From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6D96430C63B; Tue, 11 Aug 2026 15:15:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786461345; cv=none; b=lo73AbiBNIR3L04JIdMPnnqNEPY8cYuusVCJaHEThZuouDXqh/Qh5UMMmtfnia3CAT8/yb1KVoQ51IDpFXOGZp9bVZJzl/mmGnVpNlmAZ8zsN18+eNknvGDntUG15ZuBnO8cCHVniOX1ruJzGrdcCWeAHSvjhiEdEo9Qcys1xbg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786461345; c=relaxed/simple; bh=0W0i9LiGDxlOyNw906bbI2dfQkZTLP97Khq4p/vGNgc=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=KJ1dwjFzTe61uMlOp/jqIb1l4BsyZGbffq+8orQtcubVoWghGE0sOY4WUEdw4WYLvfmnAJoYDUhmUU1Wdla7itRjY+fFyfis7dgQ7Y2EB+kjfEEiNaVxIuswOQM/VUKpVdBMb4T3Ku68zAIBfUisKsK79E9DWda2Mn9zAWmL97s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=QINAOqwO; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="QINAOqwO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AC93C1F000E9; Tue, 11 Aug 2026 15:15:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786461344; bh=0W0i9LiGDxlOyNw906bbI2dfQkZTLP97Khq4p/vGNgc=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=QINAOqwO4s7waJHhE1InONiDEgxg5D3uMH6sw2gkasSbquf8oGPbnuaM2v+u78WT6 GHoxeP4Rb+QvC1UYlE1RuMDQvoUeEYeb06Li22mqxVxiOgYyC3QVPLcxnCO3gjFp3M /JTQ8P2MqCR63fmoLq/PBBWZVnHo6VD3VZdYSlrFExXQD96BaNUdFNMWgtgezaGWlR /zsuf71kI1QDmeug95bT6/9mke8ZsFX/PHIFSHz0DR9wX6gP5+WSdFocLoU6YgM6ER 0nIIKemH2oiddcB9Sg3zi87kreOjygPCQB21C9ueCoWsytLgnLayGIJZRS/2x9Q5s8 qu0gvgSkORYXQ== Date: Tue, 11 Aug 2026 08:15:43 -0700 From: Jakub Kicinski To: Breno Leitao Cc: David Laight , David Ahern , Ido Schimmel , "David S. Miller" , Eric Dumazet , Paolo Abeni , Simon Horman , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, stable@vger.kernel.org, Stanislav Fomichev Subject: Re: [PATCH net 1/2] ipv4: mcast: getsockopt: do not overwrite past optlen Message-ID: <20260811081543.26d18828@kernel.org> In-Reply-To: References: <20260806-mcast_fix-v1-0-bed0a5518e57@debian.org> <20260806-mcast_fix-v1-1-bed0a5518e57@debian.org> <20260807174402.2dfc12d6@pumpkin> <20260810222159.409357fa@pumpkin> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 11 Aug 2026 05:19:17 -0700 Breno Leitao wrote: > So my question to you: can you point me to actual software that > passes a "small" optlen and expects the kernel to write past it? That > would help to decide about the two options above. If you are very confident that no such SW exists - we can try to queue this up for -next. (TBH I'm not, mcast specifically may be full of strange one off manually written user space (as opposed to common libraries)). If we decide to change the behavior- we will probably have to wait until this makes it to an LTS release + some time for people to deploy. It can't be a fix. So practically speaking it may be more expedient to add some hacks to cater to this case in the conversion, and then remove the hack. That'd be easier to revert if someone pipes up later that we broke their SW.