From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793468892; b=Onii3zYNvxDdZRS5OGHfuhSnCYOWoiiDj4baytp/BgjANgUQrCrEdKOMkuGG9gHO+i7M EeZWql3SAg4I31rxEWHeBi+laVbK8mJYpi+x2DmyerSIqPZAn1vGVRluQHNtsvngMvTiJ xXjENLdfJHP1cyGoCZFqIrt+kf2QNfQyNUiYppXG9j/ILDD0Ry1Eu+oK4cv/oXjUmmHCy F6waj4DTrbBkKSABkqrgD0ApVcIEWQayCt4wzava/eh82mFVPIXdh2M9gigaS1792KGWd G4Z0oCviUTbMH62ZF/w9kGYSXcGs2HJ4wpiaZKj33R3EBkoHw1v6/PJeDl2IEoNqP0w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793468892; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=ijyk755RKB9PH7Ivb9JZ9BkwDVCr81ydGZssI4CFSRs=; b=clSmc0RZTcrjmYotIi6anwaCQMJJ6dPgof2yTv5w5VF2+0frUGzfOMAXfoY/InAFxmKL zEkwshgitNXvcS1ajeLcWOno0FPiXKeq4B7Jhzn6gHFn87PZfIJPRtr2IcGpAv+ODju+E DJ1cLsY9IIJ8h3oM+zLULom0dQzG3rYZR+X92jpAdxu33KmaDvSF8MwcrYG/KRg/QKCSk kfpKMHcu/JEyqaK0kmwfp4mZ6xJJLr3+JKraxuuo3PBwnRq5bdOcTZJ2OWz11csi5m6Xv CTyLqzXOr/y0MM6Qg1T4OVWECrku0w/GCd1hdmyGcP4hZNwRF+c/N9hJc8lzAz03HTg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=la2vvVQR; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7F205606A31C; Sat, 31 Oct 2026 17:48:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=la2vvVQR Received: by smtp.kernel.org (Postfix) with ESMTPSA id 218611F000C1; Sat, 31 Oct 2026 17:48:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793468892; bh=ijyk755RKB9PH7Ivb9JZ9BkwDVCr81ydGZssI4CFSRs=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=la2vvVQRE8Z6QHAsCS0fKIzAKtPb+FEGjiQ48EUiVneGviCjka8mkeMQpPKyEU93A S9gEf20u97yU8JnPvLfu9UngWuC0GPVoxEjkabpjbsuOdQdNqkXEBUG92yuqsU+Bdb MGhctkHvgDU6EmGFfWUVtwnUEU4M8qEWW0TpZ8PNI4nr0BBBvKRu3Si1YMJ/Q/MVCW 6UgKUNjyFOD48SH+G+NxiqQxPG9lcj1OnuV6irc+qxuF4eN3yrLc8zU5uvVtN81RGi E6W+YZV7BzCzDCebZTN8HzyfhylhtoaUEjMdNqggPJ9iDtRif/7bSYKOZRLyYI40HS mVv7TzrFt4iQg== Date: Sat, 31 Oct 2026 17:48:07 +0000 From: Simon Horman To: Qingfang Deng Cc: netdev-bot+sashiko@kernel.org, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@kernel.org, kuba@kernel.org, pabeni@redhat.com, leitao@debian.org, norbert@doyensec.com, hataegu0826@gmail.com, paulus@ozlabs.org, Brice.Goglin@ens-lyon.org, akpm@osdl.org, Matt_Domsch@dell.com, linux-ppp@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net] ppp: remove SC_MUST_COMP Message-ID: <20261031174807.GS257209@horms.kernel.org> References: <20261029074935.40509-1-qingfang.deng@linux.dev> <179339596607.3131.10030375792154782283@kernel.org> <84396bab-166b-435f-9663-0aa2939de3fc@linux.dev> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <84396bab-166b-435f-9663-0aa2939de3fc@linux.dev> On Sat, Oct 31, 2026 at 09:28:10AM +0800, Qingfang Deng wrote: > On 10/31/2026 5:32 AM, netdev-bot+sashiko@kernel.org wrote: > > [Severity: Medium] > > Does the fix need the define to be removed from the UAPI header? > > > > PPPIOCSFLAGS already masks the user value with the kernel-internal > > SC_FLAG_BITS: > > > > drivers/net/ppp/ppp_generic.c:ppp_ioctl() { > > ... > > ppp->flags = val & SC_FLAG_BITS; > > ... > > } > > > > Removing the bit from SC_FLAG_BITS (and SC_MASK), together with the two > > checks, looks like enough to stop SC_DC_ERROR from being stored as a > > config flag. > > > > Deleting the define is a separate change at the source level. Userspace > > that includes , directly or through , > > and refers to SC_MUST_COMP would no longer build. > > > > The commit message calls the flag unused, but the evidence is that one > > pppd integration from 2005 never landed upstream. That does not rule out > > out-of-tree pppd MPPE forks or other daemons that use the name. > > > > With the Fixes: tag pointing at a 2005 commit, this header change will > > likely be backported to the stable kernel-headers as well. > > > > Would it work to keep the define, with a comment that the kernel ignores > > it and that it aliases SC_DC_ERROR, while still dropping it from > > SC_FLAG_BITS and SC_MASK and removing the checks? > > I found no trace of existing users (searched GitHub). Even _if_ there are > any, _and_ SC_MUST_COMP does not alias SC_DC_ERROR, the logic is still > flawed - received packets are silently dropped without noticing the > userspace. > > If the goal is to prevent the removal from backports, I may split out the > removal part into a net-next patch. I lean towards your existing approach: it's broken, and that brought to the attention of any user of it. Reviewed-by: Simon Horman