From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <56B24F95.9040702@codeaurora.org> Date: Wed, 03 Feb 2016 11:05:57 -0800 From: Nikhilesh Reddy MIME-Version: 1.0 To: Jann Horn CC: torvalds@linux-foundation.org, Miklos Szeredi , fuse-devel , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, gregkh@linuxfoundation.org, linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, Richard Weinberger , Theodore Ts'o , jack@suse.cz, Antonio SJ Musumeci , sven.utcke@gmx.de, Nikolaus Rath , Jann Horn , Mike Shal Subject: Re: [PATCH v5] fuse: Add support for passthrough read/write References: <56AFAA5B.3000006@codeaurora.org> <20160202081035.GA18246@pc.thejh.net> In-Reply-To: <20160202081035.GA18246@pc.thejh.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: Hi Thanks for your review again :) > > Uh... how do you know at this point that the file is actually writable? > Normally, e.g. vfs_write() will ensure that the file is writable, and > e.g. generic_file_write_iter() won't check for writability as far as I > can tell. This might allow someone to use the passthrough mechanism to > overwrite a file he is only allowed to read, but not write, like > /etc/passwd. I considered adding the checks ( the same ones that VFS does) but not sure if we need to. So the user will need to construct a fuse filesystem ( that opens for O_READONLY even though the user asks for a O_RDWR from the FUSE open) and then mount it , with CAP_SYS_ADMIN for which you need to be root but once he has that he should be able to easily get to the files without needing to go through FUSE right using CAP_DAC_OVERRIDE? Am i missing something? Please do help me understand. But yes if really needed I can add additional checks once i understand it > > Also, I think this might bypass mandatory locks, the > security_file_permission hook (which seems like a bad idea anyway > though), inotify/fsnotify and sb_start_write. > Can you please elaborate/clarify further? I am am not sure what you mean. Again thanks for your reviews :) Appreciate your help -- Thanks Nikhilesh Reddy Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.