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=1794662374; b=LDof0LC5B5v6vWn9CSTj4Vprct/nNyWOgGY71KIFBNt8rwDdeVwqP7K1afmds/Mrp3xe UTL1LtFIK2vO+kBPBu8qtjWjN1K4n/CS5clgYDF59VzAKWV3tDEsjj3OK9z8M4/yV+QUc TjTDsszkQgVVJJnOBtj5OuUvzGOKqT3NYQdTrKjdXX5rl0H4pWHLmxJbAmgo1b9EoH0Gh 2EDPYpGQG+wAhbyzPcg0y2vKxfSiDu/DnJ5s+sHCu+67W+xgvOwn2URYXJ2HqSNZERdGV 9eBUDpmx0WeS7K4HQLs55BqnvVDQP4QSMNY48qwRj3ub7E5qdPFMMGD6Fn/6JTcfWpA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794662374; h=Received:DKIM-Signature:Message-ID:From:Subject:Reply-To:To:Cc: In-Reply-To:References:Content-Type:Content-Transfer-Encoding:Date; bh=BppQier/no6YAbI2ELhYitnS9e2Uf7y91YG6Qn8f7X0=; b=AzQi//HRUnBzdISBdmG7AdsdqrWU0mHKp2016Fif5GHmJGrIaxbTE28SZBzsZTZWvyKL qZK3+5wEoUrG1owcPLDJDWWW4qkg7UYUvxSFrYsaBPAsJqOPwo/jBCrv4QIe5nxm/jDLM FD2vcNplDTGJRBfTO5X2VILTnPjN6lUON1Elvc8piUJTvay5iN00YcYtPqrYrpLREhgeW zGVE5jnsEMjy9p6nEUuI/EeuD2qAHU98C+3MeI8a7d8GHm3g/OgAAt3tma4Q+iUMUqxx4 9G9MbfkwtLk7EfmzSatquqhRCQ7+VRC2T1PHAKqgLEqZP/b6cRwhDt3cTLeW8VjwjhQ== 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=f8CPKR3i; 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 10B5B606A327; Sat, 14 Nov 2026 13:19:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=f8CPKR3i Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5D8961F000C4; Sat, 14 Nov 2026 13:19:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794662373; bh=BppQier/no6YAbI2ELhYitnS9e2Uf7y91YG6Qn8f7X0=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=f8CPKR3ijwUA9dhyqSibzYgkhQmoBHKbg4xgTC3gmJTV7Q5Yp/EWw+PjURxzhIgZl ya0qZwXe4uqL4OK1HC3F2vbPzvGKkLD1lom45yBvuxxVkU5tqn0XOy3OmA5+z2RU4U to/7o4Qy2HVaGHVyNwcP6H679kLm5A8KSWtB1idOKvmEILag3hbZi/u9ulm2XT2uNA UdHvghaneQIO3vKfx4FGJ/ALXsQUqiiiYn7UuRAhySfAmm7b17U4yZh8cTO/y2mY4i egSvfirioBNG7pluXubFCLzIx6GXsiqEXYbnsXFet19tbze5dB8l7rkMwoKN4HkzUm GbWfM8HJM1tyA== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [PATCH RFC v2 01/42] loop: refuse backing files that aren't open for reading Reply-To: sashiko-reviews@lists.linux.dev To: "Christian Brauner" Cc: linux-security-module@vger.kernel.org, selinux@vger.kernel.org, linux-s390@vger.kernel.org, linux-usb@vger.kernel.org, "Heiko Carstens" , "Vasily Gorbik" , "Alexander Gordeev" , "Christian Borntraeger" , "Mark Fasheh" , "Joel Becker" , "Joseph Qi" In-Reply-To: <20261114-work-loop-pseudo-v2-1-98639a2286fb@kernel.org> References: <20261114-work-loop-pseudo-v2-0-98639a2286fb@kernel.org> <20261114-work-loop-pseudo-v2-1-98639a2286fb@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Sat, 14 Nov 2026 13:19:33 +0000 X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list > loop_configure() takes any file as long as it implements ->read_iter(). > Loop itself never checked whether the file was actually opened for > reading. Buffered I/O went through vfs_iter_read() which refuses files > without FMODE_READ. Direct I/O has called ->read_iter() of the backing > file directly ever since loop grew support for it. >=20 > Since commit f2fed441c69b ("loop: stop using vfs_iter_{read,write} for > buffered I/O") buffered I/O calls ->read_iter() directly as well. That > commit was about O_DIRECT handling and the FMODE_READ check went away > as a side effect. >=20 > So whoever can set up a loop device can read a file it was only allowed > to open for writing. Open the file O_WRONLY, configure a loop device > with it and read the contents through the loop device. >=20 > Refuse backing files that aren't open for reading. Loop always reads > from its backing file so a write-only backing file never made sense in > the first place. >=20 > Fixes: bc07c10a3603 ("block: loop: support DIO & AIO") > Fixes: f2fed441c69b ("loop: stop using vfs_iter_{read,write} for buffered= I/O") > Cc: stable@vger.kernel.org > Reviewed-by: Jan Kara > Reviewed-by: Christoph Hellwig > Reviewed-by: Alexander Mikhalitsyn > Signed-off-by: Christian Brauner (Amutable) Sashiko has reviewed this patch and found no issues. --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261114-work-loop-= pseudo-v2-0-98639a2286fb@kernel.org?part=3D1