Re: [PATCH] libfs: fix accidental overflow in offset calculation

[Al Viro]

On Fri, May 10, 2024 at 12:35:51AM +0000, Justin Stitt wrote:
> @@ -147,7 +147,9 @@ loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)
>  	struct dentry *dentry = file->f_path.dentry;
>  	switch (whence) {
>  		case 1:
> -			offset += file->f_pos;
> +			/* cannot represent offset with loff_t */
> +			if (check_add_overflow(offset, file->f_pos, &offset))
> +				return -EOVERFLOW;

Instead of -EINVAL it correctly returns in such cases?  Why?