CVE-2024-26774 ext4: avoid dividing by 0 in mb_update_avg_fragment_size() when block bitmap corrupt

In the Linux kernel, the following vulnerability has been resolved: ext4: avoid dividing by 0 in mbupdateavgfragmentsize when block bitmap corrupt Determine if bbfragments is 0 instead of determining bbfree to eliminate the risk of dividing by zero when the block bitmap is corrupted...