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Tue, 16 Feb 2021 10:57:10 -0500 (EST) Date: Tue, 16 Feb 2021 10:57:10 -0500 From: Vivek Goyal To: Stefan Hajnoczi Subject: Re: [PATCH 23/24] vhost-user-fs: Implement drop CAP_FSETID functionality Message-ID: <20210216155710.GB10195@redhat.com> References: <20210209190224.62827-1-dgilbert@redhat.com> <20210209190224.62827-24-dgilbert@redhat.com> <20210211143542.GT247031@stefanha-x1.localdomain> <20210211144031.GB5014@redhat.com> <20210215155711.GA95852@stefanha-x1.localdomain> MIME-Version: 1.0 In-Reply-To: <20210215155711.GA95852@stefanha-x1.localdomain> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=vgoyal@redhat.com 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=216.205.24.124; envelope-from=vgoyal@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no 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@redhat.com, marcandre.lureau@redhat.com, mst@redhat.com, "Dr. David Alan Gilbert \(git\)" , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Feb 15, 2021 at 03:57:11PM +0000, Stefan Hajnoczi wrote: > On Thu, Feb 11, 2021 at 09:40:31AM -0500, Vivek Goyal wrote: > > On Thu, Feb 11, 2021 at 02:35:42PM +0000, Stefan Hajnoczi wrote: > > > On Tue, Feb 09, 2021 at 07:02:23PM +0000, Dr. David Alan Gilbert (git) wrote: > > > > From: Vivek Goyal > > > > > > > > As part of slave_io message, slave can ask to do I/O on an fd. Additionally > > > > slave can ask for dropping CAP_FSETID (if master has it) before doing I/O. > > > > Implement functionality to drop CAP_FSETID and gain it back after the > > > > operation. > > > > > > > > This also creates a dependency on libcap-ng. > > > > > > Is this patch only for the case where QEMU is running as root? > > > > > > > Yes, it primarily is for the case where qemu is running as root, or > > somebody managed to launch it non-root but with still having capability > > CAP_FSETID. > > Running QEMU as root is not encouraged because the security model is > designed around the principle of least privilege (only give QEMU access > to resources that belong to the guest). > > What happens in the case where QEMU is not root? Does that mean QEMU > will drop suid/guid bits even if the FUSE client wanted them to be > preserved? QEMU will drop CAP_FSETID only if vhost-user slave asked for it. There is no notion of gaining CAP_FSETID. IOW, yes, if qemu is running unpriviliged and does not have CAP_FSETID, then we will end up clearing setuid bit on host. Not sure how that problem can be fixed. Vivek From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 16 Feb 2021 10:57:10 -0500 From: Vivek Goyal Message-ID: <20210216155710.GB10195@redhat.com> References: <20210209190224.62827-1-dgilbert@redhat.com> <20210209190224.62827-24-dgilbert@redhat.com> <20210211143542.GT247031@stefanha-x1.localdomain> <20210211144031.GB5014@redhat.com> <20210215155711.GA95852@stefanha-x1.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210215155711.GA95852@stefanha-x1.localdomain> Subject: Re: [Virtio-fs] [PATCH 23/24] vhost-user-fs: Implement drop CAP_FSETID functionality List-Id: Development discussions about virtio-fs List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: virtio-fs@redhat.com, marcandre.lureau@redhat.com, mst@redhat.com, qemu-devel@nongnu.org On Mon, Feb 15, 2021 at 03:57:11PM +0000, Stefan Hajnoczi wrote: > On Thu, Feb 11, 2021 at 09:40:31AM -0500, Vivek Goyal wrote: > > On Thu, Feb 11, 2021 at 02:35:42PM +0000, Stefan Hajnoczi wrote: > > > On Tue, Feb 09, 2021 at 07:02:23PM +0000, Dr. David Alan Gilbert (git) wrote: > > > > From: Vivek Goyal > > > > > > > > As part of slave_io message, slave can ask to do I/O on an fd. Additionally > > > > slave can ask for dropping CAP_FSETID (if master has it) before doing I/O. > > > > Implement functionality to drop CAP_FSETID and gain it back after the > > > > operation. > > > > > > > > This also creates a dependency on libcap-ng. > > > > > > Is this patch only for the case where QEMU is running as root? > > > > > > > Yes, it primarily is for the case where qemu is running as root, or > > somebody managed to launch it non-root but with still having capability > > CAP_FSETID. > > Running QEMU as root is not encouraged because the security model is > designed around the principle of least privilege (only give QEMU access > to resources that belong to the guest). > > What happens in the case where QEMU is not root? Does that mean QEMU > will drop suid/guid bits even if the FUSE client wanted them to be > preserved? QEMU will drop CAP_FSETID only if vhost-user slave asked for it. There is no notion of gaining CAP_FSETID. IOW, yes, if qemu is running unpriviliged and does not have CAP_FSETID, then we will end up clearing setuid bit on host. Not sure how that problem can be fixed. Vivek