Handle symlinks when checking DB vs runtime configs

When Podman starts, it checks a number of critical runtime paths
against stored values in the database to make sure that existing
containers are not broken by a configuration change. We recently
made some changes to this logic to make our handling of the some
options more sane (StaticDir in particular was set based on other
passed options in a way that was not particularly sane) which has
made the logic more sensitive to paths with symlinks. As a simple
fix, handle symlinks properly in our DB vs runtime comparisons.

The BoltDB bits are uglier because very, very old Podman versions
sometimes did not stuff a proper value in the database and
instead used the empty string. SQLite is new enough that we don't
have to worry about such things.

Fixes containers#20872

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

libpod/boltdb_state_internal.go

@@ -4,7 +4,9 @@
 package libpod
 
 import (
+	"errors"
 	"fmt"
+	"io/fs"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -93,6 +95,7 @@ type dbConfigValidation struct {
 	runtimeValue string
 	key          []byte
 	defaultValue string
+	isPath       bool
 }
 
 // Check if the configuration of the database is compatible with the
@@ -111,42 +114,49 @@ func checkRuntimeConfig(db *bolt.DB, rt *Runtime) error {
 			runtime.GOOS,
 			osKey,
 			runtime.GOOS,
+			false,
 		},
 		{
 			"libpod root directory (staticdir)",
 			filepath.Clean(rt.config.Engine.StaticDir),
 			staticDirKey,
 			"",
+			true,
 		},
 		{
 			"libpod temporary files directory (tmpdir)",
 			filepath.Clean(rt.config.Engine.TmpDir),
 			tmpDirKey,
 			"",
+			true,
 		},
 		{
 			"storage temporary directory (runroot)",
 			filepath.Clean(rt.StorageConfig().RunRoot),
 			runRootKey,
 			storeOpts.RunRoot,
+			true,
 		},
 		{
 			"storage graph root directory (graphroot)",
 			filepath.Clean(rt.StorageConfig().GraphRoot),
 			graphRootKey,
 			storeOpts.GraphRoot,
+			true,
 		},
 		{
 			"storage graph driver",
 			rt.StorageConfig().GraphDriverName,
 			graphDriverKey,
 			storeOpts.GraphDriverName,
+			false,
 		},
 		{
 			"volume path",
 			rt.config.Engine.VolumePath,
 			volPathKey,
 			"",
+			true,
 		},
 	}
 
@@ -221,22 +231,45 @@ func readOnlyValidateConfig(bucket *bolt.Bucket, toCheck dbConfigValidation) (bo
 	}
 
 	dbValue := string(keyBytes)
+	ourValue := toCheck.runtimeValue
+
+	// Tolerate symlinks when possible - most relevant for OStree systems
+	// and rootless containers, where we want to put containers in /home,
+	// which is symlinked to /var/home.
+	if toCheck.isPath {
+		if dbValue != "" {
+			// Ignore ENOENT on both, on a fresh system some paths
+			// may not exist this early in Libpod init.
+			dbVal, err := filepath.EvalSymlinks(dbValue)
+			if err != nil && !errors.Is(err, fs.ErrNotExist) {
+				return false, fmt.Errorf("evaluating symlinks on DB %s path %q: %w", toCheck.name, dbValue, err)
+			}
+			dbValue = dbVal
+		}
+		if ourValue != "" {
+			ourVal, err := filepath.EvalSymlinks(ourValue)
+			if err != nil && !errors.Is(err, fs.ErrNotExist) {
+				return false, fmt.Errorf("evaluating symlinks on configured %s path %q: %w", toCheck.name, ourValue, err)
+			}
+			ourValue = ourVal
+		}
+	}
 
-	if toCheck.runtimeValue != dbValue {
+	if ourValue != dbValue {
 		// If the runtime value is the empty string and default is not,
 		// check against default.
-		if toCheck.runtimeValue == "" && toCheck.defaultValue != "" && dbValue == toCheck.defaultValue {
+		if ourValue == "" && toCheck.defaultValue != "" && dbValue == toCheck.defaultValue {
 			return true, nil
 		}
 
 		// If the DB value is the empty string, check that the runtime
 		// value is the default.
-		if dbValue == "" && toCheck.defaultValue != "" && toCheck.runtimeValue == toCheck.defaultValue {
+		if dbValue == "" && toCheck.defaultValue != "" && ourValue == toCheck.defaultValue {
 			return true, nil
 		}
 
 		return true, fmt.Errorf("database %s %q does not match our %s %q: %w",
-			toCheck.name, dbValue, toCheck.name, toCheck.runtimeValue, define.ErrDBBadConfig)
+			toCheck.name, dbValue, toCheck.name, ourValue, define.ErrDBBadConfig)
 	}
 
 	return true, nil

libpod/sqlite_state.go

@@ -7,6 +7,7 @@ import (
 	"database/sql"
 	"errors"
 	"fmt"
+	"io/fs"
 	"os"
 	"path/filepath"
 	goruntime "runtime"
@@ -315,7 +316,7 @@ func (s *SQLiteState) ValidateDBConfig(runtime *Runtime) (defErr error) {
         );`
 
