[PATCH] vt: rework the console spawning variables

This is such a rare path it took me a while to figure out how to test
this after soring out the locking.

This patch does several things.
- The variables used are moved into a structure and declared in vt_kern.h
- A spinlock is added so we don't have SMP races updating the values.
- Instead of raw pid_t value a struct_pid is used to guard against
  pid wrap around issues, if the daemon to spawn a new console dies.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 6 insertions, 3 deletions

diff --git a/drivers/char/vt_ioctl.c b/drivers/char/vt_ioctl.c
index a53e382cc107..dc408af165ab 100644
--- a/drivers/char/vt_ioctl.c
+++ b/drivers/char/vt_ioctl.c
@@ -645,13 +645,16 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
          */
         case KDSIGACCEPT:
         {
-                extern int spawnpid, spawnsig;
                 if (!perm || !capable(CAP_KILL))
                   return -EPERM;
                 if (!valid_signal(arg) || arg < 1 || arg == SIGKILL)
                   return -EINVAL;
-                spawnpid = current->pid;
-                spawnsig = arg;
+
+                spin_lock_irq(&vt_spawn_con.lock);
+                put_pid(vt_spawn_con.pid);
+                vt_spawn_con.pid = get_pid(task_pid(current));
+                vt_spawn_con.sig = arg;
+                spin_unlock_irq(&vt_spawn_con.lock);
                 return 0;
         }