Commit ac4d8bb6 authored by Danilo Krummrich's avatar Danilo Krummrich
Browse files

s390/cio: use generic driver_override infrastructure 

When a driver is probed through __driver_attach(), the bus' match()
callback is called without the device lock held, thus accessing the
driver_override field without a lock, which can cause a UAF.

Fix this by using the driver-core driver_override infrastructure taking
care of proper locking internally.

Note that calling match() from __driver_attach() without the device lock
held is intentional. [1]

Link: https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@kernel.org/

 [1]
Reported-by: default avatarGui-Dong Han <hanguidong02@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220789


Fixes: ebc3d179 ("s390/cio: introduce driver_override on the css bus")
Reviewed-by: default avatarVineeth Vijayan <vneethv@linux.ibm.com>
Link: https://patch.msgid.link/20260324005919.2408620-10-dakr@kernel.org


Signed-off-by: default avatarDanilo Krummrich <dakr@kernel.org>
parent 85bb534f

drivers/s390/cio/cio.h

+0 −5
Original line number Diff line number Diff line
@@ -103,11 +103,6 @@ struct subchannel { 
	struct work_struct todo_work;

	struct schib_config config;

	u64 dma_mask;

	/*

	 * Driver name to force a match.  Do not set directly, because core

	 * frees it.  Use driver_set_override() to set or clear it.

	 */

	const char *driver_override;

} __attribute__ ((aligned(8)));



DECLARE_PER_CPU_ALIGNED(struct irb, cio_irb);

drivers/s390/cio/css.c

+4 −30
Original line number Diff line number Diff line
@@ -159,7 +159,6 @@ static void css_subchannel_release(struct device *dev) 


	sch->config.intparm = 0;

	cio_commit_config(sch);

	kfree(sch->driver_override);

	kfree(sch);

}
@@ -323,37 +322,9 @@ static ssize_t modalias_show(struct device *dev, struct device_attribute *attr, 


static DEVICE_ATTR_RO(modalias);



static ssize_t driver_override_store(struct device *dev,

				     struct device_attribute *attr,

				     const char *buf, size_t count)

{

	struct subchannel *sch = to_subchannel(dev);

	int ret;



	ret = driver_set_override(dev, &sch->driver_override, buf, count);

	if (ret)

		return ret;



	return count;

}



static ssize_t driver_override_show(struct device *dev,

				    struct device_attribute *attr, char *buf)

{

	struct subchannel *sch = to_subchannel(dev);

	ssize_t len;



	device_lock(dev);

	len = sysfs_emit(buf, "%s\n", sch->driver_override);

	device_unlock(dev);

	return len;

}

static DEVICE_ATTR_RW(driver_override);



static struct attribute *subch_attrs[] = {

	&dev_attr_type.attr,

	&dev_attr_modalias.attr,

	&dev_attr_driver_override.attr,

	NULL,

};
@@ -1356,9 +1327,11 @@ static int css_bus_match(struct device *dev, const struct device_driver *drv) 
	struct subchannel *sch = to_subchannel(dev);

	const struct css_driver *driver = to_cssdriver(drv);

	struct css_device_id *id;

	int ret;



	/* When driver_override is set, only bind to the matching driver */

	if (sch->driver_override && strcmp(sch->driver_override, drv->name))

	ret = device_match_driver_override(dev, drv);

	if (ret == 0)

		return 0;



	for (id = driver->subchannel_type; id->match_flags; id++) {
@@ -1415,6 +1388,7 @@ static int css_uevent(const struct device *dev, struct kobj_uevent_env *env) 


static const struct bus_type css_bus_type = {

	.name     = "css",

	.driver_override = true,

	.match    = css_bus_match,

	.probe    = css_probe,

	.remove   = css_remove,