From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg Kroah-Hartman Subject: Re: [PATCH 0/6] File Sealing & memfd_create() Date: Wed, 19 Mar 2014 19:55:30 -0700 Message-ID: <20140320025530.GA25469@kroah.com> References: <1395256011-2423-1-git-send-email-dh.herrmann@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Matthew Wilcox , Ryan Lortie , Hugh Dickins , Kay Sievers , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Daniel Mack , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Karol Lewandowski , Lennart Poettering , Johannes Weiner , Tejun Heo , "Michael Kerrisk \(man-pages\)" , Andrew Morton , Linus Torvalds , Alexander Viro To: David Herrmann Return-path: Content-Disposition: inline In-Reply-To: <1395256011-2423-1-git-send-email-dh.herrmann@gmail.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" List-Id: linux-fsdevel.vger.kernel.org On Wed, Mar 19, 2014 at 08:06:45PM +0100, David Herrmann wrote: > Hi > > This series introduces the concept of "file sealing". Sealing a file restricts > the set of allowed operations on the file in question. Multiple seals are > defined and each seal will cause a different set of operations to return EPERM > if it is set. The following seals are introduced: > > * SEAL_SHRINK: If set, the inode size cannot be reduced > * SEAL_GROW: If set, the inode size cannot be increased > * SEAL_WRITE: If set, the file content cannot be modified > > Unlike existing techniques that provide similar protection, sealing allows > file-sharing without any trust-relationship. This is enforced by rejecting seal > modifications if you don't own an exclusive reference to the given file. So if > you own a file-descriptor, you can be sure that no-one besides you can modify > the seals on the given file. This allows mapping shared files from untrusted > parties without the fear of the file getting truncated or modified by an > attacker. > > Several use-cases exist that could make great use of sealing: > > 1) Graphics Compositors > If a graphics client creates a memory-backed render-buffer and passes a > file-decsriptor to it to the graphics server for display, the server > _has_ to setup SIGBUS handlers whenever mapping the given file. Otherwise, > the client might run ftruncate() or O_TRUNC on the on file in parallel, > thus crashing the server. > With sealing, a compositor can reject any incoming file-descriptor that > does _not_ have SEAL_SHRINK set. This way, any memory-mappings are > guaranteed to stay accessible. Furthermore, we still allow clients to > increase the buffer-size in case they want to resize the render-buffer for > the next frame. We also allow parallel writes so the client can render new > frames into the same buffer (client is responsible of never rendering into > a front-buffer if you want to avoid artifacts). > > Real use-case: Wayland wl_shm buffers can be transparently converted Very nice, the Enlightenment developers have been asking for something like this for a while, it should help them out a lot as well. And thanks for the man pages and test code, if only all new apis came with that already... greg k-h