niceSOFT/systemd: The systemd System and Service Manager

src/basic/hostname-util.c
330 строк10 KB
Lennart Poettering
hostname-util: don't allow machine tags to begin/end with '-' or '.'
01 июн 2026, 14:16
01 июн 2026, 14:1695c7dc3
/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include <stdlib.h>

#include "alloc-util.h"
#include "env-file.h"
#include "hostname-util.h"
#include "log.h"
#include "os-util.h"
#include "string-util.h"
#include "strv.h"
#include "user-util.h"

char* get_default_hostname_raw(void) {
        int r;

        /* Returns the default hostname, and leaves any ??? in place. */

        const char *e = secure_getenv("SYSTEMD_DEFAULT_HOSTNAME");
        if (e) {
                if (hostname_is_valid(e, VALID_HOSTNAME_QUESTION_MARK))
                        return strdup(e);

                log_debug("Invalid hostname in $SYSTEMD_DEFAULT_HOSTNAME, ignoring: %s", e);
        }

        _cleanup_free_ char *f = NULL;
        r = parse_os_release(NULL, "DEFAULT_HOSTNAME", &f);
        if (r < 0)
                log_debug_errno(r, "Failed to parse os-release, ignoring: %m");
        else if (f) {
                if (hostname_is_valid(f, VALID_HOSTNAME_QUESTION_MARK))
                        return TAKE_PTR(f);

                log_debug("Invalid hostname in os-release, ignoring: %s", f);
        }

        return strdup(FALLBACK_HOSTNAME);
}

bool valid_ldh_char(char c) {
        /* "LDH" → "Letters, digits, hyphens", as per RFC 5890, Section 2.3.1 */

        return ascii_isalpha(c) ||
                ascii_isdigit(c) ||
                c == '-';
}

bool hostname_is_valid(const char *s, ValidHostnameFlags flags) {
        unsigned n_dots = 0;
        const char *p;
        bool dot, hyphen;

        /* Check if s looks like a valid hostname or FQDN. This does not do full DNS validation, but only
         * checks if the name is composed of allowed characters and the length is not above the maximum
         * allowed by Linux (c.f. dns_name_is_valid()). A trailing dot is allowed if
         * VALID_HOSTNAME_TRAILING_DOT flag is set and at least two components are present in the name. Note
         * that due to the restricted charset and length this call is substantially more conservative than
         * dns_name_is_valid(). Doesn't accept empty hostnames, hostnames with leading dots, and hostnames
         * with multiple dots in a sequence. Doesn't allow hyphens at the beginning or end of label. */

        if (isempty(s))
                return false;

        if (streq(s, ".host")) /* Used by the container logic to denote the "root container" */
                return FLAGS_SET(flags, VALID_HOSTNAME_DOT_HOST);

        for (p = s, dot = hyphen = true; *p; p++)
                if (*p == '.') {
                        if (dot || hyphen)
                                return false;

                        dot = true;
                        hyphen = false;
                        n_dots++;

                } else if (*p == '-') {
                        if (dot)
                                return false;

                        dot = false;
                        hyphen = true;

                } else {
                        if (!valid_ldh_char(*p) && (*p != '?' || !FLAGS_SET(flags, VALID_HOSTNAME_QUESTION_MARK)))
                                return false;

                        dot = false;
                        hyphen = false;
                }

        if (dot && (n_dots < 2 || !FLAGS_SET(flags, VALID_HOSTNAME_TRAILING_DOT)))
                return false;
        if (hyphen)
                return false;

        /* Note that host name max is 64 on Linux, but DNS allows domain names up to 255 characters. */
        if (p - s > (ssize_t) LINUX_HOST_NAME_MAX)
                return false;

        return true;
}

char* hostname_cleanup(char *s) {
        char *p, *d;
        bool dot, hyphen;

        assert(s);

        for (p = s, d = s, dot = hyphen = true; *p && d - s < (ssize_t) LINUX_HOST_NAME_MAX; p++)
                if (*p == '.') {
                        if (dot || hyphen)
                                continue;

                        *(d++) = '.';
                        dot = true;
                        hyphen = false;

                } else if (*p == '-') {
                        if (dot)
                                continue;

                        *(d++) = '-';
                        dot = false;
                        hyphen = true;

                } else if (valid_ldh_char(*p) || *p == '?') {
                        *(d++) = *p;
                        dot = false;
                        hyphen = false;
                }

        if (d > s && IN_SET(d[-1], '-', '.'))
                /* The dot can occur at most once, but we might have multiple
                 * hyphens, hence the loop */
                d--;
        *d = 0;

        return s;
}

bool is_localhost(const char *hostname) {
        assert(hostname);

