From 09e1f3c5e03322500e7b6e04fdc7c07d262ad3e7 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Tue, 3 Nov 2020 12:39:01 +0100
Subject: [PATCH 504/518] ptrace: fix ptrace_unfreeze_traced() race with
 rt-lock

The patch "ptrace: fix ptrace vs tasklist_lock race" changed
ptrace_freeze_traced() to take task->saved_state into account, but
ptrace_unfreeze_traced() has the same problem and needs a similar fix:
it should check/update both ->state and ->saved_state.

Reported-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Fixes: "ptrace: fix ptrace vs tasklist_lock race"
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: stable-rt@vger.kernel.org
(cherry picked from commit 0fdc91971b34cf6857b4cfd8c322ae936cfc189b)
Signed-off-by: Clark Williams <williams@redhat.com>
---
 kernel/ptrace.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 8b547c394e7be..cd5848f528a9e 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -207,8 +207,8 @@ static bool ptrace_freeze_traced(struct task_struct *task)
 
 static void ptrace_unfreeze_traced(struct task_struct *task)
 {
-	if (task->state != __TASK_TRACED)
-		return;
+	unsigned long flags;
+	bool frozen = true;
 
 	WARN_ON(!task->ptrace || task->parent != current);
 
@@ -217,12 +217,19 @@ static void ptrace_unfreeze_traced(struct task_struct *task)
 	 * Recheck state under the lock to close this race.
 	 */
 	spin_lock_irq(&task->sighand->siglock);
-	if (task->state == __TASK_TRACED) {
-		if (__fatal_signal_pending(task))
-			wake_up_state(task, __TASK_TRACED);
-		else
-			task->state = TASK_TRACED;
-	}
+
+	raw_spin_lock_irqsave(&task->pi_lock, flags);
+	if (task->state == __TASK_TRACED)
+		task->state = TASK_TRACED;
+	else if (task->saved_state == __TASK_TRACED)
+		task->saved_state = TASK_TRACED;
+	else
+		frozen = false;
+	raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+
+	if (frozen && __fatal_signal_pending(task))
+		wake_up_state(task, __TASK_TRACED);
+
 	spin_unlock_irq(&task->sighand->siglock);
 }
 
-- 
2.41.0

