[PATCH] erofs-utils: lib: fix infinite loop on EOF in erofs_io_xcopy

[Lucas Karpinski]

On 2026-03-19 8:20 p.m., Ajay Rajera wrote:
> erofs_io_xcopy() has a fallback do-while loop for when the
> kernel fast-paths (copy_file_range/sendfile) do not handle all
> the data.  The loop does:
> 
>     ret = erofs_io_read(vin, buf, ret);
>     if (ret < 0)
>         return ret;
>     if (ret > 0) { ... pos += ret; }
>     len -= ret;
>   } while (len);
> 
> When erofs_io_read() returns 0 (EOF -- source exhausted before
> all bytes were copied), only the ret < 0 and ret > 0 branches
> were handled.  Since ret == 0, `len -= ret` is a no-op and
> `while (len)` stays true, causing the loop to spin forever at
> 100% CPU with no error and no progress.
> 
> This can be triggered when building an EROFS image from an input
> file that is shorter than expected -- e.g. a truncated source
> file, a pipe/FIFO that closes early, or a file being modified
> concurrently during mkfs.
> 
> Fix it by treating a zero return as an error (-ENODATA) so the
> caller fails cleanly instead of hanging indefinitely.
> 
> Also fix the long-standing 'pading' -> 'padding' typo in the
> short-read diagnostic message of erofs_dev_read().
> 
> Signed-off-by: Ajay Rajera <newajay.11r at gmail.com>
> ---
>  lib/io.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/lib/io.c b/lib/io.c
> index 0c5eb2c..583f52d 100644
> --- a/lib/io.c
> +++ b/lib/io.c
> @@ -430,7 +430,7 @@ ssize_t erofs_dev_read(struct erofs_sb_info *sbi, int device_id,
>  	if (read < 0)
>  		return read;
>  	if (read < len) {
> -		erofs_info("reach EOF of device @ %llu, pading with zeroes",
> +		erofs_info("reach EOF of device @ %llu, padding with zeroes",
>  			   offset | 0ULL);
>  		memset(buf + read, 0, len - read);
>  	}
> @@ -665,14 +665,15 @@ int erofs_io_xcopy(struct erofs_vfile *vout, off_t pos,
>  		int ret = min_t(unsigned int, len, sizeof(buf));
>  
>  		ret = erofs_io_read(vin, buf, ret);
> -		if (ret < 0)
> +		if (ret <= 0) {
> +			if (!ret)
> +				return -ENODATA;
>  			return ret;
> -		if (ret > 0) {
> -			ret = erofs_io_pwrite(vout, buf, pos, ret);

Change looks good to me, just minor nits.

Don't need the nested if and I think EIO would be better choice here
based on your description. We would expect to see 0 from erofs_io_read
when there is an issue with our input file, mostly caused by IO issues.

if (ret < 0)
	return ret;
else if (!ret)
	return -EIO;

ret = erofs_io_pwrite(vout, buf, pos, ret);

Regards,
Lucas Karpinski