libpod: fix mount order for "/" volume

The count function for / and /proc results in the same value so the
order is not guaranteed. We must ensure that a / mount is always first
in the spec so that other mounts are not overshadowed by it.

Fixes: #26161

Signed-off-by: Paul Holzinger <[email protected]>

Author: Luap99

libpod/util.go

@@ -12,7 +12,7 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
-	"sort"
+	"slices"
 	"strconv"
 	"strings"
 	"time"
@@ -46,26 +46,28 @@ func MountExists(specMounts []spec.Mount, dest string) bool {
 	return false
 }
 
-type byDestination []spec.Mount
-
-func (m byDestination) Len() int {
-	return len(m)
-}
-
-func (m byDestination) Less(i, j int) bool {
-	return m.parts(i) < m.parts(j)
-}
-
-func (m byDestination) Swap(i, j int) {
-	m[i], m[j] = m[j], m[i]
-}
-
-func (m byDestination) parts(i int) int {
-	return strings.Count(filepath.Clean(m[i].Destination), string(os.PathSeparator))
+func parts(m spec.Mount) int {
+	// We must special case a root mount /.
+	// The count of "/" and "/proc" are both 1 but of course logically "/" must
+	// be mounted before "/proc" as such set the count to 0.
+	if m.Destination == "/" {
+		return 0
+	}
+	return strings.Count(filepath.Clean(m.Destination), string(os.PathSeparator))
 }
 
 func sortMounts(m []spec.Mount) []spec.Mount {
-	sort.Sort(byDestination(m))
+	slices.SortStableFunc(m, func(a, b spec.Mount) int {
+		aLen := parts(a)
+		bLen := parts(b)
+		if aLen < bLen {
+			return -1
+		}
+		if aLen == bLen {
+			return 0
+		}
+		return 1
+	})
 	return m
 }
 

libpod/util_test.go

@@ -0,0 +1,69 @@
+//go:build !remote
+
+package libpod
+
+import (
+	"testing"
+
+	spec "github.com/opencontainers/runtime-spec/specs-go"
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_sortMounts(t *testing.T) {
+	tests := []struct {
+		name string
+		args []spec.Mount
+		want []spec.Mount
+	}{
+		{
+			name: "simple nested mounts",
+			args: []spec.Mount{
+				{
+					Destination: "/abc/123",
+				},
+				{
+					Destination: "/abc",
+				},
+			},
+			want: []spec.Mount{
+				{
+					Destination: "/abc",
+				},
+				{
+					Destination: "/abc/123",
+				},
+			},
+		},
+		{
+			name: "root mount",
+			args: []spec.Mount{
+				{
+					Destination: "/abc",
+				},
+				{
+					Destination: "/",
+				},
+				{
+					Destination: "/def",
+				},
+			},
+			want: []spec.Mount{
+				{
+					Destination: "/",
+				},
+				{
+					Destination: "/abc",
+				},
+				{
+					Destination: "/def",
+				},
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := sortMounts(tt.args)
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}