ptrace: implement PTRACE_LISTEN

[karo-tx-linux.git] / kernel / ptrace.c

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 6852c0f4a91691f99a2ff7911d18d76535ee52d8..e18966c1c0da4d2724e72dad79da8324a8a971ed 100644 (file)
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -146,7 +146,8 @@ int ptrace_check_attach(struct task_struct *child, bool ignore_state)
                 */
                spin_lock_irq(&child->sighand->siglock);
                WARN_ON_ONCE(task_is_stopped(child));
-               if (task_is_traced(child) || ignore_state)
+               if (ignore_state || (task_is_traced(child) &&
+                                    !(child->jobctl & JOBCTL_LISTENING)))
                        ret = 0;
                spin_unlock_irq(&child->sighand->siglock);
        }
@@ -660,7 +661,7 @@ int ptrace_request(struct task_struct *child, long request,
 {
        bool seized = child->ptrace & PT_SEIZED;
        int ret = -EIO;
-       siginfo_t siginfo;
+       siginfo_t siginfo, *si;
        void __user *datavp = (void __user *) data;
        unsigned long __user *datalp = datavp;
        unsigned long flags;
@@ -710,8 +711,43 @@ int ptrace_request(struct task_struct *child, long request,
                if (unlikely(!seized || !lock_task_sighand(child, &flags)))
                        break;
 
+               /*
+                * INTERRUPT doesn't disturb existing trap sans one
+                * exception.  If ptracer issued LISTEN for the current
+                * STOP, this INTERRUPT should clear LISTEN and re-trap
+                * tracee into STOP.
+                */
                if (likely(task_set_jobctl_pending(child, JOBCTL_TRAP_STOP)))
-                       signal_wake_up(child, 0);
+                       signal_wake_up(child, child->jobctl & JOBCTL_LISTENING);
+
+               unlock_task_sighand(child, &flags);
+               ret = 0;
+               break;
+
+       case PTRACE_LISTEN:
+               /*
+                * Listen for events.  Tracee must be in STOP.  It's not
+                * resumed per-se but is not considered to be in TRACED by
+                * wait(2) or ptrace(2).  If an async event (e.g. group
+                * stop state change) happens, tracee will enter STOP trap
+                * again.  Alternatively, ptracer can issue INTERRUPT to
+                * finish listening and re-trap tracee into STOP.
+                */
+               if (unlikely(!seized || !lock_task_sighand(child, &flags)))
+                       break;
+
+               si = child->last_siginfo;
+               if (unlikely(!si || si->si_code >> 8 != PTRACE_EVENT_STOP))
+                       break;
+
+               child->jobctl |= JOBCTL_LISTENING;
+
+               /*
+                * If NOTIFY is set, it means event happened between start
+                * of this trap and now.  Trigger re-trap immediately.
+                */
+               if (child->jobctl & JOBCTL_TRAP_NOTIFY)
+                       signal_wake_up(child, true);
 
                unlock_task_sighand(child, &flags);
                ret = 0;