CVE-2024-26773: 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 ext4mbtrybestfound()

Determine if the group block bitmap is corrupted before using acbex in ext4mbtrybestfound() to avoid allocating blocks from a group with a corrupted block bitmap in the following concurrency and making the situation worse.

ext4mbregularallocator ext4lockgroup(sb, group) ext4mbgoodgroup // check if the group bbitmap is corrupted ext4mbcomplexscangroup // Scan group gets acbex but doesn't use it ext4unlockgroup(sb, group) ext4markgroupbitmapcorrupted(group) // The block bitmap was corrupted during // the group unlock gap. ext4mbtrybestfound ext4lockgroup(ac->acsb, group) ext4mbusebestfound mbmarkused // Allocating blocks in block bitmap corrupted group