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Mon, 11 Nov 2019 16:41:06 +0000 (UTC) Date: Mon, 11 Nov 2019 16:41:05 +0000 From: Stefan Hajnoczi To: Jagannathan Raman Subject: Re: [RFC v4 PATCH 07/49] multi-process: define mpqemu-link object Message-ID: <20191111164105.GK402228@stefanha-x1.localdomain> References: MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="Rex5+51txc1ort/q" Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 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: elena.ufimtseva@oracle.com, fam@euphon.net, thuth@redhat.com, john.g.johnson@oracle.com, ehabkost@redhat.com, konrad.wilk@oracle.com, quintela@redhat.com, berrange@redhat.com, mst@redhat.com, qemu-devel@nongnu.org, armbru@redhat.com, ross.lagerwall@citrix.com, kanth.ghatraju@oracle.com, kraxel@redhat.com, kwolf@redhat.com, pbonzini@redhat.com, liran.alon@oracle.com, marcandre.lureau@gmail.com, mreitz@redhat.com, dgilbert@redhat.com, rth@twiddle.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --Rex5+51txc1ort/q Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Thu, Oct 24, 2019 at 05:08:48AM -0400, Jagannathan Raman wrote: > +int mpqemu_msg_recv(MPQemuLinkState *s, MPQemuMsg *msg, MPQemuChannel *chan) > +{ > + int rc; > + uint8_t *data; > + union { > + char control[CMSG_SPACE(REMOTE_MAX_FDS * sizeof(int))]; > + struct cmsghdr align; > + } u; > + struct msghdr hdr; > + struct cmsghdr *chdr; > + size_t fdsize; > + int sock = chan->sock; > + QemuMutex *lock = &chan->recv_lock; > + > + struct iovec iov = { > + .iov_base = (char *) msg, > + .iov_len = MPQEMU_MSG_HDR_SIZE, > + }; > + > + memset(&hdr, 0, sizeof(hdr)); > + memset(&u, 0, sizeof(u)); > + > + hdr.msg_iov = &iov; > + hdr.msg_iovlen = 1; > + hdr.msg_control = &u; > + hdr.msg_controllen = sizeof(u); > + > + qemu_mutex_lock(lock); > + > + do { > + rc = recvmsg(sock, &hdr, 0); > + } while (rc < 0 && (errno == EINTR || errno == EAGAIN)); > + > + if (rc < 0) { > + qemu_log_mask(LOG_REMOTE_DEBUG, "%s - recvmsg rc is %d, errno is %d," > + " sock %d\n", __func__, rc, errno, sock); > + qemu_mutex_unlock(lock); > + return rc; > + } > + > + msg->num_fds = 0; > + for (chdr = CMSG_FIRSTHDR(&hdr); chdr != NULL; > + chdr = CMSG_NXTHDR(&hdr, chdr)) { > + if ((chdr->cmsg_level == SOL_SOCKET) && > + (chdr->cmsg_type == SCM_RIGHTS)) { > + fdsize = chdr->cmsg_len - CMSG_LEN(0); > + msg->num_fds = fdsize / sizeof(int); > + if (msg->num_fds > REMOTE_MAX_FDS) { > + /* > + * TODO: Security issue detected. Sender never sends more > + * than REMOTE_MAX_FDS. This condition should be signaled to > + * the admin > + */ > + qemu_log_mask(LOG_REMOTE_DEBUG, "%s: Max FDs exceeded\n", __func__); > + return -ERANGE; > + } > + > + memcpy(msg->fds, CMSG_DATA(chdr), fdsize); > + break; > + } > + } > + > + if (msg->size && msg->bytestream) { > + msg->data2 = calloc(1, msg->size); > + data = msg->data2; > + } else { > + data = (uint8_t *)&msg->data1; > + } > + > + if (msg->size) { > + do { > + rc = read(sock, data, msg->size); > + } while (rc < 0 && (errno == EINTR || errno == EAGAIN)); > + } > + > + qemu_mutex_unlock(lock); > + > + return rc; > +} This code is still insecure. Until the communication between processes is made secure this series does not meet its goal of providing process isolation. 1. An attacker can overflow msg->data1 easily by setting msg->size but not msg->bytestream. 2. An attacker can allocate data2, all mpqemu_msg_recv() callers need to free it to prevent memory leaks. 3. mpqemu_msg_recv() callers generally do not validate untrusted msg fields. All the code needs to be audited. Stefan --Rex5+51txc1ort/q Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAl3JjyEACgkQnKSrs4Gr c8g+qgf/dMOSi4N9PQLrsAN0C1/9EvLCJ+Fy21aS96Q7t0cyavoSSrnOEsWnB5Ey rCt7XAHIZfE49RrFsZYI3taDMOy+cNDjQzT2sujgVvAKlUuSnsqbPkE/YHFHxOzc xRIo3Y1eZx6n7ediHGDmtOgboxrs6DOWHyus+VbzIDjyAmNUqkk2LGQTtjZa+v/k JC5LFTeitesPz2I6Y7IWA7DpX0uQTG5Th2exNz2UvpunvE2Rkps53FWlFbkeiKe+ RnAq/ycVDpBE7SPiNxr9EuhZnMCF6cb0D9LaRO1bm7cU30lCT+VEkFUdH5SxDZT1 JD2Jl2bC5u+44hZdRKAyDulSfrYTPg== =RKF2 -----END PGP SIGNATURE----- --Rex5+51txc1ort/q--