CVE-2024-7558

@@ -4,9 +4,9 @@
 package context
 
 import (
+	"crypto/rand"
+	"encoding/hex"
 	"fmt"
-	"math/rand"
-	"time"
 
 	"github.com/juju/charm/v8/hooks"
 	"github.com/juju/errors"
@@ -88,9 +88,6 @@ type contextFactory struct {
 	// Callback to get relation state snapshot.
 	getRelationInfos RelationsFunc
 	relationCaches   map[int]*RelationCache
-
-	// For generating "unique" context ids.
-	rand *rand.Rand
 }
 
 // FactoryConfig contains configuration values
@@ -149,7 +146,6 @@ func NewContextFactory(config FactoryConfig) (ContextFactory, error) {
 		machineTag:       machineTag,
 		getRelationInfos: config.GetRelationInfos,
 		relationCaches:   map[int]*RelationCache{},
-		rand:             rand.New(rand.NewSource(time.Now().Unix())),
 		clock:            config.Clock,
 		zone:             zone,
 		principal:        principal,
@@ -160,8 +156,14 @@ func NewContextFactory(config FactoryConfig) (ContextFactory, error) {
 
 // newId returns a probably-unique identifier for a new context, containing the
 // supplied string.
-func (f *contextFactory) newId(name string) string {
-	return fmt.Sprintf("%s-%s-%d", f.unit.Name(), name, f.rand.Int63())
+func (f *contextFactory) newId(name string) (string, error) {
+	randomData := [16]byte{}
+	_, err := rand.Read(randomData[:])
+	if err != nil {
+		return "", fmt.Errorf("cannot generate id for hook context: %w", err)
+	}
+	randomComponent := hex.EncodeToString(randomData[:])
+	return fmt.Sprintf("%s-%s-%s", f.unit.Name(), name, randomComponent), nil
 }
 
 // coreContext creates a new context with all unspecialised fields filled in.
@@ -214,7 +216,10 @@ func (f *contextFactory) ActionContext(actionData *ActionData) (*HookContext, er
 		return nil, errors.Trace(err)
 	}
 	ctx.actionData = actionData
-	ctx.id = f.newId(actionData.Name)
+	ctx.id, err = f.newId(actionData.Name)
+	if err != nil {
+		return nil, errors.Trace(err)
+	}
 	return ctx, nil
 }
 
@@ -264,7 +269,10 @@ func (f *contextFactory) HookContext(hookInfo hook.Info) (*HookContext, error) {
 	if hookInfo.Kind == hooks.PreSeriesUpgrade {
 		ctx.seriesUpgradeTarget = hookInfo.SeriesUpgradeTarget
 	}
-	ctx.id = f.newId(hookName)
+	ctx.id, err = f.newId(hookName)
+	if err != nil {
+		return nil, errors.Trace(err)
+	}
 	ctx.hookName = hookName
 	return ctx, nil
 }
@@ -282,7 +290,10 @@ func (f *contextFactory) CommandContext(commandInfo CommandInfo) (*HookContext,
 	}
 	ctx.relationId = relationId
 	ctx.remoteUnitName = remoteUnitName
-	ctx.id = f.newId("run-commands")
+	ctx.id, err = f.newId("run-commands")
+	if err != nil {
+		return nil, errors.Trace(err)
+	}
 	return ctx, nil
 }
 

@@ -4,7 +4,9 @@
 package context_test
 
 import (
+	"encoding/hex"
 	"os"
+	"strings"
 	"time"
 
 	"github.com/juju/charm/v8/hooks"
@@ -193,6 +195,21 @@ func (s *ContextFactorySuite) TestNewActionContextLeadershipContext(c *gc.C) {
 	})
 }
 
+func (s *ContextFactorySuite) TestHookContextID(c *gc.C) {
+	hi := hook.Info{
+		Kind: hooks.Install,
+	}
+	ctx, err := s.factory.HookContext(hi)
+	c.Assert(err, jc.ErrorIsNil)
+
+	v := strings.Split(ctx.Id(), "-")
+	c.Assert(v, gc.HasLen, 3)
+
+	randomComponent, err := hex.DecodeString(v[2])
+	c.Assert(err, jc.ErrorIsNil)
+	c.Assert(randomComponent, gc.HasLen, 16)
+}
+
 func (s *ContextFactorySuite) TestRelationHookContext(c *gc.C) {
 	hi := hook.Info{
 		Kind:       hooks.RelationBroken,