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, 12 insertions, 0 deletions

diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
index 3103b932b674..ee060e26f51d 100644
--- a/fs/exfat/dir.c
+++ b/fs/exfat/dir.c
@@ -996,6 +996,7 @@ int exfat_find_dir_entry(struct super_block *sb, struct exfat_inode_info *ei,
 	struct exfat_hint_femp candi_empty;
 	struct exfat_sb_info *sbi = EXFAT_SB(sb);
 	int num_entries = exfat_calc_num_entries(p_uniname);
+	unsigned int clu_count = 0;
 
 	if (num_entries < 0)
 		return num_entries;
@@ -1133,6 +1134,10 @@ rewind:
 		} 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)))
+				goto not_found;
 		}
 	}
 
@@ -1195,6 +1200,7 @@ int exfat_count_dir_entries(struct super_block *sb, struct exfat_chain *p_dir)
 	int i, count = 0;
 	int dentries_per_clu;
 	unsigned int entry_type;
+	unsigned int clu_count = 0;
 	struct exfat_chain clu;
 	struct exfat_dentry *ep;
 	struct exfat_sb_info *sbi = EXFAT_SB(sb);
@@ -1227,6 +1233,12 @@ int exfat_count_dir_entries(struct super_block *sb, struct exfat_chain *p_dir)
 		} else {
 			if (exfat_get_next_cluster(sb, &(clu.dir)))
 				return -EIO;
+
+			if (unlikely(++clu_count > sbi->used_clusters)) {
+				exfat_fs_error(sb, "FAT or bitmap is corrupted");
+				return -EIO;
+			}
+
 		}
 	}