[PATCH] vt: fix potential race in VT_WAITACTIVE handler (f991519c) · Commits · 戴 / test

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 <spock@gentoo.org> Acked-by:

Antonino Daplas <adaplas@pol.net> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/vt_ioctl.c

+14 −2

Original line number	Diff line number	Diff line
		@@ -1039,10 +1039,22 @@ 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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