Fixed a possible UAF problem in driver_override_show() in drivers/bus/fsl-mc/fsl-mc-bus.c

This function driver_override_show() is part of DEVICE_ATTR_RW, which includes both driver_override_show() and driver_override_store(). These functions can be executed concurrently in sysfs.

The driver_override_store() function uses driver_set_override() to update the driver_override value, and driver_set_override() internally locks the device (device_lock(dev)). If driver_override_show() reads cdx_dev->driver_override without locking, it could potentially access a freed pointer if driver_override_store() frees the string concurrently. This could lead to printing a kernel address, which is a security risk since DEVICE_ATTR can be read by all users.

Additionally, a similar pattern is used in drivers/amba/bus.c, as well as many other bus drivers, where device_lock() is taken in the show function, and it has been working without issues.

This potential bug was detected by our experimental static analysis tool, which analyzes locking APIs and paired functions to identify data races and atomicity violations.

Fixes: 1f86a00c1159 ("bus/fsl-mc: add support for 'driver_override' in the mc-bus") Cc: stable@vger.kernel.org Signed-off-by: Qiu-ji Chen chenqiuji666@gmail.com --- V2: Revised the description to reduce the confusion it caused. --- drivers/bus/fsl-mc/fsl-mc-bus.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/bus/fsl-mc/fsl-mc-bus.c b/drivers/bus/fsl-mc/fsl-mc-bus.c index 930d8a3ba722..62a9da88b4c9 100644 --- a/drivers/bus/fsl-mc/fsl-mc-bus.c +++ b/drivers/bus/fsl-mc/fsl-mc-bus.c @@ -201,8 +201,12 @@ static ssize_t driver_override_show(struct device *dev, struct device_attribute *attr, char *buf) { struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev); + ssize_t len;

- return snprintf(buf, PAGE_SIZE, "%s\n", mc_dev->driver_override); + device_lock(dev); + len = snprintf(buf, PAGE_SIZE, "%s\n", mc_dev->driver_override); + device_unlock(dev); + return len; } static DEVICE_ATTR_RW(driver_override);