[PATCH] ptrace-fix-2.5.34-A2, BK-curr

I distilled the attached fix-patch from Daniel's bigger patch - it
includes all fixes for all currently known ptrace related breakages,
which include things like bad behavior (crash) if the tracer process
dies unexpectedly.

kernel/exit.c

@@ -465,6 +465,7 @@ static inline void forget_original_parent(struct task_struct * father)
 	 */
 	list_for_each(_p, &father->children) {
 		p = list_entry(_p,struct task_struct,sibling);
+		if (father == p->real_parent)
 			reparent_thread(p, reaper, child_reaper);
 	}
 	list_for_each(_p, &father->ptrace_children) {
@@ -485,9 +486,16 @@ static inline void zap_thread(task_t *p, task_t *father, int traced)
 		p->ptrace = ptrace_flag;
 		__ptrace_link(p, trace_task);
 	} else {
-		/* Otherwise, if we were tracing this thread, untrace it.  */
+		/*
+		 * Otherwise, if we were tracing this thread, untrace it.
+		 * If we were only tracing the thread (i.e. not its real
+		 * parent), stop here.
+		 */
 		ptrace_unlink (p);
-
+		if (p->parent != father) {
+			BUG_ON(p->parent != p->real_parent);
+			return;
+		}
 		list_del_init(&p->sibling);
 		p->parent = p->real_parent;
 		list_add_tail(&p->sibling, &p->parent->children);

kernel/fork.c

@@ -790,6 +790,12 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	if (clone_flags & CLONE_CLEARTID)
 		p->user_tid = user_tid;
 
+	/*
+	 * Syscall tracing should be turned off in the child regardless
+	 * of CLONE_PTRACE.
+	 */
+	clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
+
 	/* Our parent execution domain becomes current domain
 	   These must match for thread signalling to apply */