Re: [patch] Use unsigned constants for ICMP6 filters [BZ #22489]

[Florian Weimer <fweimer@redhat.com>]

* DJ Delorie via Libc-alpha:

> Florian Weimer <fw@deneb.enyo.de> writes:
>> I'd say that the filter array *elements* are unsigned, but I don't
>> feel strongly about that.
>
> Ok, hopefully one last version and then we can paint the bike shed ;-)
>
> From 4ce3470246e0336e53010d66f30a1040a7e1f4bb Mon Sep 17 00:00:00 2001
> From: Sergey <s.korolev@ndmsystems.com>
> Date: Fri, 24 Apr 2020 17:18:41 -0400
> Subject: Use unsigned constants for ICMP6 filters [BZ #22489]
>
> The core problem here is that the filter array elements are unsigned
> but the computed constants are signed.  This both causes a
> signededness conversion at the &= step and may cause undefined
> behavior if the MSB is being modified.  This patch uses unsigned
> constants to avoid both cases. - DJ
>
> diff --git a/inet/netinet/icmp6.h b/inet/netinet/icmp6.h
> index a75722887d..5fed0fbca1 100644
> --- a/inet/netinet/icmp6.h
> +++ b/inet/netinet/icmp6.h
> @@ -85,16 +85,16 @@ struct icmp6_hdr
>  #define ICMP6_PARAMPROB_OPTION        2 /* unrecognized IPv6 option */
>  
>  #define ICMP6_FILTER_WILLPASS(type, filterp) \
> -	((((filterp)->icmp6_filt[(type) >> 5]) & (1 << ((type) & 31))) == 0)
> +	((((filterp)->icmp6_filt[(type) >> 5]) & (1U << ((type) & 31))) == 0)
>  
>  #define ICMP6_FILTER_WILLBLOCK(type, filterp) \
> -	((((filterp)->icmp6_filt[(type) >> 5]) & (1 << ((type) & 31))) != 0)
> +	((((filterp)->icmp6_filt[(type) >> 5]) & (1U << ((type) & 31))) != 0)
>  
>  #define ICMP6_FILTER_SETPASS(type, filterp) \
> -	((((filterp)->icmp6_filt[(type) >> 5]) &= ~(1 << ((type) & 31))))
> +	((((filterp)->icmp6_filt[(type) >> 5]) &= ~(1U << ((type) & 31))))
>  
>  #define ICMP6_FILTER_SETBLOCK(type, filterp) \
> -	((((filterp)->icmp6_filt[(type) >> 5]) |=  (1 << ((type) & 31))))
> +	((((filterp)->icmp6_filt[(type) >> 5]) |=  (1U << ((type) & 31))))
>  
>  #define ICMP6_FILTER_SETPASSALL(filterp) \
>  	memset (filterp, 0, sizeof (struct icmp6_filter));

Looks good to me know.

Reviewed-by: Florian Weimer <fweimer@redhat.com>

Thanks,
Florian