Commit message: resolved: pin stream while calling callbacks for it

These callbacks might unref the stream, but we still have to access it,
let's hence ref it explicitly.

Maybe fixes: #10725
CVE: CVE-2022-2526
CWE: CWE-703
Vulnerability description: A use-after-free vulnerability was found in systemd. This issue occurs due to the on_stream_io() function and dns_stream_complete() function in 'resolved-dns-stream.c' not incrementing the reference counting for the DnsStream object. Therefore, other functions and callbacks called can dereference the DNSStream object, causing the use-after-free when the reference is still used later.

Project: systemd
File: resolved-dns-stream.c

static int dns_stream_complete(DnsStream *s, int error) {
        _cleanup_(dns_stream_unrefp) _unused_ DnsStream *ref = dns_stream_ref(s); /* Protect stream while we process it */

        assert(s);

#if ENABLE_DNS_OVER_TLS
        if (s->encrypted) {
                int r;

                r = dnstls_stream_shutdown(s, error);
                if (r != -EAGAIN)
                        dns_stream_stop(s);
        } else
#endif
                dns_stream_stop(s);

        if (s->complete)
                s->complete(s, error);
        else /* the default action if no completion function is set is to close the stream */
                dns_stream_unref(s);

        return 0;
}

Project: systemd
File: resolved-dns-stream.c

ssize_t dns_stream_writev(DnsStream *s, const struct iovec *iov, size_t iovcnt, int flags) {
        ssize_t m;

        assert(s);
        assert(iov);

#if ENABLE_DNS_OVER_TLS
        if (s->encrypted && !(flags & DNS_STREAM_WRITE_TLS_DATA)) {
                ssize_t ss;
                size_t i;

                m = 0;
                for (i = 0; i < iovcnt; i++) {
                        ss = dnstls_stream_write(s, iov[i].iov_base, iov[i].iov_len);
                        if (ss < 0)
                                return ss;

                        m += ss;
                        if (ss != (ssize_t) iov[i].iov_len)
                                continue;
                }
        } else
#endif
        if (s->tfo_salen > 0) {
                struct msghdr hdr = {
                        .msg_iov = (struct iovec*) iov,
                        .msg_iovlen = iovcnt,
                        .msg_name = &s->tfo_address.sa,
                        .msg_namelen = s->tfo_salen
                };

                m = sendmsg(s->fd, &hdr, MSG_FASTOPEN);
                if (m < 0) {
                        if (errno == EOPNOTSUPP) {
                                s->tfo_salen = 0;
                                if (connect(s->fd, &s->tfo_address.sa, s->tfo_salen) < 0)
                                        return -errno;

                                return -EAGAIN;
                        }
                        if (errno == EINPROGRESS)
                                return -EAGAIN;

                        return -errno;
                } else
                        s->tfo_salen = 0; /* connection is made */
        } else {
                m = writev(s->fd, iov, iovcnt);
                if (m < 0)
                        return -errno;
        }

        return m;
}

Project: systemd
File: resolved-dns-stream.c

DnsPacket *dns_stream_take_read_packet(DnsStream *s) {
        assert(s);

        if (!s->read_packet)
                return NULL;

        if (s->n_read < sizeof(s->read_size))
                return NULL;

        if (s->n_read < sizeof(s->read_size) + be16toh(s->read_size))
                return NULL;

        s->n_read = 0;
        return TAKE_PTR(s->read_packet);
}

Project: systemd
File: resolved-dns-stream.c

static int dns_stream_update_io(DnsStream *s) {
        int f = 0;

        assert(s);

        if (s->write_packet && s->n_written < sizeof(s->write_size) + s->write_packet->size)
                f |= EPOLLOUT;
        else if (!ordered_set_isempty(s->write_queue)) {
                dns_packet_unref(s->write_packet);
                s->write_packet = ordered_set_steal_first(s->write_queue);
                s->write_size = htobe16(s->write_packet->size);
                s->n_written = 0;
                f |= EPOLLOUT;
        }
        if (!s->read_packet || s->n_read < sizeof(s->read_size) + s->read_packet->size)
                f |= EPOLLIN;

