linux-kernel - [PATCH 48/80] tty: the vhangup syscall is racy

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Message-ID: <20081013094024.21645.47677.stgit@localhost.localdomain>
Date:	Mon, 13 Oct 2008 10:40:30 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: [PATCH 48/80] tty: the vhangup syscall is racy

From: Alan Cox <alan@...hat.com>

We now have the infrastructure to sort this out but rather than teaching
the syscall tty lock rules we move the hard work into a tty helper

Signed-off-by: Alan Cox <alan@...hat.com>
---

 drivers/char/tty_io.c |   19 +++++++++++++++++++
 fs/open.c             |    3 +--
 include/linux/tty.h   |    1 +
 3 files changed, 21 insertions(+), 2 deletions(-)


diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 913b502..b5f57d0 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -730,6 +730,25 @@ void tty_vhangup(struct tty_struct *tty)
 EXPORT_SYMBOL(tty_vhangup);
 
 /**
+ *	tty_vhangup_self	-	process vhangup for own ctty
+ *
+ *	Perform a vhangup on the current controlling tty
+ */
+
+void tty_vhangup_self(void)
+{
+	struct tty_struct *tty;
+
+	mutex_lock(&tty_mutex);
+	tty = get_current_tty();
+	if (tty) {
+		tty_vhangup(tty);
+		tty_kref_put(tty);
+	}
+	mutex_unlock(&tty_mutex);
+}
+
+/**
  *	tty_hung_up_p		-	was tty hung up
  *	@filp: file pointer of tty
  *
diff --git a/fs/open.c b/fs/open.c
index 07da935..5596049 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1141,8 +1141,7 @@ EXPORT_SYMBOL(sys_close);
 asmlinkage long sys_vhangup(void)
 {
 	if (capable(CAP_SYS_TTY_CONFIG)) {
-		/* XXX: this needs locking */
-		tty_vhangup(current->signal->tty);
+		tty_vhangup_self();
 		return 0;
 	}
 	return -EPERM;
diff --git a/include/linux/tty.h b/include/linux/tty.h
index c30ed8d..e00393a 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -361,6 +361,7 @@ extern int is_ignored(int sig);
 extern int tty_signal(int sig, struct tty_struct *tty);
 extern void tty_hangup(struct tty_struct *tty);
 extern void tty_vhangup(struct tty_struct *tty);
+extern void tty_vhangup_self(void);
 extern void tty_unhangup(struct file *filp);
 extern int tty_hung_up_p(struct file *filp);
 extern void do_SAK(struct tty_struct *tty);

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