        /* This tries to identify local host and domain names
         * described in RFC6761 plus the redhatism of localdomain */

        return STRCASE_IN_SET(
                        hostname,
                        "localhost",
                        "localhost.",
                        "localhost.localdomain",
                        "localhost.localdomain.") ||
                endswith_no_case(hostname, ".localhost") ||
                endswith_no_case(hostname, ".localhost.") ||
                endswith_no_case(hostname, ".localhost.localdomain") ||
                endswith_no_case(hostname, ".localhost.localdomain.");
}

const char* etc_hostname(void) {
        static const char *cached = NULL;

        if (!cached)
                cached = secure_getenv("SYSTEMD_ETC_HOSTNAME") ?: "/etc/hostname";

        return cached;
}

const char* etc_machine_info(void) {
        static const char *cached = NULL;

        if (!cached)
                cached = secure_getenv("SYSTEMD_ETC_MACHINE_INFO") ?: "/etc/machine-info";

        return cached;
}

int get_pretty_hostname(char **ret) {
        _cleanup_free_ char *n = NULL;
        int r;

        assert(ret);

        r = parse_env_file(NULL, etc_machine_info(), "PRETTY_HOSTNAME", &n);
        if (r < 0)
                return r;

        if (isempty(n))
                return -ENXIO;

        *ret = TAKE_PTR(n);
        return 0;
}

int split_user_at_host(const char *s, char **ret_user, char **ret_host) {
        _cleanup_free_ char *u = NULL, *h = NULL;

        /* Splits a user@host expression (one of those we accept on --machine= and similar). Returns NULL in
         * each of the two return parameters if that part was left empty. */

        assert(s);

        const char *rhs = strchr(s, '@');
        if (rhs) {
                if (ret_user && rhs > s) {
                        u = strndup(s, rhs - s);
                        if (!u)
                                return -ENOMEM;
                }

                if (ret_host && rhs[1] != 0) {
                        h = strdup(rhs + 1);
                        if (!h)
                                return -ENOMEM;
                }

        } else {
                if (isempty(s))
                        return -EINVAL;

                if (ret_host) {
                        h = strdup(s);
                        if (!h)
                                return -ENOMEM;
                }
        }

        if (ret_user)
                *ret_user = TAKE_PTR(u);
        if (ret_host)
                *ret_host = TAKE_PTR(h);

        return !!rhs; /* return > 0 if '@' was specified, 0 otherwise */
}

int machine_spec_valid(const char *s) {
        _cleanup_free_ char *u = NULL, *h = NULL;
        int r;

        assert(s);

        r = split_user_at_host(s, &u, &h);
        if (r == -EINVAL)
                return false;
        if (r < 0)
                return r;

        if (u && !valid_user_group_name(u, VALID_USER_RELAX | VALID_USER_ALLOW_NUMERIC))
                return false;

        if (h && !hostname_is_valid(h, VALID_HOSTNAME_DOT_HOST))
                return false;

        return true;
}

bool machine_tag_is_valid(const char *s) {
        size_t n = strlen_ptr(s);
        if (n <= 0 || n >= 256)
                return false;

        /* Don't allow "-" and "." as first or last char. (This is load-bearing, we want that "+"/"-" can be
         * used as prefix for adding/removing tags from the list). */
        if (strchr("-.", s[0]) ||
            strchr("-.", s[n-1]))
                return false;

        return in_charset(s, ALPHANUMERICAL "-.");
}

bool machine_tag_list_is_valid(char **l) {
        size_t n = 0;
        STRV_FOREACH(i, l) {
                n++;
                if (n > MACHINE_TAGS_MAX)
                        return false;

                if (!machine_tag_is_valid(*i))
                        return false;
        }

        return true;
}

int machine_tags_from_string(const char *s, bool graceful, char ***ret) {
        int r;

        assert(ret);

        /* Parses the colon-separated TAGS= machine-info field into a sorted, deduplicated strv. Each tag is
         * validated: if 'graceful' is true invalid tags are silently dropped, otherwise an invalid tag makes
         * us fail with -EINVAL. The result is NULL if no (valid) tags remain. */

        if (isempty(s)) {
                *ret = NULL;
                return 0;
        }

        _cleanup_strv_free_ char **l = strv_split(s, ":");
        if (!l)
                return -ENOMEM;

        strv_sort_uniq(l);

        if (!graceful) {
                if (!machine_tag_list_is_valid(l))
                        return -EINVAL;

                *ret = strv_isempty(l) ? NULL : TAKE_PTR(l);
                return 0;
        }

        size_t n = 0;
        _cleanup_strv_free_ char **cleaned = NULL;
        STRV_FOREACH(i, l) {
                if (!machine_tag_is_valid(*i))
                        continue;

                n++;
                if (n > MACHINE_TAGS_MAX)
                        return -E2BIG;

                r = strv_extend(&cleaned, *i);
                if (r < 0)
                        return r;
        }

        *ret = TAKE_PTR(cleaned);
        return 0;
}