merge #3790 into main

Kazuki Hasegawa (1):
  Fix undefined behavior. Do not accept setjmp return value as variable.

LGTMs: AkihiroSuda cyphar
Closes #3790

libcontainer/nsenter/nsexec.c

@@ -980,8 +980,7 @@ void nsexec(void)
  * -- Aleksa "what has my life come to?" Sarai
  */
 
- current_stage = setjmp(env);
- switch (current_stage) {
+ switch (setjmp(env)) {
  /*
  * Stage 0: We're in the parent. Our job is just to create a new child
  * (stage 1: STAGE_CHILD) process and write its uid_map and
@@ -995,6 +994,7 @@ void nsexec(void)
  bool stage1_complete, stage2_complete;
 
  /* For debugging. */
+ current_stage = STAGE_PARENT;
  prctl(PR_SET_NAME, (unsigned long)"runc:[0:PARENT]", 0, 0, 0);
  write_log(DEBUG, "~> nsexec stage-0");
 
@@ -1152,6 +1152,9 @@ void nsexec(void)
  pid_t stage2_pid = -1;
  enum sync_t s;
 
+ /* For debugging. */
+ current_stage = STAGE_CHILD;
+
  /* We're in a child and thus need to tell the parent if we die. */
  syncfd = sync_child_pipe[0];
  if (close(sync_child_pipe[1]) < 0)
@@ -1323,6 +1326,9 @@ void nsexec(void)
  */
  enum sync_t s;
 
+ /* For debugging. */
+ current_stage = STAGE_INIT;
+
  /* We're in a child and thus need to tell the parent if we die. */
  syncfd = sync_grandchild_pipe[0];
  if (close(sync_grandchild_pipe[1]) < 0)
@@ -1377,7 +1383,7 @@ void nsexec(void)
  }
  break;
  default:
- bail("unknown stage '%d' for jump value", current_stage);
+ bail("unexpected jump value");
  }
 
  /* Should never be reached. */