-stable review patch. If anyone has any objections, please let us know.
------------------
From: Michal Januszewski <[email protected]>
[PATCH] vt: fix potential race in VT_WAITACTIVE handler
On a multiprocessor machine the VT_WAITACTIVE ioctl call may return 0 if
fg_console has already been updated in redraw_screen() but the console
switch itself hasn't been completed. Fix this by checking fg_console in
vt_waitactive() with the console sem held.
Signed-off-by: Michal Januszewski <[email protected]>
Acked-by: Antonino Daplas <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Cc: Chuck Ebbert <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
drivers/char/vt_ioctl.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
--- a/drivers/char/vt_ioctl.c
+++ b/drivers/char/vt_ioctl.c
@@ -1038,10 +1038,22 @@ int vt_waitactive(int vt)
add_wait_queue(&vt_activate_queue, &wait);
for (;;) {
- set_current_state(TASK_INTERRUPTIBLE);
retval = 0;
- if (vt == fg_console)
+
+ /*
+ * Synchronize with redraw_screen(). By acquiring the console
+ * semaphore we make sure that the console switch is completed
+ * before we return. If we didn't wait for the semaphore, we
+ * could return at a point where fg_console has already been
+ * updated, but the console switch hasn't been completed.
+ */
+ acquire_console_sem();
+ set_current_state(TASK_INTERRUPTIBLE);
+ if (vt == fg_console) {
+ release_console_sem();
break;
+ }
+ release_console_sem();
retval = -EINTR;
if (signal_pending(current))
break;
--
-
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