[PATCH 5.15.y, 5.10.y] exfat: fix potential deadlock on __exfat_get_dentry_set

[Sherry Yang <sherry.yang@oracle.com>]

From: Sungjong Seo <sj1557.seo@samsung.com>

commit 89fc548767a2155231128cb98726d6d2ea1256c9 upstream.

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.

Fixes: a3ff29a95fde ("exfat: support dynamic allocate bh for exfat_entry_set_cache")
Cc: stable@vger.kernel.org # v6.2+
Reported-by: syzbot+412a392a2cd4a65e71db@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/lkml/000000000000fef47e0618c0327f@google.com
Signed-off-by: Sungjong Seo <sj1557.seo@samsung.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[Sherry: The problematic commit was backported to 5.15.y and 5.10.y,
thus backport this fix]
Signed-off-by: Sherry Yang <sherry.yang@oracle.com>
---
 fs/exfat/dir.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
index be7570d01ae1..0a1b1de032ef 100644
--- a/fs/exfat/dir.c
+++ b/fs/exfat/dir.c
@@ -878,7 +878,7 @@ struct exfat_entry_set_cache *exfat_get_dentry_set(struct super_block *sb,
 
 	num_bh = EXFAT_B_TO_BLK_ROUND_UP(off + num_entries * DENTRY_SIZE, sb);
 	if (num_bh > ARRAY_SIZE(es->__bh)) {
-		es->bh = kmalloc_array(num_bh, sizeof(*es->bh), GFP_KERNEL);
+		es->bh = kmalloc_array(num_bh, sizeof(*es->bh), GFP_NOFS);
 		if (!es->bh) {
 			brelse(bh);
 			kfree(es);
-- 
2.46.0