Re: [PATCH net-next 2/2] ipv4: igmp: convert ip_mc_msfget() to sockopt_t

[Stanislav Fomichev <sdf.kernel@gmail.com>]

On 09/10, Breno Leitao wrote:
> IP_MSFILTER reads its reply through ip_mc_msfget(), reached from
> do_ip_getsockopt() and from nowhere else. Convert it, and build the
> sockopt_t at the call site for as long as the caller still carries a
> sockptr_t pair.
> 
> This is a special case, where optlen might only point
> to the header, and the real structure size is inside the header.
> 
> This is nasty, but, in order to avoid breaking userspace, we need to
> preserve the same mechanism, by:
> 
> 1) Only applying it for userspace address, otherwise it is too risky
> 2) Assume there is room to support the new size (in userspace)
> 
> The source list also moves from copy_to_sockptr_offset() to a sequential
> copy_to_iter(). IP_MSFILTER_SIZE(0) and offsetof(struct ip_msfilter,
> imsf_slist_flex) are both 16, so the bytes land where they did.
> 
> Signed-off-by: Breno Leitao <leitao@debian.org>

Acked-by: Stanislav Fomichev <sdf@fomichev.me>