USB: class: CDC-ACM: fix race between get_serial and set_serial

commit b41c1fa155ba56d125885b0191aabaf3c508d0a3 upstream.

TIOCGSERIAL is an ioctl. Thus it must be atomic. It returns
two values. Racing with set_serial it can return an inconsistent
result. The mutex must be taken.

In terms of logic the bug is as old as the driver. In terms of
code it goes back to the conversion to the get_serial and
set_serial methods.

Signed-off-by: Oliver Neukum <oneukum@suse.com>
Cc: stable <stable@kernel.org>
Fixes: 99f75a1fcd865 ("cdc-acm: switch to ->[sg]et_serial()")
Link: https://lore.kernel.org/r/20240912141916.1044393-1-oneukum@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 2957a17b185e77b7d62c49cdc1f0d739d7a350bf..4871d0f09f6bacf6d7f0be4d980c58e8c401bd71 100644 (file)
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -942,10 +942,12 @@ static int get_serial_info(struct tty_struct *tty, struct serial_struct *ss)
        struct acm *acm = tty->driver_data;
 
        ss->line = acm->minor;
+       mutex_lock(&acm->port.mutex);
        ss->close_delay = jiffies_to_msecs(acm->port.close_delay) / 10;
        ss->closing_wait = acm->port.closing_wait == ASYNC_CLOSING_WAIT_NONE ?
                                ASYNC_CLOSING_WAIT_NONE :
                                jiffies_to_msecs(acm->port.closing_wait) / 10;
+       mutex_unlock(&acm->port.mutex);
        return 0;
 }