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=1792699897; b=3IH+rkz0N23GhOjj9e+HmgdnuuwfGFK51Po4B1zX6JD5LB6I91tenYkC2BRCnPu5rUB+ FFZOb3Vx4HvuOMaaZ4w9nh0zVYqyvXRyTByWylhTskK+PDL0HZwJAkgbwa4OP4F0rGlGT BGpk5CKKO7kkfgWQrpOczpgDqwYSB1tPyC2Tf9xIhNkQHt/LQbkHR3UdMfSi77Sq/uyjF J050jfsOCvnp/jk+OGRm7bPhdJ9Yatwyuaa0Cid7e0iiBFZ4VvKC2zo5HL2xVYucBomgU 1eDtv5OmEzLzGXUAmmgBMqolNd96cPTJzhGtM/d3sfeDUEVTKTfxNM9W4dzGWu7jZSw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792699897; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=8YeXKojMVZ/QKBEred3exRdn/k0MseRHZQRqTCQsT7E=; b=xnFsYnYXMzN3ppqrKBHfwjEj6vMS9sO9ceRG9EcsLm3VSNjZ1rnvMQRt28h2XJ5fmk9w NAKVW6I7PcnW9ogwDe14/FLdu7SRcfSvJPUtoMLD6tkkgmiuEEmBiEXIhbmrrcp0X3Uus 5ESBhcbwupLKgPZ11jsDJCi7MQj5ja8O5RgaEJM2MMtZQEJQN9DAH0CcGYZvOHS5M2frU TAd+BlwjLRQae1n6/CGuuZn0h2Z8a/3kswqVDm9TxsfnLVMhQlBMVYx6ia+/ncK0xEz+J r10y1YQ58hJEuHLKuM0PuH3XSg3Qt5UnrK5kA9Dh2N0n9XXQ/9SbcfqYSRBVu/Iwnsg== 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="NnZIkso/"; 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 8AA77606A31A; Thu, 22 Oct 2026 20:11:37 +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=NnZIkso/ Received: by smtp.kernel.org (Postfix) with ESMTPSA id 48FEC1F031E1; Thu, 22 Oct 2026 20:11:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792699897; bh=8YeXKojMVZ/QKBEred3exRdn/k0MseRHZQRqTCQsT7E=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=NnZIkso/2KXBoi6qMcQQ3e+73LkZkQeYI7tFin4B6XbQ+I4zuXxMPPRYK/DT2z6nh bcEboRefE3QneNNz75zbr8DF3OxFDAxLtWnagYAvV3Z7vYAir3z9DkbEdSDgEl0X0g lPQ0OvmQXJHR1M3QgoBKAC2f6da3Vm5+8+/dnM1UVvPa6ukuVBLdwMgJbvgaD6wIQ+ K7t8fXzHobtdBH7VlPbX9HWHbodbBHNOASX6+H1CYDmRHXv+KIPgyS/IbRLL3sXc8M 6rliNs5t88hbu0GJN5jX7UT14Szh8/XrmcMzMnGV2QOrXdEttGVFrySLx56KJCT1zH xxrxhCaCfmSow== Date: Thu, 22 Oct 2026 22:11:27 +0200 From: Alejandro Colomar To: Steven Rostedt Cc: Kees Cook , Bill Wendling , "Matthew Wilcox (Oracle)" , Andrew Morton , Andy Shevchenko , David Gow , Petr Mladek , Shuvam Pandey , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v5 06/12] seq_buf: Add seq_buf_strlen() Message-ID: References: <20261005155653.late.426-kees@kernel.org> <20261005155708.1471260-6-kees@kernel.org> <20261016145928.16eddc9a@gandalf.local.home> <202610221058.C5626C5172@keescook> <20261022155726.7f20c4cb@gandalf.local.home> 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: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="74wc3amtt2nanemr" Content-Disposition: inline In-Reply-To: <20261022155726.7f20c4cb@gandalf.local.home> --74wc3amtt2nanemr Content-Type: text/plain; protected-headers=v1; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable From: Alejandro Colomar To: Steven Rostedt Cc: Kees Cook , Bill Wendling , "Matthew Wilcox (Oracle)" , Andrew Morton , Andy Shevchenko , David Gow , Petr Mladek , Shuvam Pandey , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v5 06/12] seq_buf: Add seq_buf_strlen() Message-ID: References: <20261005155653.late.426-kees@kernel.org> <20261005155708.1471260-6-kees@kernel.org> <20261016145928.16eddc9a@gandalf.local.home> <202610221058.C5626C5172@keescook> <20261022155726.7f20c4cb@gandalf.local.home> MIME-Version: 1.0 In-Reply-To: <20261022155726.7f20c4cb@gandalf.local.home> Hi Steven, > Date: 2026-10-22 15:57:51-0400 > From: Steven Rostedt > > On Thu, 22 Oct 2026 21:41:53 +0200 > Alejandro Colomar wrote: >=20 > > > > Hmm, I just realized that this could inadvertently overflow the buf= fer. If > > > > len =3D=3D size, it may not be overflowed. If using seq_buf_putmem(= ) and > > > > filling the entire buffer, calling this would force an overflow as = we just > > > > truncated the last byte. =20 > > >=20 > > > Hm, yes. So the "else" branch needs to include: > > >=20 > > > s->len =3D s->size + 1; =20 > >=20 > > Please think again about the possibility of using pointers instead of > > lengths. This is a source of off-by-one bugs that's only caused by > > the choice of data, I believe. If using pointers, truncation would be > > stored as a NULL pointer, and off-by-ones would be less likely. > >=20 > > Consider this off-by-one to be just a sympthom of the underlying > > problematic design. Whenever a design forces you to write +1 or -1, > > there are high chances that the design is sub-optimal regarding safety. >=20 > It's not an off-by-one error here. The s->len =3D size - 1 is correct, bu= t it > also has a side effect of removing a character without marking it > overflowed. It's correct, but at the same time an opportunity for off-by-one mistakes. > The seq_buf defines being "overflowed" as s->len =3D=3D s->size + 1. > What the else statement should have is: >=20 > else > seq_buf_set_overflow(s); >=20 > Which would be less confusing to reviewers as that is defined as: >=20 > static inline void > seq_buf_set_overflow(struct seq_buf *s) > { > s->len =3D s->size + 1; > } Agree. But still, a better design would do: static inline void seq_buf_set_overflow(struct seq_buf *s) { s->p =3D NULL; } This is way more robust, and also easier to understand. My head is boiling when trying to review this patch set for correctness. That's not a good sign. Have a lovely night! Alex >=20 > -- Steve --=20 --74wc3amtt2nanemr Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEES7Jt9u9GbmlWADAi64mZXMKQwqkFAmrabegACgkQ64mZXMKQ wqmu5Q//Wfe63wcUcEFjGLtX0Hv7/Frnxp/TzsOySg7UPJ+7DDOTz+Klx7Fl/Ue7 dsoRh/uEkhLc6LRdcl8akPcAo8b+/Vn5TQbOPeG+DpgR5xvSs/XJuF9IxyVN4oh2 zIZm1iEJcCQjCYvQF+ecNtDPrY4fvkq3Sueg4xLc84+LU7kzS+JenJPQYf+JgDd/ tuiPDBbyhOLNiZZtqt7Nm4VVbB1RVgZG8Ze2Rtjwr0wrvBgqHzvqb1SyjX2oKgp4 pTd52gck2wDUdVqTxWEA61+J57y5ElA/NiykkObyr3MkhSVEULUVaYa1/n/6vT0D R9biVwM5AnvadaMKC6tjd603jemFT2G4oONJJ68eZcgQVHTYr8/Y4LPZllajg3tw uORuak9XpeOzCRhCiTTJhOumQqp9qRWe90PFbmAfmxz1hkceb/n1XMzR+oRzOqRZ MnyV0eEhSPosUMqEVWgtBimlht4w8m5S/UoQ5fW4eOt1vGYAij0I2ctKHeV3dGlr X6430dgoeL3KRHRVBwONXLWiRyIHWQ5h+6gPco7QaXnfRzM1K/GRtfVX3ovlq4Nj V1xeTRv1gUhcUKr2lPGQMVqetaq2/EWwSXKTl2cX/UQOY3spj8uK1kkMCFA8czZb Zbzxk9P08GvYp1Tfm71LLAN1NoAYtcNtMYaas6bMph0RzcllWXY= =WWyU -----END PGP SIGNATURE----- --74wc3amtt2nanemr--