommonProfileUpdateContext struct {
    31  	// instanceName is the name of the snap instance to update.
    32  	instanceName string
    33  
    34  	// fromSnapConfine indicates that the update is triggered by snap-confine
    35  	// and not from snapd. When set, snap-confine is still constructing the user
    36  	// mount namespace and is delegating mount profile application to snap-update-ns.
    37  	fromSnapConfine bool
    38  
    39  	currentProfilePath string
    40  	desiredProfilePath string
    41  }
    42  
    43  // InstanceName returns the snap instance name being updated.
    44  func (upCtx *CommonProfileUpdateContext) InstanceName() string {
    45  	return upCtx.instanceName
    46  }
    47  
    48  // Lock acquires locks / freezes needed to synchronize mount namespace changes.
    49  func (upCtx *CommonProfileUpdateContext) Lock() (func(), error) {
    50  	instanceName := upCtx.instanceName
    51  
    52  	// Lock the mount namespace so that any concurrently attempted invocations
    53  	// of snap-confine are synchronized and will see consistent state.
    54  	lock, err := snaplock.OpenLock(instanceName)
    55  	if err != nil {
    56  		return nil, fmt.Errorf("cannot open lock file for mount namespace of snap %q: %s", instanceName, err)
    57  	}
    58  
    59  	logger.Debugf("locking mount namespace of snap %q", instanceName)
    60  	if upCtx.fromSnapConfine {
    61  		// When --from-snap-confine is passed then we just ensure that the
    62  		// namespace is locked. This is used by snap-confine to use
    63  		// snap-update-ns to apply mount profiles.
    64  		if err := lock.TryLock(); err != osutil.ErrAlreadyLocked {
    65  			// If we managed to grab the lock we should drop it.
    66  			lock.Close()
    67  			return nil, fmt.Errorf("mount namespace of snap %q is not locked but --from-snap-confine was used", instanceName)
    68  		}
    69  	} else {
    70  		if err := lock.Lock(); err != nil {
    71  			return nil, fmt.Errorf("cannot lock mount namespace of snap %q: %s", instanceName, err)
    72  		}
    73  	}
    74  
    75  	// Freeze the mount namespace and unfreeze it later. This lets us perform
    76  	// modifications without snap processes attempting to construct
    77  	// symlinks or perform other malicious activity (such as attempting to
    78  	// introduce a symlink that would cause us to mount something other
    79  	// than what we expected).
    80  	logger.Debugf("freezing processes of snap %q", instanceName)
    81  	if err := freezeSnapProcesses(instanceName); err != nil {
    82  		// If we cannot freeze the processes we should drop the lock.
    83  		lock.Close()
    84  		return nil, err
    85  	}
    86  
    87  	unlock := func() {
    88  		logger.Debugf("unlocking mount namespace of snap %q", instanceName)
    89  		lock.Close()
    90  		logger.Debugf("thawing processes of snap %q", instanceName)
    91  		thawSnapProcesses(instanceName)
    92  	}
    93  	return unlock, nil
    94  }
    95  
    96  func (upCtx *CommonProfileUpdateContext) Assumptions() *Assumptions {
    97  	return nil
    98  }
    99  
   100  // LoadDesiredProfile loads the desired mount profile.
   101  func (upCtx *CommonProfileUpdateContext) LoadDesiredProfile() (*osutil.MountProfile, error) {
   102  	profile, err := osutil.LoadMountProfile(upCtx.desiredProfilePath)
   103  	if err != nil {
   104  		return nil, fmt.Errorf("cannot load desired mount profile of snap %q: %s", upCtx.instanceName, err)
   105  	}
   106  	return profile, nil
   107  }
   108  
   109  // LoadCurrentProfile loads the current mount profile.
   110  func (upCtx *CommonProfileUpdateContext) LoadCurrentProfile() (*osutil.MountProfile, error) {
   111  	profile, err := osutil.LoadMountProfile(upCtx.currentProfilePath)
   112  	if err != nil {
   113  		return nil, fmt.Errorf("cannot load current mount profile of snap %q: %s", upCtx.instanceName, err)
   114  	}
   115  	return profile, nil
   116  }
   117  
   118  // SaveCurrentProfile saves the current mount profile.
   119  func (upCtx *CommonProfileUpdateContext) SaveCurrentProfile(profile *osutil.MountProfile) error {
   120  	if err := profile.Save(upCtx.currentProfilePath); err != nil {
   121  		return fmt.Errorf("cannot save current mount profile of snap %q: %s", upCtx.instanceName, err)
   122  	}
   123  	return nil
   124  }