serial_core:recognize invalid pointer from userspace

[Jiang Lu]

compat_ioctl use 0xffffffff as a magic number to mark invalid pointer
for iomem_base in serial_struct when truncating a 64bit pointer into
32bit.

Serial driver need recognize this invalid pointer when parsing
serial_struct from userspace.

Signed-off-by: Jiang Lu <lu.jiang@xxxxxxxxxxxxx>
---
 drivers/tty/serial/serial_core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index a5d545e..7b9ec1b 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -745,6 +745,9 @@ static int uart_set_info(struct tty_struct *tty, struct tty_port *port,
 	 * allocations, we should treat type changes the same as
 	 * IO port changes.
 	 */
+	if ((unsigned long)new_info->iomem_base == 0xffffffff)
+		new_info->iomem_base = (unsigned char *)uport->mapbase;
+
 	change_port = !(uport->flags & UPF_FIXED_PORT)
 		&& (new_port != uport->iobase ||
 		    (unsigned long)new_info->iomem_base != uport->mapbase ||
-- 
1.9.1