ext4: avoid negative min_clusters in find_group_orlov()

min_clusters is signed integer and will be converted to unsigned
integer when compared with unsigned number stats.free_clusters.
If min_clusters is negative, it will be converted to a huge unsigned
value in which case all groups may not meet the actual desired free
clusters.
Set negative min_clusters to 0 to avoid unexpected behavior.

Fixes: ac27a0e ("[PATCH] ext4: initial copy of files from ext3")
Signed-off-by: Kemeng Shi <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>

Author: Kemeng Shi

fs/ext4/ialloc.c

@@ -514,6 +514,8 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent,
 	if (min_inodes < 1)
 		min_inodes = 1;
 	min_clusters = avefreec - EXT4_CLUSTERS_PER_GROUP(sb)*flex_size / 4;
+	if (min_clusters < 0)
+		min_clusters = 0;
 
 	/*
 	 * Start looking in the flex group where we last allocated an