wait_task_continued/zombie: don't use task_pid_nr_ns() lockless

Surprise, the other two wait_task_*() functions also abuse the
task_pid_nr_ns() function, and may cause read-after-free or report nr == 0
in wait_task_continued().  wait_task_zombie() doesn't have this problem,
but it is still better to cache pid_t rather than call task_pid_nr_ns()
three times on the saved pid_namespace.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 10 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index ee607720ae58..dee8b4d63403 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1189,12 +1189,9 @@ static int wait_task_zombie(struct task_struct *p, int noreap,
 {
         unsigned long state;
         int retval, status, traced;
-        struct pid_namespace *ns;
-
-        ns = current->nsproxy->pid_ns;
+        pid_t pid = task_pid_nr_ns(p, current->nsproxy->pid_ns);
 
         if (unlikely(noreap)) {
-                pid_t pid = task_pid_nr_ns(p, ns);
                 uid_t uid = p->uid;
                 int exit_code = p->exit_code;
                 int why, status;
@@ -1313,11 +1310,11 @@ static int wait_task_zombie(struct task_struct *p, int noreap,
                         retval = put_user(status, &infop->si_status);
         }
         if (!retval && infop)
-                retval = put_user(task_pid_nr_ns(p, ns), &infop->si_pid);
+                retval = put_user(pid, &infop->si_pid);
         if (!retval && infop)
                 retval = put_user(p->uid, &infop->si_uid);
         if (!retval)
-                retval = task_pid_nr_ns(p, ns);
+                retval = pid;
 
         if (traced) {
                 write_lock_irq(&tasklist_lock);
@@ -1436,7 +1433,6 @@ static int wait_task_continued(struct task_struct *p, int noreap,
         int retval;
         pid_t pid;
         uid_t uid;
-        struct pid_namespace *ns;
 
         if (!(p->signal->flags & SIGNAL_STOP_CONTINUED))
                 return 0;
@@ -1451,8 +1447,7 @@ static int wait_task_continued(struct task_struct *p, int noreap,
                 p->signal->flags &= ~SIGNAL_STOP_CONTINUED;
         spin_unlock_irq(&p->sighand->siglock);
 
-        ns = current->nsproxy->pid_ns;
-        pid = task_pid_nr_ns(p, ns);
+        pid = task_pid_nr_ns(p, current->nsproxy->pid_ns);
         uid = p->uid;
         get_task_struct(p);
         read_unlock(&tasklist_lock);
@@ -1463,7 +1458,7 @@ static int wait_task_continued(struct task_struct *p, int noreap,
                 if (!retval && stat_addr)
                         retval = put_user(0xffff, stat_addr);
                 if (!retval)
-                        retval = task_pid_nr_ns(p, ns);
+                        retval = pid;
         } else {
                 retval = wait_noreap_copyout(p, pid, uid,
                                              CLD_CONTINUED, SIGCONT,