Re: [edk2-devel] [PATCH] NetworkPkg/DxeNetLib: Change the order of conditions in IF statement

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Hi Zhang,

On 10/12/19 9:43 AM, Zhang, Shenglei wrote:
> The condition, NET_HEADSPACE(&(Nbuf->BlockOp[Index])) < Len, is meaningless
> if Index < 0. So 'Index < 0' should be performed first in the if statement.
> 
> Cc: Siyuan Fu <siyuan.fu@intel.com>
> Cc: Jiaxin Wu <jiaxin.wu@intel.com>
> Signed-off-by: Shenglei Zhang <shenglei.zhang@intel.com>
> ---
>   NetworkPkg/Library/DxeNetLib/NetBuffer.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/NetworkPkg/Library/DxeNetLib/NetBuffer.c b/NetworkPkg/Library/DxeNetLib/NetBuffer.c
> index 2408e9a10456..a35e67aa1f6c 100644
> --- a/NetworkPkg/Library/DxeNetLib/NetBuffer.c
> +++ b/NetworkPkg/Library/DxeNetLib/NetBuffer.c
> @@ -1063,7 +1063,7 @@ NetbufAllocSpace (
>       } else {
>         NetbufGetByte (Nbuf, 0, &Index);
>   
> -      if ((NET_HEADSPACE(&(Nbuf->BlockOp[Index])) < Len) && (Index > 0)) {
> +      if ((Index > 0) && (NET_HEADSPACE(&(Nbuf->BlockOp[Index])) < Len)) {

I'm not sure this is correct. Index is unsigned, so it won't be 
negative. NetbufGetByte() can set Index=0. With your change this case is 
not covered anymore.

Maybe your tool is unhappy because the return value of NetbufGetByte() 
isn't checked?

>           Index--;
>         }
>       }
>