Commit message: journald: set a limit on the number of fields (1k)

We allocate a iovec entry for each field, so with many short entries,
our memory usage and processing time can be large, even with a relatively
small message size. Let's refuse overly long entries.

CVE-2018-16865
https://bugzilla.redhat.com/show_bug.cgi?id=1653861

What from I can see, the problem is not from an alloca, despite what the CVE
description says, but from the attack multiplication that comes from creating
many very small iovecs: (void* + size_t) for each three bytes of input message.
CVE: CVE-2018-16865
CWE: CWE-770
Vulnerability description: An allocation of memory without limits, that could result in the stack clashing with another memory region, was discovered in systemd-journald when many entries are sent to the journal socket. A local attacker, or a remote one if systemd-journal-remote is used, may use this flaw to crash systemd-journald or execute code with journald privileges. Versions through v240 are vulnerable.

Project: systemd
File: journald-native.c

static int server_process_entry(
                Server *s,
                const void *buffer, size_t *remaining,
                ClientContext *context,
                const struct ucred *ucred,
                const struct timeval *tv,
                const char *label, size_t label_len) {

        /* Process a single entry from a native message. Returns 0 if nothing special happened and the message
         * processing should continue, and a negative or positive value otherwise.
         *
         * Note that *remaining is altered on both success and failure. */

        size_t n = 0, j, tn = (size_t) -1, m = 0, entry_size = 0;
        char *identifier = NULL, *message = NULL;
        struct iovec *iovec = NULL;
        int priority = LOG_INFO;
        pid_t object_pid = 0;
        const char *p;
        int r = 0;

        p = buffer;

        while (*remaining > 0) {
                const char *e, *q;

                e = memchr(p, '\n', *remaining);

                if (!e) {
                        /* Trailing noise, let's ignore it, and flush what we collected */
                        log_debug("Received message with trailing noise, ignoring.");
                        r = 1; /* finish processing of the message */
                        break;
                }

                if (e == p) {
                        /* Entry separator */
                        *remaining -= 1;
                        break;
                }

                if (IN_SET(*p, '.', '#')) {
                        /* Ignore control commands for now, and
                         * comments too. */
                        *remaining -= (e - p) + 1;
                        p = e + 1;
                        continue;
                }

                /* A property follows */
                if (n > ENTRY_FIELD_COUNT_MAX) {
                        log_debug("Received an entry that has more than " STRINGIFY(ENTRY_FIELD_COUNT_MAX) " fields, ignoring entry.");
                        r = 1;
                        goto finish;
                }

                /* n existing properties, 1 new, +1 for _TRANSPORT */
                if (!GREEDY_REALLOC(iovec, m,
                                    n + 2 +
                                    N_IOVEC_META_FIELDS + N_IOVEC_OBJECT_FIELDS +
                                    client_context_extra_fields_n_iovec(context))) {
                        r = log_oom();
                        break;
                }

                q = memchr(p, '=', e - p);
                if (q) {
                        if (journal_field_valid(p, q - p, false)) {
                                size_t l;

                                l = e - p;

                                /* If the field name starts with an underscore, skip the variable, since that indicates
                                 * a trusted field */
                                iovec[n++] = IOVEC_MAKE((char*) p, l);
                                entry_size += l;

                                server_process_entry_meta(p, l, ucred,
                                                          &priority,
                                                          &identifier,
                                                          &message,
                                                          &object_pid);
                        }

                        *remaining -= (e - p) + 1;
                        p = e + 1;
                        continue;
                } else {
                        uint64_t l;
                        char *k;

                        if (*remaining < e - p + 1 + sizeof(uint64_t) + 1) {
                                log_debug("Failed to parse message, ignoring.");
                                break;
                        }

                        l = unaligned_read_le64(e + 1);

                        if (l > DATA_SIZE_MAX) {
                                log_debug("Received binary data block of %"PRIu64" bytes is too large, ignoring.", l);
                                break;
                        }