#if ENABLE_DNS_OVER_TLS
        /* For handshake and clean closing purposes, TLS can override requested events */
        if (s->dnstls_events)
                f = s->dnstls_events;
#endif

        return sd_event_source_set_io_events(s->io_event_source, f);
}

Project: systemd
File: resolved-dns-stream.c

static int on_stream_timeout(sd_event_source *es, usec_t usec, void *userdata) {
        DnsStream *s = userdata;

        assert(s);

        return dns_stream_complete(s, ETIMEDOUT);
}

Project: systemd
File: resolved-dns-stream.c

static int dns_stream_identify(DnsStream *s) {
        union {
                struct cmsghdr header; /* For alignment */
                uint8_t buffer[CMSG_SPACE(MAXSIZE(struct in_pktinfo, struct in6_pktinfo))
                               + EXTRA_CMSG_SPACE /* kernel appears to require extra space */];
        } control;
        struct msghdr mh = {};
        struct cmsghdr *cmsg;
        socklen_t sl;
        int r;

        assert(s);

        if (s->identified)
                return 0;

        /* Query the local side */
        s->local_salen = sizeof(s->local);
        r = getsockname(s->fd, &s->local.sa, &s->local_salen);
        if (r < 0)
                return -errno;
        if (s->local.sa.sa_family == AF_INET6 && s->ifindex <= 0)
                s->ifindex = s->local.in6.sin6_scope_id;

        /* Query the remote side */
        s->peer_salen = sizeof(s->peer);
        r = getpeername(s->fd, &s->peer.sa, &s->peer_salen);
        if (r < 0)
                return -errno;
        if (s->peer.sa.sa_family == AF_INET6 && s->ifindex <= 0)
                s->ifindex = s->peer.in6.sin6_scope_id;

        /* Check consistency */
        assert(s->peer.sa.sa_family == s->local.sa.sa_family);
        assert(IN_SET(s->peer.sa.sa_family, AF_INET, AF_INET6));

        /* Query connection meta information */
        sl = sizeof(control);
        if (s->peer.sa.sa_family == AF_INET) {
                r = getsockopt(s->fd, IPPROTO_IP, IP_PKTOPTIONS, &control, &sl);
                if (r < 0)
                        return -errno;
        } else if (s->peer.sa.sa_family == AF_INET6) {

                r = getsockopt(s->fd, IPPROTO_IPV6, IPV6_2292PKTOPTIONS, &control, &sl);
                if (r < 0)
                        return -errno;
        } else
                return -EAFNOSUPPORT;

        mh.msg_control = &control;
        mh.msg_controllen = sl;

        CMSG_FOREACH(cmsg, &mh) {

                if (cmsg->cmsg_level == IPPROTO_IPV6) {
                        assert(s->peer.sa.sa_family == AF_INET6);

                        switch (cmsg->cmsg_type) {

                        case IPV6_PKTINFO: {
                                struct in6_pktinfo *i = (struct in6_pktinfo*) CMSG_DATA(cmsg);

                                if (s->ifindex <= 0)
                                        s->ifindex = i->ipi6_ifindex;
                                break;
                        }

                        case IPV6_HOPLIMIT:
                                s->ttl = *(int *) CMSG_DATA(cmsg);
                                break;
                        }

                } else if (cmsg->cmsg_level == IPPROTO_IP) {
                        assert(s->peer.sa.sa_family == AF_INET);

                        switch (cmsg->cmsg_type) {

                        case IP_PKTINFO: {
                                struct in_pktinfo *i = (struct in_pktinfo*) CMSG_DATA(cmsg);

                                if (s->ifindex <= 0)
                                        s->ifindex = i->ipi_ifindex;
                                break;
                        }

