diff options
author | Sebastian Andrzej Siewior <bigeasy@linutronix.de> | 2013-08-29 18:21:04 +0200 |
---|---|---|
committer | Sebastian Andrzej Siewior <bigeasy@linutronix.de> | 2016-02-13 00:36:09 +0100 |
commit | 3be37437a03fc3140fb1178f4b47ea400e77f2f1 (patch) | |
tree | 88cd8f7ee2b6af78d8cc4e48fb18f6aec56ec300 | |
parent | 760678d60a7e808210ea17a7aa35424cdcbca360 (diff) | |
download | rt-linux-3be37437a03fc3140fb1178f4b47ea400e77f2f1.tar.gz |
ptrace: fix ptrace vs tasklist_lock race
As explained by Alexander Fyodorov <halcy@yandex.ru>:
|read_lock(&tasklist_lock) in ptrace_stop() is converted to mutex on RT kernel,
|and it can remove __TASK_TRACED from task->state (by moving it to
|task->saved_state). If parent does wait() on child followed by a sys_ptrace
|call, the following race can happen:
|
|- child sets __TASK_TRACED in ptrace_stop()
|- parent does wait() which eventually calls wait_task_stopped() and returns
| child's pid
|- child blocks on read_lock(&tasklist_lock) in ptrace_stop() and moves
| __TASK_TRACED flag to saved_state
|- parent calls sys_ptrace, which calls ptrace_check_attach() and wait_task_inactive()
The patch is based on his initial patch where an additional check is
added in case the __TASK_TRACED moved to ->saved_state. The pi_lock is
taken in case the caller is interrupted between looking into ->state and
->saved_state.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
-rw-r--r-- | include/linux/sched.h | 48 | ||||
-rw-r--r-- | kernel/ptrace.c | 7 | ||||
-rw-r--r-- | kernel/sched/core.c | 17 |
3 files changed, 66 insertions, 6 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h index 0532076680ff05..d25e6400368929 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -242,10 +242,7 @@ extern char ___assert_task_state[1 - 2*!!( TASK_UNINTERRUPTIBLE | __TASK_STOPPED | \ __TASK_TRACED | EXIT_ZOMBIE | EXIT_DEAD) -#define task_is_traced(task) ((task->state & __TASK_TRACED) != 0) #define task_is_stopped(task) ((task->state & __TASK_STOPPED) != 0) -#define task_is_stopped_or_traced(task) \ - ((task->state & (__TASK_STOPPED | __TASK_TRACED)) != 0) #define task_contributes_to_load(task) \ ((task->state & TASK_UNINTERRUPTIBLE) != 0 && \ (task->flags & PF_FROZEN) == 0 && \ @@ -2984,6 +2981,51 @@ static inline int signal_pending_state(long state, struct task_struct *p) return (state & TASK_INTERRUPTIBLE) || __fatal_signal_pending(p); } +static inline bool __task_is_stopped_or_traced(struct task_struct *task) +{ + if (task->state & (__TASK_STOPPED | __TASK_TRACED)) + return true; +#ifdef CONFIG_PREEMPT_RT_FULL + if (task->saved_state & (__TASK_STOPPED | __TASK_TRACED)) + return true; +#endif + return false; +} + +static inline bool task_is_stopped_or_traced(struct task_struct *task) +{ + bool traced_stopped; + +#ifdef CONFIG_PREEMPT_RT_FULL + unsigned long flags; + + raw_spin_lock_irqsave(&task->pi_lock, flags); + traced_stopped = __task_is_stopped_or_traced(task); + raw_spin_unlock_irqrestore(&task->pi_lock, flags); +#else + traced_stopped = __task_is_stopped_or_traced(task); +#endif + return traced_stopped; +} + +static inline bool task_is_traced(struct task_struct *task) +{ + bool traced = false; + + if (task->state & __TASK_TRACED) + return true; +#ifdef CONFIG_PREEMPT_RT_FULL + /* in case the task is sleeping on tasklist_lock */ + raw_spin_lock_irq(&task->pi_lock); + if (task->state & __TASK_TRACED) + traced = true; + else if (task->saved_state & __TASK_TRACED) + traced = true; + raw_spin_unlock_irq(&task->pi_lock); +#endif + return traced; +} + /* * cond_resched() and cond_resched_lock(): latency reduction via * explicit rescheduling in places that are safe. The return diff --git a/kernel/ptrace.c b/kernel/ptrace.c index b760bae64cf123..d1d158005ad066 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -129,7 +129,12 @@ static bool ptrace_freeze_traced(struct task_struct *task) spin_lock_irq(&task->sighand->siglock); if (task_is_traced(task) && !__fatal_signal_pending(task)) { - task->state = __TASK_TRACED; + raw_spin_lock_irq(&task->pi_lock); + if (task->state & __TASK_TRACED) + task->state = __TASK_TRACED; + else + task->saved_state = __TASK_TRACED; + raw_spin_unlock_irq(&task->pi_lock); ret = true; } spin_unlock_irq(&task->sighand->siglock); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index eb3e35657e39db..8a824e155551c5 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1426,6 +1426,18 @@ out: return ret; } +static bool check_task_state(struct task_struct *p, long match_state) +{ + bool match = false; + + raw_spin_lock_irq(&p->pi_lock); + if (p->state == match_state || p->saved_state == match_state) + match = true; + raw_spin_unlock_irq(&p->pi_lock); + + return match; +} + /* * wait_task_inactive - wait for a thread to unschedule. * @@ -1470,7 +1482,7 @@ unsigned long wait_task_inactive(struct task_struct *p, long match_state) * is actually now running somewhere else! */ while (task_running(rq, p)) { - if (match_state && unlikely(p->state != match_state)) + if (match_state && !check_task_state(p, match_state)) return 0; cpu_relax(); } @@ -1485,7 +1497,8 @@ unsigned long wait_task_inactive(struct task_struct *p, long match_state) running = task_running(rq, p); queued = task_on_rq_queued(p); ncsw = 0; - if (!match_state || p->state == match_state) + if (!match_state || p->state == match_state || + p->saved_state == match_state) ncsw = p->nvcsw | LONG_MIN; /* sets MSB */ task_rq_unlock(rq, p, &flags); |