Use Libpod tmpdir for pause path

Previously, we always computed pause path from the Rootless
runtime directory. Problem: this does not match the behavior of
Libpod when the directory changes. Libpod will continue to use
the previous directory, cached in the database; Pause pidfiles
will swap to the new path. This is problematic when the directory
needs to exist to write the pidfile, and Libpod is what creates
the directory.

There are two potential solutions - allow the pause pidfile to
move and just make the directory when we want to write it, or use
the cached Libpod paths for a guaranteed location. This patch
does the second, because it seems safer - we will never miss a
previously-existing pidfile because the location is now
consistent.

Fixes #8539

Signed-off-by: Matthew Heon <mheon@redhat.com>

7 files changed, 46 insertions, 11 deletions

diff --git a/libpod/reset.go b/libpod/reset.go
index f8828fed4..6d2842723 100644
--- a/libpod/reset.go
+++ b/libpod/reset.go
@@ -46,7 +46,7 @@ func (r *Runtime) Reset(ctx context.Context) error {
 		}
 	}
 
-	if err := stopPauseProcess(); err != nil {
+	if err := r.stopPauseProcess(); err != nil {
 		logrus.Errorf("Error stopping pause process: %v", err)
 	}
 
diff --git a/libpod/runtime.go b/libpod/runtime.go
index 73d73fb5d..1f50f3407 100644
--- a/libpod/runtime.go
+++ b/libpod/runtime.go
@@ -472,7 +472,7 @@ func makeRuntime(ctx context.Context, runtime *Runtime) (retErr error) {
 		// we will need to access the storage.
 		if os.Geteuid() != 0 {
 			aliveLock.Unlock() // Unlock to avoid deadlock as BecomeRootInUserNS will reexec.
-			pausePid, err := util.GetRootlessPauseProcessPidPath()
+			pausePid, err := util.GetRootlessPauseProcessPidPathGivenDir(runtime.config.Engine.TmpDir)
 			if err != nil {
 				return errors.Wrapf(err, "could not get pause process pid file path")
 			}
@@ -538,6 +538,15 @@ func makeRuntime(ctx context.Context, runtime *Runtime) (retErr error) {
 	return nil
 }
 
+// TmpDir gets the current Libpod temporary files directory.
+func (r *Runtime) TmpDir() (string, error) {
+	if !r.valid {
+		return "", define.ErrRuntimeStopped
+	}
+
+	return r.config.Engine.TmpDir, nil
+}
+
 // GetConfig returns a copy of the configuration used by the runtime
 func (r *Runtime) GetConfig() (*config.Config, error) {
 	r.lock.RLock()
diff --git a/libpod/runtime_migrate.go b/libpod/runtime_migrate.go
index 1ad32fe9c..f0f800ef0 100644
--- a/libpod/runtime_migrate.go
+++ b/libpod/runtime_migrate.go
@@ -18,9 +18,9 @@ import (
 	"github.com/sirupsen/logrus"
 )
 
-func stopPauseProcess() error {
+func (r *Runtime) stopPauseProcess() error {
 	if rootless.IsRootless() {
-		pausePidPath, err := util.GetRootlessPauseProcessPidPath()
+		pausePidPath, err := util.GetRootlessPauseProcessPidPathGivenDir(r.config.Engine.TmpDir)
 		if err != nil {
 			return errors.Wrapf(err, "could not get pause process pid file path")
 		}
@@ -98,5 +98,5 @@ func (r *Runtime) migrate(ctx context.Context) error {
 		}
 	}
 
-	return stopPauseProcess()
+	return r.stopPauseProcess()
 }
diff --git a/libpod/runtime_migrate_unsupported.go b/libpod/runtime_migrate_unsupported.go
index e362cca63..a9d351318 100644
--- a/libpod/runtime_migrate_unsupported.go
+++ b/libpod/runtime_migrate_unsupported.go
@@ -10,6 +10,6 @@ func (r *Runtime) migrate(ctx context.Context) error {
 	return nil
 }
 
-func stopPauseProcess() error {
+func (r *Runtime) stopPauseProcess() error {
 	return nil
 }
diff --git a/pkg/domain/infra/abi/system.go b/pkg/domain/infra/abi/system.go
index 72fd98ac1..ec2532bea 100644
--- a/pkg/domain/infra/abi/system.go
+++ b/pkg/domain/infra/abi/system.go
@@ -11,6 +11,7 @@ import (
 	"strings"
 
