[PATCH] erofs-utils: fuse: fix random readlink error

[Gao Xiang]

Hi Weiwen,

On Fri, Jan 22, 2021 at 12:31:43AM +0800, Hu Weiwen wrote:
> readlink should fill a **null terminated** string in buffer.
> 
> Also, read should return number of bytes remaining on EOF.
> 
> Link: https://lore.kernel.org/linux-erofs/20210121101233.GC6680@DESKTOP-N4CECTO.huww98.cn/
> Signed-off-by: Hu Weiwen <sehuww at mail.scut.edu.cn>

Thanks for catching this!

> ---
>  fuse/main.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/fuse/main.c b/fuse/main.c
> index c162912..bc1e496 100644
> --- a/fuse/main.c
> +++ b/fuse/main.c
> @@ -71,6 +71,12 @@ static int erofsfuse_read(const char *path, char *buffer,
>  	if (ret)
>  		return ret;
>  
> +	if (offset >= vi.i_size)
> +		return 0;
> +
> +	if (offset + size > vi.i_size)
> +		size = vi.i_size - offset;
> +

It would be better to call erofs_pread() with the original offset
and size (also I think there is some missing memset(0) for
!EROFS_MAP_MAPPED), and fix up the return value to the needed value.

Thanks,
Gao Xiang

>  	ret = erofs_pread(&vi, buffer, size, offset);
>  	if (ret)
>  		return ret;
> @@ -79,10 +85,16 @@ static int erofsfuse_read(const char *path, char *buffer,
>  
>  static int erofsfuse_readlink(const char *path, char *buffer, size_t size)
>  {
> -	int ret = erofsfuse_read(path, buffer, size, 0, NULL);
> +	int ret;
> +	size_t path_len;
> +
> +	erofs_dbg("path:%s size=%zd", path, size);
> +	ret = erofsfuse_read(path, buffer, size, 0, NULL);
>  
>  	if (ret < 0)
>  		return ret;
> +	path_len = min(size - 1, (size_t)ret);
> +	buffer[path_len] = '\0';
>  	return 0;
>  }
>  
> -- 
> 2.30.0
>