Re: [PATCH] SUNRPC: xdrgen: Initialize data pointer for zero-length items

[Jeff Layton <jlayton@kernel.org>]

On Sat, 2025-12-20 at 10:41 -0500, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> The xdrgen decoders for strings and opaque data had an
> optimization that skipped calling xdr_inline_decode() when the
> item length was zero. This left the data pointer uninitialized,
> which could lead to unpredictable behavior when callers access
> it.
> 
> Remove the zero-length check and always call xdr_inline_decode().
> When passed a length of zero, xdr_inline_decode() returns the
> current buffer position, which is valid and matches the behavior
> of hand-coded XDR decoders throughout the kernel.
> 
> Fixes: 4b132aacb076 ("tools: Add xdrgen")
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  include/linux/sunrpc/xdrgen/_builtins.h | 20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/sunrpc/xdrgen/_builtins.h b/include/linux/sunrpc/xdrgen/_builtins.h
> index 52ed9a9151c4..a723fb1da9c8 100644
> --- a/include/linux/sunrpc/xdrgen/_builtins.h
> +++ b/include/linux/sunrpc/xdrgen/_builtins.h
> @@ -248,12 +248,10 @@ xdrgen_decode_string(struct xdr_stream *xdr, string *ptr, u32 maxlen)
>  		return false;
>  	if (unlikely(maxlen && len > maxlen))
>  		return false;
> -	if (len != 0) {
> -		p = xdr_inline_decode(xdr, len);
> -		if (unlikely(!p))
> -			return false;
> -		ptr->data = (unsigned char *)p;
> -	}
> +	p = xdr_inline_decode(xdr, len);
> +	if (unlikely(!p))
> +		return false;
> +	ptr->data = (unsigned char *)p;
>  	ptr->len = len;
>  	return true;
>  }
> @@ -279,12 +277,10 @@ xdrgen_decode_opaque(struct xdr_stream *xdr, opaque *ptr, u32 maxlen)
>  		return false;
>  	if (unlikely(maxlen && len > maxlen))
>  		return false;
> -	if (len != 0) {
> -		p = xdr_inline_decode(xdr, len);
> -		if (unlikely(!p))
> -			return false;
> -		ptr->data = (u8 *)p;
> -	}
> +	p = xdr_inline_decode(xdr, len);
> +	if (unlikely(!p))
> +		return false;
> +	ptr->data = (u8 *)p;
>  	ptr->len = len;
>  	return true;
>  }

Reviewed-by: Jeff Layton <jlayton@kernel.org>