                        case IP_TTL:
                                s->ttl = *(int *) CMSG_DATA(cmsg);
                                break;
                        }
                }
        }

        /* The Linux kernel sets the interface index to the loopback
         * device if the connection came from the local host since it
         * avoids the routing table in such a case. Let's unset the
         * interface index in such a case. */
        if (s->ifindex == LOOPBACK_IFINDEX)
                s->ifindex = 0;

        /* If we don't know the interface index still, we look for the
         * first local interface with a matching address. Yuck! */
        if (s->ifindex <= 0)
                s->ifindex = manager_find_ifindex(s->manager, s->local.sa.sa_family, s->local.sa.sa_family == AF_INET ? (union in_addr_union*) &s->local.in.sin_addr : (union in_addr_union*)  &s->local.in6.sin6_addr);

        if (s->protocol == DNS_PROTOCOL_LLMNR && s->ifindex > 0) {
                uint32_t ifindex = htobe32(s->ifindex);

                /* Make sure all packets for this connection are sent on the same interface */
                if (s->local.sa.sa_family == AF_INET) {
                        r = setsockopt(s->fd, IPPROTO_IP, IP_UNICAST_IF, &ifindex, sizeof(ifindex));
                        if (r < 0)
                                log_debug_errno(errno, "Failed to invoke IP_UNICAST_IF: %m");
                } else if (s->local.sa.sa_family == AF_INET6) {
                        r = setsockopt(s->fd, IPPROTO_IPV6, IPV6_UNICAST_IF, &ifindex, sizeof(ifindex));
                        if (r < 0)
                                log_debug_errno(errno, "Failed to invoke IPV6_UNICAST_IF: %m");
                }
        }

        s->identified = true;

        return 0;
}

Project: systemd
File: resolved-dns-stream.c

static ssize_t dns_stream_read(DnsStream *s, void *buf, size_t count) {
        ssize_t ss;

#if ENABLE_DNS_OVER_TLS
        if (s->encrypted)
                ss = dnstls_stream_read(s, buf, count);
        else
#endif
        {
                ss = read(s->fd, buf, count);
                if (ss < 0)
                        return -errno;
        }

        return ss;
}

Project: systemd
File: resolved-dns-stream.c

static DnsStream *dns_stream_free(DnsStream *s) {
        DnsPacket *p;
        Iterator i;

        assert(s);

        dns_stream_stop(s);

        if (s->server && s->server->stream == s)
                s->server->stream = NULL;

        if (s->manager) {
                LIST_REMOVE(streams, s->manager->dns_streams, s);
                s->manager->n_dns_streams--;
        }

#if ENABLE_DNS_OVER_TLS
        if (s->encrypted)
                dnstls_stream_free(s);
#endif

        ORDERED_SET_FOREACH(p, s->write_queue, i)
                dns_packet_unref(ordered_set_remove(s->write_queue, p));

        dns_packet_unref(s->write_packet);
        dns_packet_unref(s->read_packet);
        dns_server_unref(s->server);

        ordered_set_free(s->write_queue);

        return mfree(s);
}

Project: systemd
File: resolved-dns-stream.c

int dns_stream_new(
                Manager *m,
                DnsStream **ret,
                DnsProtocol protocol,
                int fd,
                const union sockaddr_union *tfo_address) {

        _cleanup_(dns_stream_unrefp) DnsStream *s = NULL;
        int r;

        assert(m);
        assert(ret);
        assert(fd >= 0);

        if (m->n_dns_streams > DNS_STREAMS_MAX)
                return -EBUSY;

        s = new(DnsStream, 1);
        if (!s)
                return -ENOMEM;

        *s = (DnsStream) {
                .n_ref = 1,
                .fd = -1,
                .protocol = protocol,
        };

        r = ordered_set_ensure_allocated(&s->write_queue, &dns_packet_hash_ops);
        if (r < 0)
                return r;

        r = sd_event_add_io(m->event, &s->io_event_source, fd, EPOLLIN, on_stream_io, s);
        if (r < 0)
                return r;

