Subject: Re: [PATCH net] ipv4: clamp MCAST_MSFILTER getsockopt to optlen, not gf_numsrc

From: Greg Kroah-Hartman <[email-masked]>
Date: Thu, 23 Apr 2026 17:06:42 +0200

On Thu, Apr 23, 2026 at 04:29:06PM +0200, Paolo Abeni wrote:
> On 4/23/26 4:18 PM, Greg Kroah-Hartman wrote:
> > On Thu, Apr 23, 2026 at 03:57:55PM +0200, Paolo Abeni wrote:
> >> On 4/20/26 9:26 PM, Greg Kroah-Hartman wrote:
> >>> @@ -1486,8 +1491,12 @@ static int compat_ip_get_mcast_msfilter(struct sock *sk, sockptr_t optval,
> >>>  	gf.gf_interface = gf32.gf_interface;
> >>>  	gf.gf_fmode = gf32.gf_fmode;
> >>>  	num = gf.gf_numsrc = gf32.gf_numsrc;
> >>> -	gf.gf_group = gf32.gf_group;
> >>>  
> >>> +	if (num > (len - size0) / sizeof(struct sockaddr_storage))
> >>> +		num = (len - size0) / sizeof(struct sockaddr_storage);
> >>> +	gf.gf_numsrc = num;
> >>
> >> Since this is exactly the same code added above, likely a common helper
> >> would be useful.
> > 
> > Useful where else?
> 
> Just in these 2 functions, to avoid duplicating the logic.
> 
> Not a big deal, but it would feel nicer. Also the
> 
> 	gf.gf_group = gf32.gf_group;
> 
> statement is moved around but such change is not needed, right?

It's just moved down, I inserted the check/assignment before that line,
and git diff shows that as remove/add for some reason :(

thansk,

greg k-h