md/raid5: fix possible null-pointer dereferences in raid5_store_group_thread_cnt()

The variable mddev->private is first assigned to conf and then checked:

  conf = mddev->private;
  if (!conf) ...

If conf is NULL, then mddev->private is also NULL. In this case,
null-pointer dereferences can occur when calling raid5_quiesce():

  raid5_quiesce(mddev, true);
  raid5_quiesce(mddev, false);

since mddev->private is assigned to conf again in raid5_quiesce(), and conf
is dereferenced in several places, for example:

  conf->quiesce = 0;
  wake_up(&conf->wait_for_quiescent);

To fix this issue, the function should unlock mddev and return before
invoking raid5_quiesce() when conf is NULL, following the existing pattern
in raid5_change_consistency_policy().

Fixes: fa1944bbe622 ("md/raid5: Wait sync io to finish before changing group cnt")
Signed-off-by: Tuo Li <islituo@gmail.com>
Reviewed-by: Xiao Ni <xni@redhat.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Link: https://lore.kernel.org/linux-raid/20251225130326.67780-1-islituo@gmail.com
Signed-off-by: Yu Kuai <yukuai@fnnas.com>

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index e57ce3295292ba0d5ebb74237a23512ea3efd89f..8dc98f545969ff28ec0120d185ecd84f09f37392 100644 (file)
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -7187,12 +7187,14 @@ raid5_store_group_thread_cnt(struct mddev *mddev, const char *page, size_t len)
        err = mddev_suspend_and_lock(mddev);
        if (err)
                return err;
+       conf = mddev->private;
+       if (!conf) {
+               mddev_unlock_and_resume(mddev);
+               return -ENODEV;
+       }
        raid5_quiesce(mddev, true);
 
-       conf = mddev->private;
-       if (!conf)
-               err = -ENODEV;
-       else if (new != conf->worker_cnt_per_group) {
+       if (new != conf->worker_cnt_per_group) {
                old_groups = conf->worker_groups;
                if (old_groups)
                        flush_workqueue(raid5_wq);