CVE-2024-57940: Loop with Unreachable Exit Condition

In the Linux kernel, the following vulnerability has been resolved:

exfat: fix the infinite loop in exfat_readdir()

If the file system is corrupted so that a cluster is linked to itself in the cluster chain, and there is an unused directory entry in the cluster, 'dentry' will not be incremented, causing condition 'dentry < max_dentries' unable to prevent an infinite loop.

This infinite loop causes s_lock not to be released, and other tasks will hang, such as exfat_sync_fs().

This commit stops traversing the cluster chain when there is unused directory entry in the cluster to avoid this infinite loop.