[PATCH] drivers/serial/serial_core.c: prevent reading uninitialized stack memory

[Dan Rosenberg <drosenberg@vsecurity.com>]

The TIOCGICOUNT device ioctl allows unprivileged users to read
uninitialized stack memory, because the "reserved" member of the
serial_icounter_struct struct declared on the stack is not altered or
zeroed before being copied back to the user.  This patch takes care of
it.

Signed-off-by: Dan Rosenberg <dan.j.rosenberg@gmail.com>

--- linux-2.6.35.4.orig/drivers/serial/serial_core.c	2010-08-26 19:47:12.000000000 -0400
+++ linux-2.6.35.4/drivers/serial/serial_core.c	2010-09-15 13:57:04.767375072 -0400
@@ -1081,6 +1081,8 @@ static int uart_get_count(struct uart_st
 	struct uart_icount cnow;
 	struct uart_port *uport = state->uart_port;
 
+	memset(&icount, 0, sizeof(struct serial_icounter_struct));
+
 	spin_lock_irq(&uport->lock);
 	memcpy(&cnow, &uport->icount, sizeof(struct uart_icount));
 	spin_unlock_irq(&uport->lock);