From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [78.32.30.218]) (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 46D4929B77C for ; Sun, 28 Jun 2026 23:17:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=78.32.30.218 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782688632; cv=none; b=sL6NmzgmXUevK5RpoFDJjbGqncNQFzE7HELR+nnA6K72tTNkd/hIYyKUz5vWezdWLHKwi2BsHZsBFyETbgypLJK7EdrjSUwZenTJiXoO4wlqQrvKnmsLQ8H0DURZZBLiyvwLVrWwbL+ISRwgqyPDzYPqQh44S5lWCgBvtLIlT8w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782688632; c=relaxed/simple; bh=ftd4xdNIxb24Twr3Xaq9d7KDpXrdZMyVrh3s+vXVYC8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=CBaPdfEAiXvqtwfF5G4donXnofO/plD+QhkI5Ps2mx7j+DDziZlUz7Pavp88L9A+baGnIoiyQsqO4raP8L9lN7TWHTHcbwBDnO4wGw+lzl69oeheno9u0V2LXd1P5Hy3grQIL1iXT5MUD/IqNDp7m0+8p7rrKaNHwUq8hH845Y0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=armlinux.org.uk; spf=none smtp.mailfrom=armlinux.org.uk; dkim=pass (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b=iiKuPAnH; arc=none smtp.client-ip=78.32.30.218 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=armlinux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=armlinux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b="iiKuPAnH" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=yFEakxea6i8xyEof4fcw01AG5K9WSCL+9WsJ/kzlexA=; b=iiKuPAnHLRfyUUh+rz4Yd5JHQZ +UQegHO757XyQtebnI7vec9MZpFlpodgxgE2YXLcD+hzJ3n/fc9tZTqUJv0mdTZODWcn468u2PP3X dV9h9jENclEM9D+FCs9mNiicJP3jPMa+lJLRsEfewcSX4OiJ4Gge+4l/tmN57TsvyUZMNKHRNrOoc TEtaFotlC/KnC1X5Wzm1z6XXJPY7aubY9hpypRJ2KUMaQ4uPjnX+ofJdIwLgx9IBtwcMf5L6HT3FZ bxWAyU7++tdaxZ1UVpOyK8nx2hzeCZ6lRtT2KIV6rCqoFOsCs7zcsqIsSK/pzStmdMStys/uLOwa1 GYQhTuFQ==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:50312) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.98.2) (envelope-from ) id 1wdykE-000000004Uo-1EL4; Mon, 29 Jun 2026 00:16:58 +0100 Received: from linux by shell.armlinux.org.uk with local (Exim 4.98.2) (envelope-from ) id 1wdykC-000000005LV-2YKG; Mon, 29 Jun 2026 00:16:56 +0100 Date: Mon, 29 Jun 2026 00:16:56 +0100 From: Russell King To: Samuel Moelius Cc: kees@kernel.org, brauner@kernel.org, iwasbaeyz@gmail.com, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk Subject: Re: [PATCH v2 1/2] adfs: reject disc records smaller than one filesystem block Message-ID: References: <202606101323.0DFB06B054@keescook> <20260628220126.94212-1-sam.moelius@trailofbits.com> <20260628220126.94212-2-sam.moelius@trailofbits.com> 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-Disposition: inline In-Reply-To: <20260628220126.94212-2-sam.moelius@trailofbits.com> Sender: "Russell King,,," On Sun, Jun 28, 2026 at 10:01:25PM +0000, Samuel Moelius wrote: > ADFS uses the on-disk disc size to report statfs block counts. The disc > record validator checks the sector size, id length, high disc-size bits, > map zone count, and reserved bytes, but it accepts a declared disc size > smaller than one filesystem block. > > A crafted one-zone image with log2secsize 9 and disc_size 1 can pass map > checksum validation and mount. A subsequent statfs then reports zero > f_blocks from adfs_map_statfs(), and adfs_statfs() divides by that zero > while deriving f_ffree. I think this is still too low. 1. The disc map is nzones sectors long, and can not be in the same sector as the boot block. The disc record can not share with the map. This means the minimum is 1 + nzones sectors to fit just the map in. 2. If the disc record was found at 0xc00 rather than 0, then that will add sectors to the minimum size. 3. The root directory is also necessary, which is 2048 bytes for an E/F format (format_version=0) or root_size for an F+ format. So, if we're really trying to avoid mounting something that isn't a proper image, then just checking that the disc size is at least one sector isn't sufficient. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!