quota: Don't overflow quota file offsets

The on-disk quota format supports quota files with upto 2^32 blocks. Be
careful when computing quota file offsets in the quota files from block
numbers as they can overflow 32-bit types. Since quota files larger than
4GB would require ~26 millions of quota users, this is mostly a
theoretical concern now but better be careful, fuzzers would find the
problem sooner or later anyway...
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/quota/quota_tree.c

@@ -62,7 +62,7 @@ static ssize_t read_blk(struct qtree_mem_dqinfo *info, uint blk, char *buf)
 
 	memset(buf, 0, info->dqi_usable_bs);
 	return sb->s_op->quota_read(sb, info->dqi_type, buf,
-	       info->dqi_usable_bs, blk << info->dqi_blocksize_bits);
+	       info->dqi_usable_bs, (loff_t)blk << info->dqi_blocksize_bits);
 }
 
 static ssize_t write_blk(struct qtree_mem_dqinfo *info, uint blk, char *buf)
@@ -71,7 +71,7 @@ static ssize_t write_blk(struct qtree_mem_dqinfo *info, uint blk, char *buf)
 	ssize_t ret;
 
 	ret = sb->s_op->quota_write(sb, info->dqi_type, buf,
-	       info->dqi_usable_bs, blk << info->dqi_blocksize_bits);
+	       info->dqi_usable_bs, (loff_t)blk << info->dqi_blocksize_bits);
 	if (ret != info->dqi_usable_bs) {
 		quota_error(sb, "dquota write failed");
 		if (ret >= 0)
@@ -284,7 +284,7 @@ static uint find_free_dqentry(struct qtree_mem_dqinfo *info,
 			    blk);
 		goto out_buf;
 	}
-	dquot->dq_off = (blk << info->dqi_blocksize_bits) +
+	dquot->dq_off = ((loff_t)blk << info->dqi_blocksize_bits) +
 			sizeof(struct qt_disk_dqdbheader) +
 			i * info->dqi_entry_size;
 	kfree(buf);
@@ -559,7 +559,7 @@ static loff_t find_block_dqentry(struct qtree_mem_dqinfo *info,
 		ret = -EIO;
 		goto out_buf;
 	} else {
-		ret = (blk << info->dqi_blocksize_bits) + sizeof(struct
+		ret = ((loff_t)blk << info->dqi_blocksize_bits) + sizeof(struct
 		  qt_disk_dqdbheader) + i * info->dqi_entry_size;
 	}
 out_buf: