Re: [PATCH] serial: core: fix TIOCSSERIAL and TIOCSERCONFIG on uninitialised ports

[Johan Hovold <johan@kernel.org>]

On Fri, Oct 09, 2026 at 11:46:16PM -0400, Hengyu Liang wrote:
> Commit 8ca59f7baee7 ("serial: fix ioctl hangup race") made
> uart_set_info() and uart_do_autoconfig() return -EIO when TTY_IO_ERROR
> is set, so that they do not run on a port that has been hung up.
> 
> However, TTY_IO_ERROR is also set on a port that could not be started,
> for example because its type is unknown, and by uart_shutdown(), which
> both functions call. As of now, setserial cannot configure a port that
> the kernel did not detect, and an autoconfig that follows a port, irq or
> type change in the same setserial call fails on any port.

Thanks for catching this.

How did you find it by the way? I assume you are not using an ISA serial
card?

> This patch will check tty_port_active() in these two functions instead.
> uart_hangup() clears it under the port mutex, and it stays set on an
> open port that could not be started.

Yeah, this should work. (And the flag is now also cleared under the port
mutex by tty_port_hangup(), which serial core currently does not use.)
 
> Fixes: 8ca59f7baee7 ("serial: fix ioctl hangup race")
> Cc: stable@vger.kernel.org
> Signed-off-by: Hengyu Liang <hengyul@cs.unc.edu>
> ---
> Commit 8ca59f7baee7 is in the stable queue for 7.2.
> 
> Tested on v7.3-rc6 in QEMU (8250). A TIOCSSERIAL that is held in
> copy_from_user() with userfaultfd while the tty is hung up with
> TIOCVHANGUP still gets -EIO from uart_set_info() with this patch.

Tested-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Johan Hovold <johan@kernel.org>

Johan