 	var (
-		os, staticDir, tmpDir, graphRoot, runRoot, graphDriver, volumePath string
+		dbOS, staticDir, tmpDir, graphRoot, runRoot, graphDriver, volumePath string
 		runtimeOS                                                          = goruntime.GOOS
 		runtimeStaticDir                                                   = filepath.Clean(s.runtime.config.Engine.StaticDir)
 		runtimeTmpDir                                                      = filepath.Clean(s.runtime.config.Engine.TmpDir)
@@ -359,7 +360,7 @@ func (s *SQLiteState) ValidateDBConfig(runtime *Runtime) (defErr error) {
 
 	row := tx.QueryRow("SELECT Os, StaticDir, TmpDir, GraphRoot, RunRoot, GraphDriver, VolumeDir FROM DBConfig;")
 
-	if err := row.Scan(&os, &staticDir, &tmpDir, &graphRoot, &runRoot, &graphDriver, &volumePath); err != nil {
+	if err := row.Scan(&dbOS, &staticDir, &tmpDir, &graphRoot, &runRoot, &graphDriver, &volumePath); err != nil {
 		if errors.Is(err, sql.ErrNoRows) {
 			if _, err := tx.Exec(createRow, 1, schemaVersion, runtimeOS,
 				runtimeStaticDir, runtimeTmpDir, runtimeGraphRoot,
@@ -377,33 +378,47 @@ func (s *SQLiteState) ValidateDBConfig(runtime *Runtime) (defErr error) {
 		return fmt.Errorf("retrieving DB config: %w", err)
 	}
 
-	checkField := func(fieldName, dbVal, ourVal string) error {
+	checkField := func(fieldName, dbVal, ourVal string, isPath bool) error {
+		if isPath {
+			// Evaluate symlinks. Ignore ENOENT.
+			dbValClean, err := filepath.EvalSymlinks(dbVal)
+			if err != nil && !errors.Is(err, fs.ErrNotExist) {
+				return fmt.Errorf("cannot evaluate symlinks on DB %s path %q: %w", fieldName, dbVal, err)
+			}
+			dbVal = dbValClean
+			ourValClean, err := filepath.EvalSymlinks(dbVal)
+			if err != nil && !errors.Is(err, fs.ErrNotExist) {
+				return fmt.Errorf("cannot evaluate symlinks on our %s path %q: %w", fieldName, ourVal, err)
+			}
+			ourVal = ourValClean
+		}
+
 		if dbVal != ourVal {
 			return fmt.Errorf("database %s %q does not match our %s %q: %w", fieldName, dbVal, fieldName, ourVal, define.ErrDBBadConfig)
 		}
 
 		return nil
 	}
 
-	if err := checkField("os", os, runtimeOS); err != nil {
+	if err := checkField("os", dbOS, runtimeOS, false); err != nil {
 		return err
 	}
-	if err := checkField("static dir", staticDir, runtimeStaticDir); err != nil {
+	if err := checkField("static dir", staticDir, runtimeStaticDir, true); err != nil {
 		return err
 	}
-	if err := checkField("tmp dir", tmpDir, runtimeTmpDir); err != nil {
+	if err := checkField("tmp dir", tmpDir, runtimeTmpDir, true); err != nil {
 		return err
 	}
-	if err := checkField("graph root", graphRoot, runtimeGraphRoot); err != nil {
+	if err := checkField("graph root", graphRoot, runtimeGraphRoot, true); err != nil {
 		return err
 	}
-	if err := checkField("run root", runRoot, runtimeRunRoot); err != nil {
+	if err := checkField("run root", runRoot, runtimeRunRoot, true); err != nil {
 		return err
 	}
-	if err := checkField("graph driver", graphDriver, runtimeGraphDriver); err != nil {
+	if err := checkField("graph driver", graphDriver, runtimeGraphDriver, false); err != nil {
 		return err
 	}
-	if err := checkField("volume path", volumePath, runtimeVolumePath); err != nil {
+	if err := checkField("volume path", volumePath, runtimeVolumePath, true); err != nil {
 		return err
 	}
 

test/system/005-info.bats

@@ -187,6 +187,21 @@ host.slirp4netns.executable | $expr_path
     fi
 }
 
+@test "rootless podman with symlinked $HOME" {
+    # This is only needed as rootless, but we don't have a skip_if_root
+    # And it will not hurt to run as root.
+    skip_if_remote "path validation is only done in libpod, does not effect remote"
+
+    new_home=$PODMAN_TMPDIR/home
+
+    ln -s /home $new_home
+
+    # Just need the command to run cleanly
+    HOME=$new_home run_podman info
+
+    rm $new_home
+}
+
 @test "podman --root PATH --volumepath info - basic output" {
     volumePath=${PODMAN_TMPDIR}/volumesGoHere
     if ! is_remote; then