| Message ID | 20250430111617.1151390-1-quic_cxin@quicinc.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v1] tty: serdev: serdev-ttyport: Fix use-after-free in ttyport_close() due to uninitialized serport->tty | expand |
On 4/30/2025 7:40 PM, Greg Kroah-Hartman wrote: > On Wed, Apr 30, 2025 at 07:16:17PM +0800, Xin Chen wrote: >> When ttyport_open() fails to initialize a tty device, serport->tty is not >> --- a/drivers/tty/serdev/serdev-ttyport.c >> +++ b/drivers/tty/serdev/serdev-ttyport.c >> @@ -88,6 +88,10 @@ static void ttyport_write_flush(struct serdev_controller *ctrl) >> { >> struct serport *serport = serdev_controller_get_drvdata(ctrl); >> struct tty_struct *tty = serport->tty; >> + if (!tty) { >> + dev_err(&ctrl->dev, "tty is null\n"); >> + return; >> + } > > What prevents tty from going NULL right after you just checked this? First sorry for reply so late for I have a long statutory holidays. Maybe I don't get your point. From my side, there is nothing to prevent it. Check here is to avoid code go on if tty is NULL. > > And why print out that message, what can userspace do with it? > I add the print just ref to code in other place. This can't be used by userspace, but it can be used in DMesg log when system crashes. >> >> tty_driver_flush_buffer(tty); >> } >> @@ -108,8 +112,10 @@ static int ttyport_open(struct serdev_controller *ctrl) >> int ret; >> >> tty = tty_init_dev(serport->tty_drv, serport->tty_idx); >> - if (IS_ERR(tty)) >> + if (IS_ERR(tty)) { >> + serport->tty = NULL; >> return PTR_ERR(tty); >> + } >> serport->tty = tty; >> >> if (!tty->ops->open || !tty->ops->close) { >> @@ -156,6 +162,11 @@ static void ttyport_close(struct serdev_controller *ctrl) >> >> clear_bit(SERPORT_ACTIVE, &serport->flags); >> >> + if (!tty) { >> + dev_err(&ctrl->dev, "tty is null\n"); >> + return; >> + } > > Again, what prevents it from changing right after you just checked it? Same with above, there is nothing prevent it. Check here is to avoid code go on if tty is NULL. The check is for changes in ttyport_open(). In my project, it's possible that ttyport_close() and ttyport_write_flush() get called after ttyport_open() failed, at which time tty is invalid. thanks, Xin
On Thu, May 08, 2025 at 05:29:18PM +0800, Xin Chen wrote: > > On 4/30/2025 7:40 PM, Greg Kroah-Hartman wrote: > > On Wed, Apr 30, 2025 at 07:16:17PM +0800, Xin Chen wrote: > >> When ttyport_open() fails to initialize a tty device, serport->tty is not > >> --- a/drivers/tty/serdev/serdev-ttyport.c > >> +++ b/drivers/tty/serdev/serdev-ttyport.c > >> @@ -88,6 +88,10 @@ static void ttyport_write_flush(struct serdev_controller *ctrl) > >> { > >> struct serport *serport = serdev_controller_get_drvdata(ctrl); > >> struct tty_struct *tty = serport->tty; > >> + if (!tty) { > >> + dev_err(&ctrl->dev, "tty is null\n"); > >> + return; > >> + } > > > > What prevents tty from going NULL right after you just checked this? > > First sorry for reply so late for I have a long statutory holidays. > Maybe I don't get your point. From my side, there is nothing to prevent it. > Check here is to avoid code go on if tty is NULL. Yes, but the problem is, serport->tty could change to be NULL right after you check it, so you have not removed the real race that can happen here. There is no lock, so by adding this check you are only reducing the risk of the problem happening, not actually fixing the issue so that it will never happen. Please fix it so that this can never happen. thanks, greg k-h
diff --git a/drivers/tty/serdev/serdev-ttyport.c b/drivers/tty/serdev/serdev-ttyport.c index 3d7ae7fa5018..287908f2009b 100644 --- a/drivers/tty/serdev/serdev-ttyport.c +++ b/drivers/tty/serdev/serdev-ttyport.c @@ -88,6 +88,10 @@ static void ttyport_write_flush(struct serdev_controller *ctrl) { struct serport *serport = serdev_controller_get_drvdata(ctrl); struct tty_struct *tty = serport->tty; + if (!tty) { + dev_err(&ctrl->dev, "tty is null\n"); + return; + } tty_driver_flush_buffer(tty); } @@ -108,8 +112,10 @@ static int ttyport_open(struct serdev_controller *ctrl) int ret; tty = tty_init_dev(serport->tty_drv, serport->tty_idx); - if (IS_ERR(tty)) + if (IS_ERR(tty)) { + serport->tty = NULL; return PTR_ERR(tty); + } serport->tty = tty; if (!tty->ops->open || !tty->ops->close) { @@ -156,6 +162,11 @@ static void ttyport_close(struct serdev_controller *ctrl) clear_bit(SERPORT_ACTIVE, &serport->flags); + if (!tty) { + dev_err(&ctrl->dev, "tty is null\n"); + return; + } + tty_lock(tty); if (tty->ops->close) tty->ops->close(tty, NULL);