 	"github.com/containers/common/pkg/config"
+	"github.com/containers/podman/v2/libpod"
 	"github.com/containers/podman/v2/libpod/define"
 	"github.com/containers/podman/v2/pkg/cgroups"
 	"github.com/containers/podman/v2/pkg/domain/entities"
@@ -86,7 +87,11 @@ func (ic *ContainerEngine) SetupRootless(_ context.Context, cmd *cobra.Command)
 		return nil
 	}
 
-	pausePidPath, err := util.GetRootlessPauseProcessPidPath()
+	tmpDir, err := ic.Libpod.TmpDir()
+	if err != nil {
+		return err
+	}
+	pausePidPath, err := util.GetRootlessPauseProcessPidPathGivenDir(tmpDir)
 	if err != nil {
 		return errors.Wrapf(err, "could not get pause process pid file path")
 	}
@@ -112,7 +117,7 @@ func (ic *ContainerEngine) SetupRootless(_ context.Context, cmd *cobra.Command)
 	}
 
 	became, ret, err = rootless.TryJoinFromFilePaths(pausePidPath, true, paths)
-	if err := movePauseProcessToScope(); err != nil {
+	if err := movePauseProcessToScope(ic.Libpod); err != nil {
 		conf, err := ic.Config(context.Background())
 		if err != nil {
 			return err
@@ -133,8 +138,12 @@ func (ic *ContainerEngine) SetupRootless(_ context.Context, cmd *cobra.Command)
 	return nil
 }
 
-func movePauseProcessToScope() error {
-	pausePidPath, err := util.GetRootlessPauseProcessPidPath()
+func movePauseProcessToScope(r *libpod.Runtime) error {
+	tmpDir, err := r.TmpDir()
+	if err != nil {
+		return err
+	}
+	pausePidPath, err := util.GetRootlessPauseProcessPidPathGivenDir(tmpDir)
 	if err != nil {
 		return errors.Wrapf(err, "could not get pause process pid file path")
 	}
diff --git a/pkg/util/utils_supported.go b/pkg/util/utils_supported.go
index 2d636a7cb..a63c76415 100644
--- a/pkg/util/utils_supported.go
+++ b/pkg/util/utils_supported.go
@@ -99,7 +99,8 @@ func GetRootlessConfigHomeDir() (string, error) {
 }
 
 // GetRootlessPauseProcessPidPath returns the path to the file that holds the pid for
-// the pause process
+// the pause process.
+// DEPRECATED - switch to GetRootlessPauseProcessPidPathGivenDir
 func GetRootlessPauseProcessPidPath() (string, error) {
 	runtimeDir, err := GetRuntimeDir()
 	if err != nil {
@@ -107,3 +108,13 @@ func GetRootlessPauseProcessPidPath() (string, error) {
 	}
 	return filepath.Join(runtimeDir, "libpod", "pause.pid"), nil
 }
+
+// GetRootlessPauseProcessPidPathGivenDir returns the path to the file that
+// holds the PID of the pause process, given the location of Libpod's temporary
+// files.
+func GetRootlessPauseProcessPidPathGivenDir(libpodTmpDir string) (string, error) {
+	if libpodTmpDir == "" {
+		return "", errors.Errorf("must provide non-empty tmporary directory")
+	}
+	return filepath.Join(libpodTmpDir, "pause.pid"), nil
+}
diff --git a/pkg/util/utils_windows.go b/pkg/util/utils_windows.go
index 9bba2d1ee..46ca5e7f1 100644
--- a/pkg/util/utils_windows.go
+++ b/pkg/util/utils_windows.go
@@ -25,6 +25,12 @@ func GetRootlessPauseProcessPidPath() (string, error) {
 	return "", errors.Wrap(errNotImplemented, "GetRootlessPauseProcessPidPath")
 }
 
+// GetRootlessPauseProcessPidPath returns the path to the file that holds the pid for
+// the pause process
+func GetRootlessPauseProcessPidPathGivenDir(unused string) (string, error) {
+	return "", errors.Wrap(errNotImplemented, "GetRootlessPauseProcessPidPath")
+}
+
 // GetRuntimeDir returns the runtime directory
 func GetRuntimeDir() (string, error) {
 	return "", errors.New("this function is not implemented for windows")