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	Fri, 11 Sep 2026 16:09:28 +0000
Date: Fri, 11 Sep 2026 09:09:22 -0700
From: Breno Leitao <leitao@debian.org>
To: Stanislav Fomichev <sdf.kernel@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>, 
	Eric Dumazet <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>, 
	Paolo Abeni <pabeni@redhat.com>, Simon Horman <horms@kernel.org>, 
	Kuniyuki Iwashima <kuniyu@google.com>, Willem de Bruijn <willemb@google.com>, 
	David Ahern <dsahern@kernel.org>, Ido Schimmel <idosch@nvidia.com>, netdev@vger.kernel.org, 
	linux-kernel@vger.kernel.org, david.laight.linux@gmail.com, kernel-team@meta.com
Subject: Re: [PATCH net-next 1/2] net: add sockopt_expand_out()
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References: <20260910-getsockopt_phase6-v1-0-e681e102d5b8@debian.org>
 <20260910-getsockopt_phase6-v1-1-e681e102d5b8@debian.org>
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X-Debian-User: leitao

On Fri, Sep 11, 2026 at 08:56:23AM -0700, Stanislav Fomichev wrote:
> On 09/10, Breno Leitao wrote:
> >
> > +	if (size <= iov_iter_count(&opt->iter_out))
> > +		return 0;
> > +
> > +	if (WARN_ON_ONCE(!iter_is_ubuf(&opt->iter_out)))
> > +		return -EINVAL;
> 
> nit: if you end up re-spinning for some reason, maybe swap these two?

I am not sure we want to swap these two. This is the reason:

1) The first check (size <= iov_iter_count(&opt->iter_out)), check if we
   need the "hack" or not.

   a) If we don't need the tack, then we are fine and this could be called
      from user or kernel.
   
   b) for the hack (which happens in the next line -- iov_iter_ubuf()), it
      needs to be ubuf.

So, this force kernel callers to use the right optlen, avoiding hitting
the same issue as userspace.