        (void) sd_event_source_set_description(s->io_event_source, "dns-stream-io");

        r = sd_event_add_time(
                        m->event,
                        &s->timeout_event_source,
                        clock_boottime_or_monotonic(),
                        now(clock_boottime_or_monotonic()) + DNS_STREAM_TIMEOUT_USEC, 0,
                        on_stream_timeout, s);
        if (r < 0)
                return r;

        (void) sd_event_source_set_description(s->timeout_event_source, "dns-stream-timeout");

        LIST_PREPEND(streams, m->dns_streams, s);
        m->n_dns_streams++;
        s->manager = m;

        s->fd = fd;

        if (tfo_address) {
                s->tfo_address = *tfo_address;
                s->tfo_salen = tfo_address->sa.sa_family == AF_INET6 ? sizeof(tfo_address->in6) : sizeof(tfo_address->in);
        }

        *ret = TAKE_PTR(s);

        return 0;
}

Project: systemd
File: resolved-dns-stream.c

int dns_stream_write_packet(DnsStream *s, DnsPacket *p) {
        int r;

        assert(s);
        assert(p);

        r = ordered_set_put(s->write_queue, p);
        if (r < 0)
                return r;

        dns_packet_ref(p);

        return dns_stream_update_io(s);
}

Project: systemd
File: resolved-dns-stream.c

static void dns_stream_stop(DnsStream *s) {
        assert(s);

        s->io_event_source = sd_event_source_unref(s->io_event_source);
        s->timeout_event_source = sd_event_source_unref(s->timeout_event_source);
        s->fd = safe_close(s->fd);
}

Project: systemd
File: resolved-dns-stream.c

static int on_stream_io(sd_event_source *es, int fd, uint32_t revents, void *userdata) {
        _cleanup_(dns_stream_unrefp) DnsStream *s = dns_stream_ref(userdata); /* Protect stream while we process it */
        int r;

        assert(s);

#if ENABLE_DNS_OVER_TLS
        if (s->encrypted) {
                r = dnstls_stream_on_io(s, revents);
                if (r == DNSTLS_STREAM_CLOSED)
                        return 0;
                if (r == -EAGAIN)
                        return dns_stream_update_io(s);
                if (r < 0)
                        return dns_stream_complete(s, -r);

                r = dns_stream_update_io(s);
                if (r < 0)
                        return r;
        }
#endif

        /* only identify after connecting */
        if (s->tfo_salen == 0) {
                r = dns_stream_identify(s);
                if (r < 0)
                        return dns_stream_complete(s, -r);
        }

        if ((revents & EPOLLOUT) &&
            s->write_packet &&
            s->n_written < sizeof(s->write_size) + s->write_packet->size) {

                struct iovec iov[2];
                ssize_t ss;

                iov[0] = IOVEC_MAKE(&s->write_size, sizeof(s->write_size));
                iov[1] = IOVEC_MAKE(DNS_PACKET_DATA(s->write_packet), s->write_packet->size);

                IOVEC_INCREMENT(iov, 2, s->n_written);

                ss = dns_stream_writev(s, iov, 2, 0);
                if (ss < 0) {
                        if (!IN_SET(-ss, EINTR, EAGAIN))
                                return dns_stream_complete(s, -ss);
                } else
                        s->n_written += ss;

                /* Are we done? If so, disable the event source for EPOLLOUT */
                if (s->n_written >= sizeof(s->write_size) + s->write_packet->size) {
                        r = dns_stream_update_io(s);
                        if (r < 0)
                                return dns_stream_complete(s, -r);
                }
        }

        if ((revents & (EPOLLIN|EPOLLHUP|EPOLLRDHUP)) &&
            (!s->read_packet ||
             s->n_read < sizeof(s->read_size) + s->read_packet->size)) {

                if (s->n_read < sizeof(s->read_size)) {
                        ssize_t ss;

