Merge release-20210816.0-52-gf7281c6cb (automated)

3 files changed, 16 insertions, 3 deletions

diff --git a/pkg/sentry/kernel/task_exec.go b/pkg/sentry/kernel/task_exec.go
index 9175b911c..db91fc4d8 100644
--- a/pkg/sentry/kernel/task_exec.go
+++ b/pkg/sentry/kernel/task_exec.go
@@ -222,9 +222,15 @@ func (r *runSyscallAfterExecStop) execute(t *Task) taskRunState {
 	// Update credentials to reflect the execve. This should precede switching
 	// MMs to ensure that dumpability has been reset first, if needed.
 	t.updateCredsForExecLocked()
-	t.image.release()
+	oldImage := t.image
 	t.image = *r.image
 	t.mu.Unlock()
+
+	// Don't hold t.mu while calling t.image.release(), that may
+	// attempt to acquire TaskImage.MemoryManager.mappingMu, a lock order
+	// violation.
+	oldImage.release()
+
 	t.unstopVforkParent()
 	t.p.FullStateChanged()
 	// NOTE(b/30316266): All locks must be dropped prior to calling Activate.
diff --git a/pkg/sentry/kernel/task_exit.go b/pkg/sentry/kernel/task_exit.go
index 342e5debe..b3931445b 100644
--- a/pkg/sentry/kernel/task_exit.go
+++ b/pkg/sentry/kernel/task_exit.go
@@ -230,9 +230,16 @@ func (*runExitMain) execute(t *Task) taskRunState {
 	t.tg.pidns.owner.mu.Lock()
 	t.updateRSSLocked()
 	t.tg.pidns.owner.mu.Unlock()
+
+	// Release the task image resources. Accessing these fields must be
+	// done with t.mu held, but the mm.DecUsers() call must be done outside
+	// of that lock.
 	t.mu.Lock()
-	t.image.release()
+	mm := t.image.MemoryManager
+	t.image.MemoryManager = nil
+	t.image.fu = nil
 	t.mu.Unlock()
+	mm.DecUsers(t)
 
 	// Releasing the MM unblocks a blocked CLONE_VFORK parent.
 	t.unstopVforkParent()
diff --git a/pkg/sentry/kernel/task_image.go b/pkg/sentry/kernel/task_image.go
index c132c27ef..6002ffb42 100644
--- a/pkg/sentry/kernel/task_image.go
+++ b/pkg/sentry/kernel/task_image.go
@@ -53,7 +53,7 @@ type TaskImage struct {
 }
 
 // release releases all resources held by the TaskImage. release is called by
-// the task when it execs into a new TaskImage or exits.
+// the task when it execs into a new TaskImage.
 func (image *TaskImage) release() {
 	// Nil out pointers so that if the task is saved after release, it doesn't
 	// follow the pointers to possibly now-invalid objects.