[PATCH] exfat: fix potential deadlock on __exfat_get_dentry_set

[Sungjong Seo]

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@xxxxxxxxxxxxxxx # v6.2+
Reported-by: syzbot+412a392a2cd4a65e71db@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/lkml/000000000000fef47e0618c0327f@xxxxxxxxxx
Signed-off-by: Sungjong Seo <sj1557.seo@xxxxxxxxxxx>
---
 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 84572e11cc05..7446bf09a04a 100644
--- a/fs/exfat/dir.c
+++ b/fs/exfat/dir.c
@@ -813,7 +813,7 @@ static int __exfat_get_dentry_set(struct exfat_entry_set_cache *es,
 
 	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);
 			return -ENOMEM;
-- 
2.25.1