From: Oleg Nesterov Surprise, other 2 wait_task_() functions also abuse task_pid_nr_ns(). May cause read-after-free or report nr == 0 in wait_task_continued(). wait_task_zombie() doesn't have this problem, but still it is better to cache pid_t rather than call task_pid_nr_ns() 3 times on the saved pid_namespace. Signed-off-by: Oleg Nesterov Cc: Roland McGrath Signed-off-by: Andrew Morton --- kernel/exit.c | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-) diff -puN kernel/exit.c~wait_task_continued-zombie-dont-use-task_pid_nr_ns-lockless kernel/exit.c --- a/kernel/exit.c~wait_task_continued-zombie-dont-use-task_pid_nr_ns-lockless +++ a/kernel/exit.c @@ -1185,12 +1185,9 @@ static int wait_task_zombie(struct task_ { 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; @@ -1309,11 +1306,11 @@ static int wait_task_zombie(struct task_ 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); @@ -1432,7 +1429,6 @@ static int wait_task_continued(struct ta int retval; pid_t pid; uid_t uid; - struct pid_namespace *ns; if (!(p->signal->flags & SIGNAL_STOP_CONTINUED)) return 0; @@ -1447,8 +1443,7 @@ static int wait_task_continued(struct ta 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); @@ -1459,7 +1454,7 @@ static int wait_task_continued(struct ta 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, _