                        if ((uint64_t) *remaining < e - p + 1 + sizeof(uint64_t) + l + 1 ||
                            e[1+sizeof(uint64_t)+l] != '\n') {
                                log_debug("Failed to parse message, ignoring.");
                                break;
                        }

                        k = malloc((e - p) + 1 + l);
                        if (!k) {
                                log_oom();
                                break;
                        }

                        memcpy(k, p, e - p);
                        k[e - p] = '=';
                        memcpy(k + (e - p) + 1, e + 1 + sizeof(uint64_t), l);

                        if (journal_field_valid(p, e - p, false)) {
                                iovec[n] = IOVEC_MAKE(k, (e - p) + 1 + l);
                                entry_size += iovec[n].iov_len;
                                n++;

                                server_process_entry_meta(k, (e - p) + 1 + l, ucred,
                                                          &priority,
                                                          &identifier,
                                                          &message,
                                                          &object_pid);
                        } else
                                free(k);

                        *remaining -= (e - p) + 1 + sizeof(uint64_t) + l + 1;
                        p = e + 1 + sizeof(uint64_t) + l + 1;
                }
        }

        if (n <= 0) {
                r = 1;
                goto finish;
        }

        if (!client_context_test_priority(context, priority)) {
                r = 0;
                goto finish;
        }

        tn = n++;
        iovec[tn] = IOVEC_MAKE_STRING("_TRANSPORT=journal");
        entry_size += STRLEN("_TRANSPORT=journal");

        if (entry_size + n + 1 > ENTRY_SIZE_MAX) { /* data + separators + trailer */
                log_debug("Entry is too big with %zu properties and %zu bytes, ignoring.", n, entry_size);
                goto finish;
        }

        if (message) {
                if (s->forward_to_syslog)
                        server_forward_syslog(s, syslog_fixup_facility(priority), identifier, message, ucred, tv);

                if (s->forward_to_kmsg)
                        server_forward_kmsg(s, priority, identifier, message, ucred);

                if (s->forward_to_console)
                        server_forward_console(s, priority, identifier, message, ucred);

                if (s->forward_to_wall)
                        server_forward_wall(s, priority, identifier, message, ucred);
        }

        server_dispatch_message(s, iovec, n, m, context, tv, priority, object_pid);

finish:
        for (j = 0; j < n; j++)  {
                if (j == tn)
                        continue;

                if (iovec[j].iov_base < buffer ||
                    (const char*) iovec[j].iov_base >= p + *remaining)
                        free(iovec[j].iov_base);
        }

        free(iovec);
        free(identifier);
        free(message);

        return r;
}

Project: systemd
File: journald-native.c

static bool allow_object_pid(const struct ucred *ucred) {
        return ucred && ucred->uid == 0;
}

Project: systemd
File: journald-native.c

void server_process_native_file(
                Server *s,
                int fd,
                const struct ucred *ucred,
                const struct timeval *tv,
                const char *label, size_t label_len) {

        struct stat st;
        bool sealed;
        int r;

        /* Data is in the passed fd, since it didn't fit in a
         * datagram. */

        assert(s);
        assert(fd >= 0);

        /* If it's a memfd, check if it is sealed. If so, we can just
         * use map it and use it, and do not need to copy the data
         * out. */
        sealed = memfd_get_sealed(fd) > 0;

        if (!sealed && (!ucred || ucred->uid != 0)) {
                _cleanup_free_ char *k = NULL;
                const char *e;

