ptrace: Move setting/clearing ptrace_message into ptrace_stop

Today ptrace_message is easy to overlook as it not a core part of
ptrace_stop.  It has been overlooked so much that there are places
that set ptrace_message and don't clear it, and places that never set
it.  So if you get an unlucky sequence of events the ptracer may be
able to read a ptrace_message that does not apply to the current
ptrace stop.

Move setting of ptrace_message into ptrace_stop so that it always gets
set before the stop, and always gets cleared after the stop.  This
prevents non-sense from being reported to userspace and makes
ptrace_message more visible in the ptrace helper functions so that
kernel developers can see it.

Link: https://lkml.kernel.org/r/87bky67qfv.fsf_-_@email.froward.int.ebiederm.org
Acked-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 3 insertions, 6 deletions

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 5310f43e4762..3e6b46e2b7be 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -60,7 +60,7 @@ extern int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned
 extern void ptrace_disable(struct task_struct *);
 extern int ptrace_request(struct task_struct *child, long request,
 			  unsigned long addr, unsigned long data);
-extern void ptrace_notify(int exit_code);
+extern void ptrace_notify(int exit_code, unsigned long message);
 extern void __ptrace_link(struct task_struct *child,
 			  struct task_struct *new_parent,
 			  const struct cred *ptracer_cred);
@@ -155,8 +155,7 @@ static inline bool ptrace_event_enabled(struct task_struct *task, int event)
 static inline void ptrace_event(int event, unsigned long message)
 {
 	if (unlikely(ptrace_event_enabled(current, event))) {
-		current->ptrace_message = message;
-		ptrace_notify((event << 8) | SIGTRAP);
+		ptrace_notify((event << 8) | SIGTRAP, message);
 	} else if (event == PTRACE_EVENT_EXEC) {
 		/* legacy EXEC report via SIGTRAP */
 		if ((current->ptrace & (PT_PTRACED|PT_SEIZED)) == PT_PTRACED)
@@ -424,8 +423,7 @@ static inline int ptrace_report_syscall(unsigned long message)
 	if (!(ptrace & PT_PTRACED))
 		return 0;
 
-	current->ptrace_message = message;
-	ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0));
+	ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0), message);
 
 	/*
 	 * this isn't the same as continuing with a signal, but it will do
@@ -437,7 +435,6 @@ static inline int ptrace_report_syscall(unsigned long message)
 		current->exit_code = 0;
 	}
 
-	current->ptrace_message = 0;
 	return fatal_signal_pending(current);
 }