exfat: fix soft lockup in exfat_clear_bitmap

bitmap clear loop will take long time in __exfat_free_cluster()
if data size of file/dir enty is invalid.
If cluster bit in bitmap is already clear, stop clearing bitmap go to
out of loop.

Fixes: 3102386 ("exfat: add fat entry operations")
Reported-by: Kun Hu <huk23@m.fudan.edu.cn>, Jiaji Qin <jjtan24@m.fudan.edu.cn>
Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

Author: namjaejeon

fs/exfat/balloc.c

@@ -141,7 +141,7 @@ int exfat_set_bitmap(struct inode *inode, unsigned int clu, bool sync)
 	return 0;
 }
 
-void exfat_clear_bitmap(struct inode *inode, unsigned int clu, bool sync)
+int exfat_clear_bitmap(struct inode *inode, unsigned int clu, bool sync)
 {
 	int i, b;
 	unsigned int ent_idx;
@@ -150,13 +150,17 @@ void exfat_clear_bitmap(struct inode *inode, unsigned int clu, bool sync)
 	struct exfat_mount_options *opts = &sbi->options;
 
 	if (!is_valid_cluster(sbi, clu))
-		return;
+		return -EIO;
 
 	ent_idx = CLUSTER_TO_BITMAP_ENT(clu);
 	i = BITMAP_OFFSET_SECTOR_INDEX(sb, ent_idx);
 	b = BITMAP_OFFSET_BIT_IN_SECTOR(sb, ent_idx);
 
+	if (!test_bit_le(b, sbi->vol_amap[i]->b_data))
+		return -EIO;
+
 	clear_bit_le(b, sbi->vol_amap[i]->b_data);
+
 	exfat_update_bh(sbi->vol_amap[i], sync);
 
 	if (opts->discard) {
@@ -171,6 +175,8 @@ void exfat_clear_bitmap(struct inode *inode, unsigned int clu, bool sync)
 			opts->discard = 0;
 		}
 	}
+
+	return 0;
 }
 
 /*

fs/exfat/exfat_fs.h

@@ -456,7 +456,7 @@ int exfat_count_num_clusters(struct super_block *sb,
 int exfat_load_bitmap(struct super_block *sb);
 void exfat_free_bitmap(struct exfat_sb_info *sbi);
 int exfat_set_bitmap(struct inode *inode, unsigned int clu, bool sync);
-void exfat_clear_bitmap(struct inode *inode, unsigned int clu, bool sync);
+int exfat_clear_bitmap(struct inode *inode, unsigned int clu, bool sync);
 unsigned int exfat_find_free_bitmap(struct super_block *sb, unsigned int clu);
 int exfat_count_used_clusters(struct super_block *sb, unsigned int *ret_count);
 int exfat_trim_fs(struct inode *inode, struct fstrim_range *range);

fs/exfat/fatent.c

@@ -175,6 +175,7 @@ static int __exfat_free_cluster(struct inode *inode, struct exfat_chain *p_chain
 		BITMAP_OFFSET_SECTOR_INDEX(sb, CLUSTER_TO_BITMAP_ENT(clu));
 
 	if (p_chain->flags == ALLOC_NO_FAT_CHAIN) {
+		int err;
 		unsigned int last_cluster = p_chain->dir + p_chain->size - 1;
 		do {
 			bool sync = false;
@@ -189,7 +190,9 @@ static int __exfat_free_cluster(struct inode *inode, struct exfat_chain *p_chain
 				cur_cmap_i = next_cmap_i;
 			}
 
-			exfat_clear_bitmap(inode, clu, (sync && IS_DIRSYNC(inode)));
+			err = exfat_clear_bitmap(inode, clu, (sync && IS_DIRSYNC(inode)));
+			if (err)
+				break;
 			clu++;
 			num_clusters++;
 		} while (num_clusters < p_chain->size);
@@ -210,12 +213,13 @@ static int __exfat_free_cluster(struct inode *inode, struct exfat_chain *p_chain
 				cur_cmap_i = next_cmap_i;
 			}
 
-			exfat_clear_bitmap(inode, clu, (sync && IS_DIRSYNC(inode)));
+			if (exfat_clear_bitmap(inode, clu, (sync && IS_DIRSYNC(inode))))
+				break;
 			clu = n_clu;
 			num_clusters++;
 
 			if (err)
-				goto dec_used_clus;
+				break;
 
 			if (num_clusters >= sbi->num_clusters - EXFAT_FIRST_CLUSTER) {
 				/*
@@ -229,7 +233,6 @@ static int __exfat_free_cluster(struct inode *inode, struct exfat_chain *p_chain
 		} while (clu != EXFAT_EOF_CLUSTER);
 	}
 
-dec_used_clus:
 	sbi->used_clusters -= num_clusters;
 	return 0;
 }