CVE-2024-42315 exfat: fix potential deadlock on __exfat_get_dentry_set

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

exfat: fix potential deadlock on __exfat_get_dentry_set

When accessing a file with more entries than ES_MAX_ENTRY_NUM, the bh-array
is allocated in __exfat_get_entry_set. The problem is that the bh-array is
allocated with GFP_KERNEL. It does not make sense. In the following cases,
a deadlock for sbi->s_lock between the two processes may occur.

   CPU0                CPU1
   ----                ----

kswapd
balance_pgdat
lock(fs_reclaim)
exfat_iterate
lock(&sbi->s_lock)
exfat_readdir
exfat_get_uniname_from_ext_entry
exfat_get_dentry_set
__exfat_get_dentry_set
kmalloc_array
…
lock(fs_reclaim)
…
evict
exfat_evict_inode
lock(&sbi->s_lock)

To fix this, let’s allocate bh-array with GFP_NOFS.