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Fri, 1 May 2020 17:47:27 +0000 (UTC) Received: from work-vm (ovpn-112-191.ams2.redhat.com [10.36.112.191]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A4DBA10013BD; Fri, 1 May 2020 17:47:23 +0000 (UTC) Date: Fri, 1 May 2020 18:47:21 +0100 From: "Dr. David Alan Gilbert" To: Miklos Szeredi Subject: Re: [PATCH] virtiofsd: jail lo->proc_self_fd Message-ID: <20200501174721.GB38251@work-vm> References: <20200429124733.22488-1-mszeredi@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200429124733.22488-1-mszeredi@redhat.com> User-Agent: Mutt/1.13.4 (2020-02-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable 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 = 2020/05/01 12:40:15 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 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, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Miklos Szeredi (mszeredi@redhat.com) wrote: > While it's not possible to escape the proc filesystem through > lo->proc_self_fd, it is possible to escape to the root of the proc > filesystem itself through "../..". >=20 > Use a temporary mount for opening lo->proc_self_fd, that has it's root at > /proc/self/fd/, preventing access to the ancestor directories. >=20 > Signed-off-by: Miklos Szeredi Queued > --- > tools/virtiofsd/passthrough_ll.c | 27 +++++++++++++++++++++++++-- > 1 file changed, 25 insertions(+), 2 deletions(-) >=20 > diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrou= gh_ll.c > index 4c35c95b256c..bc9c44c760f4 100644 > --- a/tools/virtiofsd/passthrough_ll.c > +++ b/tools/virtiofsd/passthrough_ll.c > @@ -2536,6 +2536,8 @@ static void print_capabilities(void) > static void setup_namespaces(struct lo_data *lo, struct fuse_session *se= ) > { > pid_t child; > + char template[] =3D "virtiofsd-XXXXXX"; > + char *tmpdir; > =20 > /* > * Create a new pid namespace for *child* processes. We'll have to > @@ -2597,12 +2599,33 @@ static void setup_namespaces(struct lo_data *lo, = struct fuse_session *se) > exit(1); > } > =20 > + tmpdir =3D mkdtemp(template); > + if (!tmpdir) { > + fuse_log(FUSE_LOG_ERR, "tmpdir(%s): %m\n", template); > + exit(1); > + } > + > + if (mount("/proc/self/fd", tmpdir, NULL, MS_BIND, NULL) < 0) { > + fuse_log(FUSE_LOG_ERR, "mount(/proc/self/fd, %s, MS_BIND): %m\n"= , > + tmpdir); > + exit(1); > + } > + > /* Now we can get our /proc/self/fd directory file descriptor */ > - lo->proc_self_fd =3D open("/proc/self/fd", O_PATH); > + lo->proc_self_fd =3D open(tmpdir, O_PATH); > if (lo->proc_self_fd =3D=3D -1) { > - fuse_log(FUSE_LOG_ERR, "open(/proc/self/fd, O_PATH): %m\n"); > + fuse_log(FUSE_LOG_ERR, "open(%s, O_PATH): %m\n", tmpdir); > exit(1); > } > + > + if (umount2(tmpdir, MNT_DETACH) < 0) { > + fuse_log(FUSE_LOG_ERR, "umount2(%s, MNT_DETACH): %m\n", tmpdir); > + exit(1); > + } > + > + if (rmdir(tmpdir) < 0) { > + fuse_log(FUSE_LOG_ERR, "rmdir(%s): %m\n", tmpdir); > + } > } > =20 > /* > --=20 > 2.21.1 >=20 >=20 -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK