VT ioctl race fix

When calling the RELDISP VT ioctl, we are reading vt_newvt while the
console workqueue could be messing with it (through change_console()).  We
fix this race by taking the console semaphore before reading vt_newvt.

Signed-off-by: Samuel Ortiz <sameo@openedhand.com>
Acked-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/drivers/char/vt_ioctl.c b/drivers/char/vt_ioctl.c
index 045e6888d15b..c799b7f7bbb3 100644
--- a/drivers/char/vt_ioctl.c
+++ b/drivers/char/vt_ioctl.c
@@ -770,6 +770,7 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
                 /*
                  * Switching-from response
                  */
+                acquire_console_sem();
                 if (vc->vt_newvt >= 0) {
                         if (arg == 0)
                                 /*
@@ -784,7 +785,6 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
                                  * complete the switch.
                                  */
                                 int newvt;
-                                acquire_console_sem();
                                 newvt = vc->vt_newvt;
                                 vc->vt_newvt = -1;
                                 i = vc_allocate(newvt);
@@ -798,7 +798,6 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
                                  * other console switches..
                                  */
                                 complete_change_console(vc_cons[newvt].d);
-                                release_console_sem();
                         }
                 }
 
@@ -810,9 +809,12 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
                         /*
                          * If it's just an ACK, ignore it
                          */
-                        if (arg != VT_ACKACQ)
+                        if (arg != VT_ACKACQ) {
+                                release_console_sem();
                                 return -EINVAL;
+                        }
                 }
+                release_console_sem();
 
                 return 0;