[PATCH] coredump: kill ptrace related stuff

With this patch zap_process() sets SIGNAL_GROUP_EXIT while sending SIGKILL to
the thread group.  This means that a TASK_TRACED task

	1. Will be awakened by signal_wake_up(1)

	2. Can't sleep again via ptrace_notify()

	3. Can't go to do_signal_stop() after return
	   from ptrace_stop() in get_signal_to_deliver()

So we can remove all ptrace related stuff from coredump path.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

4 files changed, 37 insertions, 32 deletions

diff --git a/fs/exec.c b/fs/exec.c
index a5c51646d1ad..b58ba7d127e0 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1368,12 +1368,14 @@ static void format_corename(char *corename, const char *pattern, long signr)
         *out_ptr = 0;
 }
 
-static void zap_process(struct task_struct *start, int *ptraced)
+static void zap_process(struct task_struct *start)
 {
         struct task_struct *t;
         unsigned long flags;
 
         spin_lock_irqsave(&start->sighand->siglock, flags);
+        start->signal->flags = SIGNAL_GROUP_EXIT;
+        start->signal->group_stop_count = 0;
 
         t = start;
         do {
@@ -1381,22 +1383,17 @@ static void zap_process(struct task_struct *start, int *ptraced)
                         t->mm->core_waiters++;
                         sigaddset(&t->pending.signal, SIGKILL);
                         signal_wake_up(t, 1);
-
-                        if (unlikely(t->ptrace) &&
-                            unlikely(t->parent->mm == t->mm))
-                                *ptraced = 1;
                 }
         } while ((t = next_thread(t)) != start);
 
         spin_unlock_irqrestore(&start->sighand->siglock, flags);
 }
 
-static void zap_threads (struct mm_struct *mm)
+static void zap_threads(struct mm_struct *mm)
 {
         struct task_struct *g, *p;
         struct task_struct *tsk = current;
         struct completion *vfork_done = tsk->vfork_done;
-        int traced = 0;
 
         /*
          * Make sure nobody is waiting for us to release the VM,
@@ -1413,29 +1410,12 @@ static void zap_threads (struct mm_struct *mm)
                 do {
                         if (p->mm) {
                                 if (p->mm == mm)
-                                        zap_process(p, &traced);
+                                        zap_process(p);
                                 break;
                         }
                 } while ((p = next_thread(p)) != g);
         }
         read_unlock(&tasklist_lock);
-
-        if (unlikely(traced)) {
-                /*
-                 * We are zapping a thread and the thread it ptraces.
-                 * If the tracee went into a ptrace stop for exit tracing,
-                 * we could deadlock since the tracer is waiting for this
-                 * coredump to finish.  Detach them so they can both die.
-                 */
-                write_lock_irq(&tasklist_lock);
-                do_each_thread(g,p) {
-                        if (mm == p->mm && p != tsk &&
-                            p->ptrace && p->parent->mm == mm) {
-                                __ptrace_detach(p, 0);
-                        }
-                } while_each_thread(g,p);
-                write_unlock_irq(&tasklist_lock);
-        }
 }
 
 static void coredump_wait(struct mm_struct *mm)
diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index ee918bc6e18c..8b2749a259dc 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -88,7 +88,6 @@ extern int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __us
 extern int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long dst, int len);
 extern int ptrace_attach(struct task_struct *tsk);
 extern int ptrace_detach(struct task_struct *, unsigned int);
-extern void __ptrace_detach(struct task_struct *, unsigned int);
 extern void ptrace_disable(struct task_struct *);
 extern int ptrace_check_attach(struct task_struct *task, int kill);
 extern int ptrace_request(struct task_struct *child, long request, long addr, long data);
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 6252d2fa2bf3..335c5b932e14 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -214,7 +214,7 @@ out:
         return retval;
 }
 
-void __ptrace_detach(struct task_struct *child, unsigned int data)
+static inline void __ptrace_detach(struct task_struct *child, unsigned int data)
 {
         child->exit_code = data;
         /* .. re-parent .. */
@@ -233,6 +233,7 @@ int ptrace_detach(struct task_struct *child, unsigned int data)
         ptrace_disable(child);
 
         write_lock_irq(&tasklist_lock);
+        /* protect against de_thread()->release_task() */
         if (child->ptrace)
                 __ptrace_detach(child, data);
         write_unlock_irq(&tasklist_lock);
diff --git a/kernel/signal.c b/kernel/signal.c
index 1b3c921737e2..52adf53929f6 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1531,6 +1531,35 @@ static void do_notify_parent_cldstop(struct task_struct *tsk, int why)
         spin_unlock_irqrestore(&sighand->siglock, flags);
 }
 
+static inline int may_ptrace_stop(void)
+{
+        if (!likely(current->ptrace & PT_PTRACED))
+                return 0;
+
+        if (unlikely(current->parent == current->real_parent &&
+                    (current->ptrace & PT_ATTACHED)))
+                return 0;
+
+        if (unlikely(current->signal == current->parent->signal) &&
+            unlikely(current->signal->flags & SIGNAL_GROUP_EXIT))
+                return 0;
+
+        /*
+         * Are we in the middle of do_coredump?
+         * If so and our tracer is also part of the coredump stopping
+         * is a deadlock situation, and pointless because our tracer
+         * is dead so don't allow us to stop.
+         * If SIGKILL was already sent before the caller unlocked
+         * ->siglock we must see ->core_waiters != 0. Otherwise it
+         * is safe to enter schedule().
+         */
+        if (unlikely(current->mm->core_waiters) &&
+            unlikely(current->mm == current->parent->mm))
+                return 0;
+
+        return 1;
+}
+
 /*
  * This must be called with current->sighand->siglock held.
  *
@@ -1559,11 +1588,7 @@ static void ptrace_stop(int exit_code, int nostop_code, siginfo_t *info)
         spin_unlock_irq(&current->sighand->siglock);
         try_to_freeze();
         read_lock(&tasklist_lock);
-        if (likely(current->ptrace & PT_PTRACED) &&
-            likely(current->parent != current->real_parent ||
-                   !(current->ptrace & PT_ATTACHED)) &&
-            (likely(current->parent->signal != current->signal) ||
-             !unlikely(current->signal->flags & SIGNAL_GROUP_EXIT))) {
+        if (may_ptrace_stop()) {
                 do_notify_parent_cldstop(current, CLD_TRAPPED);
                 read_unlock(&tasklist_lock);
                 schedule();