ext4: avoid allocating blocks from corrupted group in ext4_mb_try_best_found()

In the Linux kernel, the following vulnerability has been resolved: ext4: avoid allocating blocks from corrupted group in ext4_mb_try_best_found() Determine if the group block bitmap is corrupted before using ac_b_ex in ext4_mb_try_best_found() to avoid allocating blocks from a group with a corrupted block bitmap in the following concurrency and making the situation worse. ext4_mb_regular_allocator ext4_lock_group(sb, group) ext4_mb_good_group // check if the group bbitmap is corrupted ext4_mb_complex_scan_group // Scan group gets ac_b_ex but doesn't use it ext4_unlock_group(sb, group) ext4_mark_group_bitmap_corrupted(group) // The block bitmap was corrupted during // the group unlock gap. ext4_mb_try_best_found ext4_lock_group(ac->ac_sb, group) ext4_mb_use_best_found mb_mark_used // Allocating blocks in block bitmap corrupted group