From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH 04/24] VFS: Add LSM hooks for filesystem context [ver #7] To: David Howells Cc: Paul Moore , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, viro@zeniv.linux.org.uk, selinux@tycho.nsa.gov, linux-fsdevel@vger.kernel.org, linux-afs@lists.infradead.org References: <152414466005.23902.12967974041384198114.stgit@warthog.procyon.org.uk> <152414469006.23902.8132059438921850399.stgit@warthog.procyon.org.uk> <3232.1524238511@warthog.procyon.org.uk> <703.1524583367@warthog.procyon.org.uk> From: Stephen Smalley Message-ID: <1bb08eac-517a-a07e-5e64-5771cc0c0afc@tycho.nsa.gov> Date: Wed, 25 Apr 2018 10:07:15 -0400 MIME-Version: 1.0 In-Reply-To: <703.1524583367@warthog.procyon.org.uk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: On 04/24/2018 11:22 AM, David Howells wrote: > Stephen Smalley wrote: > >> Neither fsopen() nor fscontext_fs_write() appear to perform any kind of >> up-front permission checking (DAC or MAC), although some security hooks may >> be ultimately called to allocate structures, parse security options, etc. >> Is there a reason not apply a may_mount() or similar check up front? > > may_mount() is called by fsmount() at the moment. It may make sense to move > this earlier to fsopen(). Note that there's also going to be something that > looks like: > > fd = fspick("/mnt"); > fsmount(fd, "/a", MNT_NOEXEC); // ie. bind mount > > or: > > fd = fspick("/mnt"); > write(fd, "o intr"); > write(fd, "x reconfigure"); // ie. something like remount > close(fd); > > I guess we'd want to call may_mount() in fspick() too. But there's also the > possibility of using this to create a query interfact too: > > fd = fspick("/mnt"); > write(fd, "q intr"); > read(fd, value_buffer); My concern was that fsopen()/fscontext_fs_write() may expose attack surface (e.g. mount option parsing code) that might not be normally accessible to unprivileged userspace (i.e. gated by may_mount() and security_sb_mount()) prior to your changes.