                /* If this is not a sealed memfd, and the peer is unknown or
                 * unprivileged, then verify the path. */

                r = fd_get_path(fd, &k);
                if (r < 0) {
                        log_error_errno(r, "readlink(/proc/self/fd/%i) failed: %m", fd);
                        return;
                }

                e = PATH_STARTSWITH_SET(k, "/dev/shm/", "/tmp/", "/var/tmp/");
                if (!e) {
                        log_error("Received file outside of allowed directories. Refusing.");
                        return;
                }

                if (!filename_is_valid(e)) {
                        log_error("Received file in subdirectory of allowed directories. Refusing.");
                        return;
                }
        }

        if (fstat(fd, &st) < 0) {
                log_error_errno(errno, "Failed to stat passed file, ignoring: %m");
                return;
        }

        if (!S_ISREG(st.st_mode)) {
                log_error("File passed is not regular. Ignoring.");
                return;
        }

        if (st.st_size <= 0)
                return;

        if (st.st_size > ENTRY_SIZE_MAX) {
                log_error("File passed too large. Ignoring.");
                return;
        }

        if (sealed) {
                void *p;
                size_t ps;

                /* The file is sealed, we can just map it and use it. */

                ps = PAGE_ALIGN(st.st_size);
                p = mmap(NULL, ps, PROT_READ, MAP_PRIVATE, fd, 0);
                if (p == MAP_FAILED) {
                        log_error_errno(errno, "Failed to map memfd, ignoring: %m");
                        return;
                }

                server_process_native_message(s, p, st.st_size, ucred, tv, label, label_len);
                assert_se(munmap(p, ps) >= 0);
        } else {
                _cleanup_free_ void *p = NULL;
                struct statvfs vfs;
                ssize_t n;

                if (fstatvfs(fd, &vfs) < 0) {
                        log_error_errno(errno, "Failed to stat file system of passed file, ignoring: %m");
                        return;
                }

                /* Refuse operating on file systems that have
                 * mandatory locking enabled, see:
                 *
                 * https://github.com/systemd/systemd/issues/1822
                 */
                if (vfs.f_flag & ST_MANDLOCK) {
                        log_error("Received file descriptor from file system with mandatory locking enabled, refusing.");
                        return;
                }

                /* Make the fd non-blocking. On regular files this has
                 * the effect of bypassing mandatory locking. Of
                 * course, this should normally not be necessary given
                 * the check above, but let's better be safe than
                 * sorry, after all NFS is pretty confusing regarding
                 * file system flags, and we better don't trust it,
                 * and so is SMB. */
                r = fd_nonblock(fd, true);
                if (r < 0) {
                        log_error_errno(r, "Failed to make fd non-blocking, ignoring: %m");
                        return;
                }

                /* The file is not sealed, we can't map the file here, since
                 * clients might then truncate it and trigger a SIGBUS for
                 * us. So let's stupidly read it */

                p = malloc(st.st_size);
                if (!p) {
                        log_oom();
                        return;
                }

                n = pread(fd, p, st.st_size, 0);
                if (n < 0)
                        log_error_errno(errno, "Failed to read file, ignoring: %m");
                else if (n > 0)
                        server_process_native_message(s, p, n, ucred, tv, label, label_len);
        }
}

Project: systemd
File: journald-native.c

int server_open_native_socket(Server *s) {

        static const union sockaddr_union sa = {
                .un.sun_family = AF_UNIX,
                .un.sun_path = "/run/systemd/journal/socket",
        };
        int r;

        assert(s);

        if (s->native_fd < 0) {
                s->native_fd = socket(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
                if (s->native_fd < 0)
                        return log_error_errno(errno, "socket() failed: %m");

                (void) sockaddr_un_unlink(&sa.un);

                r = bind(s->native_fd, &sa.sa, SOCKADDR_UN_LEN(sa.un));
                if (r < 0)
                        return log_error_errno(errno, "bind(%s) failed: %m", sa.un.sun_path);

                (void) chmod(sa.un.sun_path, 0666);
        } else
                (void) fd_nonblock(s->native_fd, true);

        r = setsockopt_int(s->native_fd, SOL_SOCKET, SO_PASSCRED, true);
        if (r < 0)
                return log_error_errno(r, "SO_PASSCRED failed: %m");

#if HAVE_SELINUX
        if (mac_selinux_use()) {
                r = setsockopt_int(s->native_fd, SOL_SOCKET, SO_PASSSEC, true);
                if (r < 0)
                        log_warning_errno(r, "SO_PASSSEC failed: %m");
        }
#endif

        r = setsockopt_int(s->native_fd, SOL_SOCKET, SO_TIMESTAMP, true);
        if (r < 0)
                return log_error_errno(r, "SO_TIMESTAMP failed: %m");

        r = sd_event_add_io(s->event, &s->native_event_source, s->native_fd, EPOLLIN, server_process_datagram, s);
        if (r < 0)
                return log_error_errno(r, "Failed to add native server fd to event loop: %m");

        r = sd_event_source_set_priority(s->native_event_source, SD_EVENT_PRIORITY_NORMAL+5);
        if (r < 0)
                return log_error_errno(r, "Failed to adjust native event source priority: %m");

        return 0;
}

Project: systemd
File: journald-native.c

static void server_process_entry_meta(
                const char *p, size_t l,
                const struct ucred *ucred,
                int *priority,
                char **identifier,
                char **message,
                pid_t *object_pid) {

        /* We need to determine the priority of this entry for the rate limiting logic */

        if (l == 10 &&
            startswith(p, "PRIORITY=") &&
            p[9] >= '0' && p[9] <= '9')
                *priority = (*priority & LOG_FACMASK) | (p[9] - '0');

        else if (l == 17 &&
                 startswith(p, "SYSLOG_FACILITY=") &&
                 p[16] >= '0' && p[16] <= '9')
                *priority = (*priority & LOG_PRIMASK) | ((p[16] - '0') << 3);

        else if (l == 18 &&
                 startswith(p, "SYSLOG_FACILITY=") &&
                 p[16] >= '0' && p[16] <= '9' &&
                 p[17] >= '0' && p[17] <= '9')
                *priority = (*priority & LOG_PRIMASK) | (((p[16] - '0')*10 + (p[17] - '0')) << 3);

        else if (l >= 19 &&
                 startswith(p, "SYSLOG_IDENTIFIER=")) {
                char *t;

                t = strndup(p + 18, l - 18);
                if (t) {
                        free(*identifier);
                        *identifier = t;
                }

        } else if (l >= 8 &&
                   startswith(p, "MESSAGE=")) {
                char *t;

                t = strndup(p + 8, l - 8);
                if (t) {
                        free(*message);
                        *message = t;
                }

        } else if (l > STRLEN("OBJECT_PID=") &&
                   l < STRLEN("OBJECT_PID=")  + DECIMAL_STR_MAX(pid_t) &&
                   startswith(p, "OBJECT_PID=") &&
                   allow_object_pid(ucred)) {
                char buf[DECIMAL_STR_MAX(pid_t)];
                memcpy(buf, p + STRLEN("OBJECT_PID="),
                       l - STRLEN("OBJECT_PID="));
                buf[l-STRLEN("OBJECT_PID=")] = '\0';

                (void) parse_pid(buf, object_pid);
        }
}

Project: systemd
File: journald-native.c

void server_process_native_message(
                Server *s,
                const char *buffer, size_t buffer_size,
                const struct ucred *ucred,
                const struct timeval *tv,
                const char *label, size_t label_len) {

        size_t remaining = buffer_size;
        ClientContext *context = NULL;
        int r;

        assert(s);
        assert(buffer || buffer_size == 0);

        if (ucred && pid_is_valid(ucred->pid)) {
                r = client_context_get(s, ucred->pid, ucred, label, label_len, NULL, &context);
                if (r < 0)
                        log_warning_errno(r, "Failed to retrieve credentials for PID " PID_FMT ", ignoring: %m", ucred->pid);
        }

        do {
                r = server_process_entry(s,
                                         (const uint8_t*) buffer + (buffer_size - remaining), &remaining,
                                         context, ucred, tv, label, label_len);
        } while (r == 0);
}