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Fri, 19 Jun 2020 11:12:47 +0000 (UTC) Date: Fri, 19 Jun 2020 12:12:44 +0100 From: "Dr. David Alan Gilbert" To: Chirantan Ekbote Subject: Re: [Virtio-fs] [PATCH 0/2] virtiofsd: drop Linux capabilities(7) Message-ID: <20200619111244.GE2690@work-vm> References: <20200416164907.244868-1-stefanha@redhat.com> <20200618190816.GD3814@redhat.com> <20200618191655.GI2769@work-vm> <20200618192717.GE3814@redhat.com> <20200619083953.GB2690@work-vm> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.14.0 (2020-05-02) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.61; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/19 02:45:39 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: virtio-fs-list , qemu-devel@nongnu.org, Vivek Goyal , Miklos Szeredi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Chirantan Ekbote (chirantan@chromium.org) wrote: > On Fri, Jun 19, 2020 at 5:40 PM Dr. David Alan Gilbert > wrote: > > > > * Chirantan Ekbote (chirantan@chromium.org) wrote: > > > > > We ended up working around it by prefixing "user.virtiofs." to the > > > xattr name[2], which has its own problems but there was pretty much no > > > chance that we would be able to give the fs device CAP_SYS_ADMIN in > > > the init namespace. > > > > > > What problems did you hit with that? We should standardise the renaming > > so we make an on-disc format that's compatible. > > > > I guess what I meant by problems is that it made what was previously a > simple and straightforward implementation into something more complex > and added some limitations. Yeh. > For example, we now need to parse the > result of the listxattr system call and strip out the prefix from any > name in the list. It also means that we cannot allow the guest to > directly set or remove any "user.virtiofs." xattr as this would allow > an unprivileged process in the vm to modify an xattr that it wouldn't > otherwise be allowed to modify. On top of being a somewhat arbitrary > restriction this also means that you can't have stacked virtiofs > instances as the lower instance would reject attempts by the upper one > to set those xattrs. These limitations aren't really a problem for us > but I can see how they might be a problem for others. Isn't this a classic escaping problem? Would it work if you prepended 'user.virtiofs.' onto any xattr that started with 'trusted' or 'user.virtiofs.' ? > The change was also merged just yesterday so there may be other > problems with it that haven't surfaced yet. > > I didn't mention it before because I figured this was something that > we brought upon ourselves as chrome os is a bit extreme about > sandboxing. I think we're trying to be as extreme in virtiofsd, but it is causing us similar problems. > If we can come up with a standardized way to handle this > I think we'll gladly switch the chrome os implementation to use it. Great! Dave > > Chirantan > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK