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>

diff --git a/kernel/exit.c b/kernel/exit.c
index ee607720ae587490d0987ce27b62161b26c71226..dee8b4d6340317f830725759eab2fab65a0ac537 100644 (file)
--- 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,