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>

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;
+			}
+
 		}
 	}
 

fs/exfat/fatent.c

@@ -490,5 +490,15 @@ int exfat_count_num_clusters(struct super_block *sb,
 	}
 
 	*ret_count = count;
+
+	/*
+	 * since exfat_count_used_clusters() is not called, sbi->used_clusters
+	 * cannot be used here.
+	 */
+	if (unlikely(i == sbi->num_clusters && clu != EXFAT_EOF_CLUSTER)) {
+		exfat_fs_error(sb, "The cluster chain has a loop");
+		return -EIO;
+	}
+
 	return 0;
 }

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;
 		}
 	}
 

fs/exfat/super.c

@@ -341,13 +341,12 @@ static void exfat_hash_init(struct super_block *sb)
 		INIT_HLIST_HEAD(&sbi->inode_hashtable[i]);
 }
 
-static int exfat_read_root(struct inode *inode)
+static int exfat_read_root(struct inode *inode, struct exfat_chain *root_clu)
 {
 	struct super_block *sb = inode->i_sb;
 	struct exfat_sb_info *sbi = EXFAT_SB(sb);
 	struct exfat_inode_info *ei = EXFAT_I(inode);
-	struct exfat_chain cdir;
+	int num_subdirs;
-	int num_subdirs, num_clu = 0;
 
 	exfat_chain_set(&ei->dir, sbi->root_dir, 0, ALLOC_FAT_CHAIN);
 	ei->entry = -1;
@@ -360,12 +359,9 @@ static int exfat_read_root(struct inode *inode)
 	ei->hint_stat.clu = sbi->root_dir;
 	ei->hint_femp.eidx = EXFAT_HINT_NONE;
 
-	exfat_chain_set(&cdir, sbi->root_dir, 0, ALLOC_FAT_CHAIN);
+	i_size_write(inode, EXFAT_CLU_TO_B(root_clu->size, sbi));
-	if (exfat_count_num_clusters(sb, &cdir, &num_clu))
-		return -EIO;
-	i_size_write(inode, num_clu << sbi->cluster_size_bits);
 
-	num_subdirs = exfat_count_dir_entries(sb, &cdir);
+	num_subdirs = exfat_count_dir_entries(sb, root_clu);
 	if (num_subdirs < 0)
 		return -EIO;
 	set_nlink(inode, num_subdirs + EXFAT_MIN_SUBDIR);
@@ -578,7 +574,8 @@ static int exfat_verify_boot_region(struct super_block *sb)
 }
 
 /* mount the file system volume */
-static int __exfat_fill_super(struct super_block *sb)
+static int __exfat_fill_super(struct super_block *sb,
+		struct exfat_chain *root_clu)
 {
 	int ret;
 	struct exfat_sb_info *sbi = EXFAT_SB(sb);
@@ -595,6 +592,18 @@ static int __exfat_fill_super(struct super_block *sb)
 		goto free_bh;
 	}
 
+	/*
+	 * Call exfat_count_num_cluster() before searching for up-case and
+	 * bitmap directory entries to avoid infinite loop if they are missing
+	 * and the cluster chain includes a loop.
+	 */
+	exfat_chain_set(root_clu, sbi->root_dir, 0, ALLOC_FAT_CHAIN);
+	ret = exfat_count_num_clusters(sb, root_clu, &root_clu->size);
+	if (ret) {
+		exfat_err(sb, "failed to count the number of clusters in root");
+		goto free_bh;
+	}
+
 	ret = exfat_create_upcase_table(sb);
 	if (ret) {
 		exfat_err(sb, "failed to load upcase table");
@@ -627,6 +636,7 @@ static int exfat_fill_super(struct super_block *sb, struct fs_context *fc)
 	struct exfat_sb_info *sbi = sb->s_fs_info;
 	struct exfat_mount_options *opts = &sbi->options;
 	struct inode *root_inode;
+	struct exfat_chain root_clu;
 	int err;
 
 	if (opts->allow_utime == (unsigned short)-1)
@@ -645,7 +655,7 @@ static int exfat_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_time_min = EXFAT_MIN_TIMESTAMP_SECS;
 	sb->s_time_max = EXFAT_MAX_TIMESTAMP_SECS;
 
-	err = __exfat_fill_super(sb);
+	err = __exfat_fill_super(sb, &root_clu);
 	if (err) {
 		exfat_err(sb, "failed to recognize exfat type");
 		goto check_nls_io;
@@ -680,7 +690,7 @@ static int exfat_fill_super(struct super_block *sb, struct fs_context *fc)
 
 	root_inode->i_ino = EXFAT_ROOT_INO;
 	inode_set_iversion(root_inode, 1);
-	err = exfat_read_root(root_inode);
+	err = exfat_read_root(root_inode, &root_clu);
 	if (err) {
 		exfat_err(sb, "failed to initialize root inode");
 		goto put_inode;