tty: fix data race in flush_to_ldisc
authorDmitry Vyukov <dvyukov@google.com>
Thu, 17 Sep 2015 15:17:08 +0000 (17:17 +0200)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Sun, 4 Oct 2015 18:03:40 +0000 (19:03 +0100)
flush_to_ldisc reads port->itty and checks that it is not NULL,
concurrently release_tty sets port->itty to NULL. It is possible
that flush_to_ldisc loads port->itty once, ensures that it is
not NULL, but then reloads it again and uses. The second load
can already return NULL, which will cause a crash.

Use READ_ONCE to read port->itty.

The data race was found with KernelThreadSanitizer (KTSAN).

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
drivers/tty/tty_buffer.c

index 5a3fa89138801ea63907ec102fbb589b36d7201c..23de97de09a4d9ca0c9885b2a34949a713ec7f3b 100644 (file)
@@ -467,7 +467,7 @@ static void flush_to_ldisc(struct work_struct *work)
        struct tty_struct *tty;
        struct tty_ldisc *disc;
 
-       tty = port->itty;
+       tty = READ_ONCE(port->itty);
        if (tty == NULL)
                return;