The driver_override_show() function reads the driver_override string without holding the device_lock. However, driver_override_store() uses driver_set_override(), which modifies and frees the string while holding the device_lock.
This can result in a concurrent use-after-free if the string is freed by the store function while being read by the show function.
Fix this by holding the device_lock around the read operation.
Fixes: 1f86a00c1159 ("bus/fsl-mc: add support for 'driver_override' in the mc-bus") Cc: stable@vger.kernel.org Signed-off-by: Gui-Dong Han hanguidong02@gmail.com --- I verified this with a stress test that continuously writes/reads the attribute. It triggered KASAN and leaked bytes like a0 f4 81 9f a3 ff ff (likely kernel pointers). Since driver_override is world-readable (0644), this allows unprivileged users to leak kernel pointers and bypass KASLR. Similar races were fixed in other buses (e.g., commits 9561475db680 and 91d44c1afc61). Currently, 9 of 11 buses handle this correctly; this patch fixes one of the remaining two. --- 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 25845c04e562..a97baf2cbcdd 100644 --- a/drivers/bus/fsl-mc/fsl-mc-bus.c +++ b/drivers/bus/fsl-mc/fsl-mc-bus.c @@ -202,8 +202,12 @@ 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 sysfs_emit(buf, "%s\n", mc_dev->driver_override); + device_lock(dev); + len = sysfs_emit(buf, "%s\n", mc_dev->driver_override); + device_unlock(dev); + return len; } static DEVICE_ATTR_RW(driver_override);