linux-kernel - [PATCH v2 1/2] tty: add missing rcu_read_lock for task

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Date:	Sat, 27 Jun 2015 20:51:28 -0400
From:	Patrick Donnelly <batrick@...bytes.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	linux-kernel@...r.kernel.org (open list)
Cc:	Patrick Donnelly <batrick@...bytes.com>
Subject: [PATCH v2 1/2] tty: add missing rcu_read_lock for task_pgrp

task_pgrp requires an rcu or tasklist lock to be obtained if the returned pid
is to be dereferenced, which kill_pgrp does. Obtain an RCU lock for the
duration of use.

Signed-off-by: Patrick Donnelly <batrick@...bytes.com>
---
 drivers/tty/tty_io.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 57fc6ee..fbb55db 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -388,33 +388,39 @@ EXPORT_SYMBOL_GPL(tty_find_polling_driver);
 int tty_check_change(struct tty_struct *tty)
 {
 	unsigned long flags;
+	struct pid *pgrp;
 	int ret = 0;
 
 	if (current->signal->tty != tty)
 		return 0;
 
-	spin_lock_irqsave(&tty->ctrl_lock, flags);
+	rcu_read_lock();
+	pgrp = task_pgrp(current);
 
+	spin_lock_irqsave(&tty->ctrl_lock, flags);
 	if (!tty->pgrp) {
 		printk(KERN_WARNING "tty_check_change: tty->pgrp == NULL!\n");
-		goto out_unlock;
+		goto out_irqunlock;
 	}
-	if (task_pgrp(current) == tty->pgrp)
-		goto out_unlock;
+	if (pgrp == tty->pgrp)
+		goto out_irqunlock;
 	spin_unlock_irqrestore(&tty->ctrl_lock, flags);
+
 	if (is_ignored(SIGTTOU))
-		goto out;
+		goto out_rcuunlock;
 	if (is_current_pgrp_orphaned()) {
 		ret = -EIO;
-		goto out;
+		goto out_rcuunlock;
 	}
-	kill_pgrp(task_pgrp(current), SIGTTOU, 1);
+	kill_pgrp(pgrp, SIGTTOU, 1);
+	rcu_read_unlock();
 	set_thread_flag(TIF_SIGPENDING);
 	ret = -ERESTARTSYS;
-out:
 	return ret;
-out_unlock:
+out_irqunlock:
 	spin_unlock_irqrestore(&tty->ctrl_lock, flags);
+out_rcuunlock:
+	rcu_read_unlock();
 	return ret;
 }
 
-- 
Patrick Donnelly

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