[PATCH 5.11 013/601] tty: moxa: fix TIOCSSERIAL permission check

Greg Kroah-Hartman
2021-05-12T16:45:20Z

From: Johan Hovold <johan@kernel.org>

commit dc8c8437658667be9b11ec25c4b5482ed2becdaa upstream.

Changing the port close delay or type are privileged operations so make
sure to return -EPERM if a regular user tries to change them.

Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210407102334.32361-12-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/tty/moxa.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)

--- a/drivers/tty/moxa.c
+++ b/drivers/tty/moxa.c
@@ -2050,6 +2050,7 @@ static int moxa_set_serial_info(struct t
struct serial_struct *ss)
{
struct moxa_port *info = tty->driver_data;
+ unsigned int close_delay;

if (tty->index == MAX_PORTS)
return -EINVAL;
@@ -2061,19 +2062,24 @@ static int moxa_set_serial_info(struct t
ss->baud_base != 921600)
return -EPERM;

+ close_delay = msecs_to_jiffies(ss->close_delay * 10);
+
mutex_lock(&info->port.mutex);
if (!capable(CAP_SYS_ADMIN)) {
- if (((ss->flags & ~ASYNC_USR_MASK) !=
+ if (close_delay != info->port.close_delay ||
+ ss->type != info->type ||
+ ((ss->flags & ~ASYNC_USR_MASK) !=
(info->port.flags & ~ASYNC_USR_MASK))) {
mutex_unlock(&info->port.mutex);
return -EPERM;
}
- }
- info->port.close_delay = msecs_to_jiffies(ss->close_delay * 10);
+ } else {
+ info->port.close_delay = close_delay;

- MoxaSetFifo(info, ss->type == PORT_16550A);
+ MoxaSetFifo(info, ss->type == PORT_16550A);

- info->type = ss->type;
+ info->type = ss->type;
+ }
mutex_unlock(&info->port.mutex);
return 0;
}