Re: [PATCH] SUNRPC: clean up integer overflow check

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On Fri, 2023-06-30 at 12:46 +0300, Dan Carpenter wrote:
> This integer overflow check works as intended but Clang and GCC and warn
> about it when compiling with W=1.
> 
>     include/linux/sunrpc/xdr.h:539:17: error: comparison is always false
>     due to limited range of data type [-Werror=type-limits]
> 
> Use size_mul() to prevent the integer overflow.  It silences the warning
> and it's cleaner as well.
> 
> Reported-by: Dmitry Antipov <dmantipov@xxxxxxxxx>
> Closes: https://lore.kernel.org/all/20230601143332.255312-1-dmantipov@xxxxxxxxx/
> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> ---
> Btw, since the Clang developers are automatically CC'd, here is how I
> silenced this type of false positive in Smatch:
> 
> 1) Check that longs are 64 bit.
> 2) Check that the right hand side has a SIZE_MAX.  SIZE_MAX is defined
>    as -1UL so you want both the type and the value to match.
> 3) Then on the other the other side, check that the type is uint.
> 
> I'm looking at this code now in Smatch and it's kind of ugly, and also
> there are some other places where I need to apply the same logic...
> 
>  include/linux/sunrpc/xdr.h | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/include/linux/sunrpc/xdr.h b/include/linux/sunrpc/xdr.h
> index f89ec4b5ea16..dbf7620a2853 100644
> --- a/include/linux/sunrpc/xdr.h
> +++ b/include/linux/sunrpc/xdr.h
> @@ -775,9 +775,7 @@ xdr_stream_decode_uint32_array(struct xdr_stream *xdr,
>  
>  	if (unlikely(xdr_stream_decode_u32(xdr, &len) < 0))
>  		return -EBADMSG;
> -	if (len > SIZE_MAX / sizeof(*p))
> -		return -EBADMSG;
> -	p = xdr_inline_decode(xdr, len * sizeof(*p));
> +	p = xdr_inline_decode(xdr, size_mul(len, sizeof(*p)));
>  	if (unlikely(!p))
>  		return -EBADMSG;
>  	if (array == NULL)


Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>




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