The driver_override_show function reads the driver_override string without holding the device_lock. However, the store function modifies and frees the string while holding the device_lock. This creates a race condition where the string can be freed by the store function while being read by the show function, leading to a use-after-free.

To fix this, replace the rpmsg_string_attr macro with explicit show and store functions. The new driver_override_store uses the standard driver_set_override helper. Since the introduction of driver_set_override, the comments in include/linux/rpmsg.h have stated that this helper must be used to set or clear driver_override, but the implementation was not updated until now.

Because driver_set_override modifies and frees the string while holding the device_lock, the new driver_override_show now correctly holds the device_lock during the read operation to prevent the race.

Additionally, since rpmsg_string_attr has only ever been used for driver_override, removing the macro simplifies the code.

Fixes: 39e47767ec9b ("rpmsg: Add driver_override device attribute for rpmsg_device") 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/rpmsg/rpmsg_core.c | 66 ++++++++++++++++---------------------- 1 file changed, 27 insertions(+), 39 deletions(-)

diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c index 5d661681a9b6..96964745065b 100644 --- a/drivers/rpmsg/rpmsg_core.c +++ b/drivers/rpmsg/rpmsg_core.c @@ -352,50 +352,38 @@ field##_show(struct device *dev, \ } \ static DEVICE_ATTR_RO(field);

-#define rpmsg_string_attr(field, member) \ -static ssize_t \ -field##_store(struct device *dev, struct device_attribute *attr, \ - const char *buf, size_t sz) \ -{ \ - struct rpmsg_device *rpdev = to_rpmsg_device(dev); \ - const char *old; \ - char *new; \ - \ - new = kstrndup(buf, sz, GFP_KERNEL); \ - if (!new) \ - return -ENOMEM; \ - new[strcspn(new, "\n")] = '\0'; \ - \ - device_lock(dev); \ - old = rpdev->member; \ - if (strlen(new)) { \ - rpdev->member = new; \ - } else { \ - kfree(new); \ - rpdev->member = NULL; \ - } \ - device_unlock(dev); \ - \ - kfree(old); \ - \ - return sz; \ -} \ -static ssize_t \ -field##_show(struct device *dev, \ - struct device_attribute *attr, char *buf) \ -{ \ - struct rpmsg_device *rpdev = to_rpmsg_device(dev); \ - \ - return sprintf(buf, "%s\n", rpdev->member); \ -} \ -static DEVICE_ATTR_RW(field) - /* for more info, see Documentation/ABI/testing/sysfs-bus-rpmsg */ rpmsg_show_attr(name, id.name, "%s\n"); rpmsg_show_attr(src, src, "0x%x\n"); rpmsg_show_attr(dst, dst, "0x%x\n"); rpmsg_show_attr(announce, announce ? "true" : "false", "%s\n"); -rpmsg_string_attr(driver_override, driver_override); + +static ssize_t driver_override_store(struct device *dev, + struct device_attribute *attr, + const char *buf, size_t count) +{ + struct rpmsg_device *rpdev = to_rpmsg_device(dev); + int ret; + + ret = driver_set_override(dev, &rpdev->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 rpmsg_device *rpdev = to_rpmsg_device(dev); + ssize_t len; + + device_lock(dev); + len = sysfs_emit(buf, "%s\n", rpdev->driver_override); + device_unlock(dev); + return len; +} +static DEVICE_ATTR_RW(driver_override);

static ssize_t modalias_show(struct device *dev, struct device_attribute *attr, char *buf)