exfat: add cluster chain loop check for dir

An infinite loop may occur if the following conditions occur due to
file system corruption.

(1) Condition for exfat_count_dir_entries() to loop infinitely.
    - The cluster chain includes a loop.
    - There is no UNUSED entry in the cluster chain.

(2) Condition for exfat_create_upcase_table() to loop infinitely.
    - The cluster chain of the root directory includes a loop.
    - There are no UNUSED entry and up-case table entry in the cluster
      chain of the root directory.

(3) Condition for exfat_load_bitmap() to loop infinitely.
    - The cluster chain of the root directory includes a loop.
    - There are no UNUSED entry and bitmap entry in the cluster chain
      of the root directory.

(4) Condition for exfat_find_dir_entry() to loop infinitely.
    - The cluster chain includes a loop.
    - The unused directory entries were exhausted by some operation.

(5) Condition for exfat_check_dir_empty() to loop infinitely.
    - The cluster chain includes a loop.
    - The unused directory entries were exhausted by some operation.
    - All files and sub-directories under the directory are deleted.

This commit adds checks to break the above infinite loop.

Signed-off-by: Yuezhang Mo <Yuezhang.Mo@sony.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/exfat/namei.c b/fs/exfat/namei.c
index fede0283d6e2..f5f1c4e8a29f 100644
--- a/fs/exfat/namei.c
+++ b/fs/exfat/namei.c
@@ -890,6 +890,7 @@ static int exfat_check_dir_empty(struct super_block *sb,
 {
 	int i, dentries_per_clu;
 	unsigned int type;
+	unsigned int clu_count = 0;
 	struct exfat_chain clu;
 	struct exfat_dentry *ep;
 	struct exfat_sb_info *sbi = EXFAT_SB(sb);
@@ -926,6 +927,10 @@ static int exfat_check_dir_empty(struct super_block *sb,
 		} else {
 			if (exfat_get_next_cluster(sb, &(clu.dir)))
 				return -EIO;
+
+			/* break if the cluster chain includes a loop */
+			if (unlikely(++clu_count > EXFAT_DATA_CLUSTER_COUNT(sbi)))
+				break;
 		}
 	}