5.4-stable review patch. If anyone has any objections, please let me know.
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From: Oliver Neukum oneukum@suse.com
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 --- drivers/usb/class/cdc-acm.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/drivers/usb/class/cdc-acm.c +++ b/drivers/usb/class/cdc-acm.c @@ -938,10 +938,12 @@ static int get_serial_info(struct tty_st 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; }