tty: the vhangup syscall is racy

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@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 21 insertions, 2 deletions

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 913b50258f90..b5f57d0b30ee 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 07da9359481c..5596049863bf 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 c30ed8d3bcbd..e00393a3d1c9 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);