                        ss = dns_stream_read(s, (uint8_t*) &s->read_size + s->n_read, sizeof(s->read_size) - s->n_read);
                        if (ss < 0) {
                                if (!IN_SET(-ss, EINTR, EAGAIN))
                                        return dns_stream_complete(s, -ss);
                        } else if (ss == 0)
                                return dns_stream_complete(s, ECONNRESET);
                        else
                                s->n_read += ss;
                }

                if (s->n_read >= sizeof(s->read_size)) {

                        if (be16toh(s->read_size) < DNS_PACKET_HEADER_SIZE)
                                return dns_stream_complete(s, EBADMSG);

                        if (s->n_read < sizeof(s->read_size) + be16toh(s->read_size)) {
                                ssize_t ss;

                                if (!s->read_packet) {
                                        r = dns_packet_new(&s->read_packet, s->protocol, be16toh(s->read_size), DNS_PACKET_SIZE_MAX);
                                        if (r < 0)
                                                return dns_stream_complete(s, -r);

                                        s->read_packet->size = be16toh(s->read_size);
                                        s->read_packet->ipproto = IPPROTO_TCP;
                                        s->read_packet->family = s->peer.sa.sa_family;
                                        s->read_packet->ttl = s->ttl;
                                        s->read_packet->ifindex = s->ifindex;

                                        if (s->read_packet->family == AF_INET) {
                                                s->read_packet->sender.in = s->peer.in.sin_addr;
                                                s->read_packet->sender_port = be16toh(s->peer.in.sin_port);
                                                s->read_packet->destination.in = s->local.in.sin_addr;
                                                s->read_packet->destination_port = be16toh(s->local.in.sin_port);
                                        } else {
                                                assert(s->read_packet->family == AF_INET6);
                                                s->read_packet->sender.in6 = s->peer.in6.sin6_addr;
                                                s->read_packet->sender_port = be16toh(s->peer.in6.sin6_port);
                                                s->read_packet->destination.in6 = s->local.in6.sin6_addr;
                                                s->read_packet->destination_port = be16toh(s->local.in6.sin6_port);

                                                if (s->read_packet->ifindex == 0)
                                                        s->read_packet->ifindex = s->peer.in6.sin6_scope_id;
                                                if (s->read_packet->ifindex == 0)
                                                        s->read_packet->ifindex = s->local.in6.sin6_scope_id;
                                        }
                                }

                                ss = dns_stream_read(s,
                                          (uint8_t*) DNS_PACKET_DATA(s->read_packet) + s->n_read - sizeof(s->read_size),
                                          sizeof(s->read_size) + be16toh(s->read_size) - s->n_read);
                                if (ss < 0) {
                                        if (!IN_SET(-ss, EINTR, EAGAIN))
                                                return dns_stream_complete(s, -ss);
                                } else if (ss == 0)
                                        return dns_stream_complete(s, ECONNRESET);
                                else
                                        s->n_read += ss;
                        }

                        /* Are we done? If so, disable the event source for EPOLLIN */
                        if (s->n_read >= sizeof(s->read_size) + be16toh(s->read_size)) {
                                /* If there's a packet handler
                                 * installed, call that. Note that
                                 * this is optional... */
                                if (s->on_packet) {
                                        r = s->on_packet(s);
                                        if (r < 0)
                                                return r;
                                }

                                r = dns_stream_update_io(s);
                                if (r < 0)
                                        return dns_stream_complete(s, -r);
                        }
                }
        }

        if ((s->write_packet && s->n_written >= sizeof(s->write_size) + s->write_packet->size) &&
            (s->read_packet && s->n_read >= sizeof(s->read_size) + s->read_packet->size))
                return dns_stream_complete(s, 0);

        return 0;
}