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X-CSE-ConnectionGUID: 3HqxtwvuQraKPcVgGOYwng== X-CSE-MsgGUID: c9/dzUdDQW2yCNDTBCdt7w== X-IronPort-AV: E=McAfee;i="6700,10204,11450"; a="54663190" X-IronPort-AV: E=Sophos;i="6.16,203,1744095600"; d="scan'208";a="54663190" Received: from orviesa002.jf.intel.com ([10.64.159.142]) by fmvoesa106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Jun 2025 03:31:54 -0700 X-CSE-ConnectionGUID: upffi4pmToyCms5RGbbhLg== X-CSE-MsgGUID: 70AqVy+mQyaUZfPdmCMFEQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.16,203,1744095600"; d="scan'208";a="175482926" Received: from ijarvine-mobl1.ger.corp.intel.com (HELO localhost) ([10.245.245.134]) by orviesa002-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Jun 2025 03:31:53 -0700 From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= Date: Mon, 2 Jun 2025 13:31:49 +0300 (EEST) To: Max Staudt cc: Greg Kroah-Hartman , Jiri Slaby , Johan Hovold , linux-serial , LKML , stable@vger.kernel.org Subject: Re: [PATCH v2 2/2] tty: Fix race against tty_open() in tty_register_device_attr() In-Reply-To: <20250528132816.11433-2-max@enpas.org> Message-ID: <6068387e-7064-0c2b-700a-3817bea1045b@linux.intel.com> References: <20250528132816.11433-1-max@enpas.org> <20250528132816.11433-2-max@enpas.org> Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII On Wed, 28 May 2025, Max Staudt wrote: > Since the chardev is now created before the class device is registered, > an attempt to tty_[k]open() the chardev between these two steps will > lead to tty->dev being assigned NULL by alloc_tty_struct(). > > alloc_tty_struct() is called via tty_init_dev() when the tty is firstly > opened, and is entered with tty_mutex held, so let's lock the critical > section in tty_register_device_attr() with the same global mutex. > This guarantees that tty->dev can be assigned a sane value. > > Fixes: 6a7e6f78c235 ("tty: close race between device register and open") > Signed-off-by: Max Staudt > Cc: > --- > drivers/tty/tty_io.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c > index e922b84524d2..94768509e2d2 100644 > --- a/drivers/tty/tty_io.c > +++ b/drivers/tty/tty_io.c > @@ -3258,6 +3258,8 @@ struct device *tty_register_device_attr(struct tty_driver *driver, > else > tty_line_name(driver, index, name); > > + mutex_lock(&tty_mutex); Use guard() so you don't need to change the returns and rollback path. > + > if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC)) { > /* > * Free any saved termios data so that the termios state is > @@ -3271,7 +3273,7 @@ struct device *tty_register_device_attr(struct tty_driver *driver, > > retval = tty_cdev_add(driver, devt, index, 1); > if (retval) > - return ERR_PTR(retval); > + goto err_unlock; > > cdev_added = true; > } > @@ -3294,6 +3296,8 @@ struct device *tty_register_device_attr(struct tty_driver *driver, > if (retval) > goto err_put; > > + mutex_unlock(&tty_mutex); > + > return dev; > > err_put: > @@ -3309,6 +3313,9 @@ struct device *tty_register_device_attr(struct tty_driver *driver, > driver->cdevs[index] = NULL; > } > > +err_unlock: > + mutex_unlock(&tty_mutex); > + > return ERR_PTR(retval); > } > EXPORT_SYMBOL_GPL(tty_register_device_attr); > -- i.