fix(storage): unescape /proc/self/mountinfo paths in getMountInfo

pkg/unikontainers/block.go

@@ -15,7 +15,6 @@
 package unikontainers
 
 import (
-	"bufio"
 	"errors"
 	"fmt"
 	"os"
@@ -56,55 +55,50 @@ type blockRootfs struct {
 // There are cases (e.g. bind mounts) where mounts use the same underlying
 // source device as the original mount, so they can appear identical to
 // regular mounts when inspecting mount information.
+//
+// We rely on moby/sys/mountinfo to parse /proc/self/mountinfo instead of
+// splitting the raw lines ourselves, because the kernel octal-escapes
+// spaces, tabs, newlines and backslashes in the root and mount point
+// fields (see proc(5)), and mountinfo.GetMounts() already decodes them.
 func getMountInfo(path string) (types.BlockDevParams, error) {
-	selfProcMountInfo := "/proc/self/mountinfo"
-
-	file, err := os.Open(selfProcMountInfo)
+	mounts, err := mountinfo.GetMounts(nil)
 	if err != nil {
-		return types.BlockDevParams{}, fmt.Errorf("failed to open mountinfo: %w", err)
+		return types.BlockDevParams{}, fmt.Errorf("failed to read mountinfo: %w", err)
 	}
-	defer file.Close()
 
+	return findMountInfo(mounts, path)
+}
+
+// findMountInfo scans already-parsed mountinfo entries for the one mounted
+// at path. It is split out from getMountInfo so the matching logic can be
+// unit tested against synthetic mounts, without depending on the real
+// /proc/self/mountinfo of the process running the test.
+func findMountInfo(mounts []*mountinfo.Info, path string) (types.BlockDevParams, error) {
 	blockDev := types.BlockDevParams{}
 	nonSpecialSources := make(map[string]struct{})
-	scanner := bufio.NewScanner(file)
-
-	for scanner.Scan() {
-		line := scanner.Text()
-		parts := strings.Split(line, " - ")
-		if len(parts) != 2 {
-			return types.BlockDevParams{}, fmt.Errorf("invalid mountinfo line in /proc/self/mountinfo")
-		}
 
-		preDash := strings.Fields(parts[0])
-		if len(preDash) < 6 {
-			continue
-		}
-		postDash := strings.Fields(parts[1])
-		if len(postDash) < 2 {
-			continue
-		}
-		if preDash[4] == path {
+	for _, m := range mounts {
+		if m.Mountpoint == path {
 			uniklog.WithFields(logrus.Fields{
 				"mounted at": path,
-				"device":     postDash[1],
-				"fstype":     postDash[0],
-				"options":    preDash[5],
+				"device":     m.Source,
+				"fstype":     m.FSType,
+				"options":    m.Options,
 			}).Debug("Found block device")
 
-			blockDev.Source = postDash[1]
-			blockDev.FsType = postDash[0]
+			blockDev.Source = m.Source
+			blockDev.FsType = m.FSType
 			blockDev.MountPoint = path
-			// Keep the-mount VFS options (field 6 of mountinfo)
+			// Keep the mount VFS options (field 6 of mountinfo)
 			// to restore them later in the delete path.
-			blockDev.MountOptions = preDash[5]
+			blockDev.MountOptions = m.Options
 			blockDev.ID = ""
 			continue
 		}
 		// Store the source of all mounts with non-special fs
 		// (e.g. overlay, tmpfs) in a map
-		if postDash[0] != postDash[1] {
-			nonSpecialSources[postDash[1]] = struct{}{}
+		if m.FSType != m.Source {
+			nonSpecialSources[m.Source] = struct{}{}
 		}
 	}
 

pkg/unikontainers/block_test.go

@@ -15,8 +15,10 @@
 package unikontainers
 
 import (
+	"strings"
 	"testing"
 
+	"github.com/moby/sys/mountinfo"
 	"github.com/stretchr/testify/assert"
 	"github.com/urunc-dev/urunc/pkg/unikontainers/types"
 )
@@ -37,3 +39,34 @@ func TestGetBlockDevice(t *testing.T) {
 	assert.Equal(t, tmpMnt.FsType, rootFs.FsType, "Expected filesystem type to be proc")
 	assert.Equal(t, tmpMnt.ID, rootFs.ID, "Expected ID to be empty")
 }
+
+// TestFindMountInfoEscapedPath reproduces a bind mount whose source path
+// contains a space, tab, newline or backslash. The kernel octal-escapes
+// these characters in /proc/self/mountinfo (e.g. a space becomes \040), so
+// this exercises that findMountInfo still matches the real, unescaped path
+// against the mountinfo entry once it has been parsed by mountinfo.GetMountsFromReader.
+func TestFindMountInfoEscapedPath(t *testing.T) {
+	tests := []struct {
+		name       string
+		path       string
+		escapedRaw string
+	}{
+		{name: "space", path: "/mnt/my volume", escapedRaw: `/mnt/my\040volume`},
+		{name: "tab", path: "/mnt/my\tvolume", escapedRaw: `/mnt/my\011volume`},
+		{name: "backslash", path: `/mnt/my\volume`, escapedRaw: `/mnt/my\134volume`},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			line := "36 35 8:1 / " + tt.escapedRaw + " rw,relatime shared:1 - ext4 /dev/sdb1 rw"
+			mounts, err := mountinfo.GetMountsFromReader(strings.NewReader(line), nil)
+			assert.NoError(t, err, "expected the synthetic mountinfo line to parse")
+
+			blockDev, err := findMountInfo(mounts, tt.path)
+			assert.NoError(t, err, "expected the escaped mount point to match the real path")
+			assert.Equal(t, "/dev/sdb1", blockDev.Source)
+			assert.Equal(t, "ext4", blockDev.FsType)
+			assert.Equal(t, tt.path, blockDev.MountPoint)
+		})
+	}
+}