exfat: fix the infinite loop in exfat_readdir()

Vulnerability Description

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.

References

• https://git.kernel.org/stable/c/d8cfbb8723bd3d3222f360227a1cc15227189ca6
• https://git.kernel.org/stable/c/28c21f0ac5293a4bf19b3e0e32005d6dd31a6c17
• https://git.kernel.org/stable/c/31beabd0f47f8c3ed9965ba861c9e5b252d4920a
• https://git.kernel.org/stable/c/dc1d7afceb982e8f666e70a582e6b5aa806de063
• https://git.kernel.org/stable/c/d9ea94f5cd117d56e573696d0045ab3044185a15
• https://git.kernel.org/stable/c/fee873761bd978d077d8c55334b4966ac4cb7b59