Merge pull request #18896 from poettering/no-localhost-ipv6

if ipv6 is turned off, don't synthesize localhost as ::1 ever

src/basic/meson.build

@@ -235,6 +235,8 @@ basic_sources = files('''
         strv.h
         strxcpyx.c
         strxcpyx.h
+        sysctl-util.c
+        sysctl-util.h
         syslog-util.c
         syslog-util.h
         terminal-util.c

src/basic/socket-util.c

@@ -31,6 +31,7 @@
 #include "string-table.h"
 #include "string-util.h"
 #include "strv.h"
+#include "sysctl-util.h"
 #include "user-util.h"
 #include "utf8.h"
 
@@ -277,10 +278,48 @@ const char* socket_address_get_path(const SocketAddress *a) {
 }
 
 bool socket_ipv6_is_supported(void) {
-        if (access("/proc/net/if_inet6", F_OK) != 0)
+        static int cached = -1;
+
+        if (cached < 0) {
+
+                if (access("/proc/net/if_inet6", F_OK) < 0) {
+
+                        if (errno != ENOENT) {
+                                log_debug_errno(errno, "Unexpected error when checking whether /proc/net/if_inet6 exists: %m");
+                                return false;
+                        }
+
+                        cached = false;
+                } else
+                        cached = true;
+        }
+
+        return cached;
+}
+
+bool socket_ipv6_is_enabled(void) {
+        _cleanup_free_ char *v;
+        int r;
+
+        /* Much like socket_ipv6_is_supported(), but also checks that the sysctl that disables IPv6 on all
+         * interfaces isn't turned on */
+
+        if (!socket_ipv6_is_supported())
                 return false;
 
-        return true;
+        r = sysctl_read_ip_property(AF_INET6, "all", "disable_ipv6", &v);
+        if (r < 0) {
+                log_debug_errno(r, "Unexpected error reading 'net.ipv6.conf.all.disable_ipv6' sysctl: %m");
+                return true;
+        }
+
+        r = parse_boolean(v);
+        if (r < 0) {
+                log_debug_errno(r, "Failed to pare 'net.ipv6.conf.all.disable_ipv6' sysctl: %m");
+                return true;
+        }
+
+        return !r;
 }
 
 bool socket_address_matches_fd(const SocketAddress *a, int fd) {

src/basic/socket-util.h

@@ -101,6 +101,7 @@ bool socket_address_equal(const SocketAddress *a, const SocketAddress *b) _pure_
 const char* socket_address_get_path(const SocketAddress *a);
 
 bool socket_ipv6_is_supported(void);
+bool socket_ipv6_is_enabled(void);
 
 int sockaddr_port(const struct sockaddr *_sa, unsigned *port);
 const union in_addr_union *sockaddr_in_addr(const struct sockaddr *sa);

src/basic/sysctl-util.c

@@ -0,0 +1,130 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include "fd-util.h"
+#include "fileio.h"
+#include "log.h"
+#include "macro.h"
+#include "path-util.h"
+#include "string-util.h"
+#include "sysctl-util.h"
+
+char *sysctl_normalize(char *s) {
+        char *n;
+
+        n = strpbrk(s, "/.");
+
+        /* If the first separator is a slash, the path is
+         * assumed to be normalized and slashes remain slashes
+         * and dots remains dots. */
+
+        if (n && *n == '.')
+                /* Dots become slashes and slashes become dots. Fun. */
+                do {
+                        if (*n == '.')
+                                *n = '/';
+                        else
+                                *n = '.';
+
+                        n = strpbrk(n + 1, "/.");
+                } while (n);
+
+        path_simplify(s, true);
+
+        /* Kill the leading slash, but keep the first character of the string in the same place. */
+        if (*s == '/' && *(s+1))
+                memmove(s, s+1, strlen(s));
+
+        return s;
+}
+
+int sysctl_write(const char *property, const char *value) {
+        char *p;
+        _cleanup_close_ int fd = -1;
+
+        assert(property);
+        assert(value);
+
+        log_debug("Setting '%s' to '%.*s'.", property, (int) strcspn(value, NEWLINE), value);
+
+        p = strjoina("/proc/sys/", property);
+        fd = open(p, O_WRONLY|O_CLOEXEC);
+        if (fd < 0)
+                return -errno;
+
+        if (!endswith(value, "\n"))
+                value = strjoina(value, "\n");
+
+        if (write(fd, value, strlen(value)) < 0)
+                return -errno;
+
+        return 0;
+}
+
+int sysctl_writef(const char *property, const char *format, ...) {
+        _cleanup_free_ char *v = NULL;
+        va_list ap;
+        int r;
+
+        va_start(ap, format);
+        r = vasprintf(&v, format, ap);
+        va_end(ap);
+
+        if (r < 0)
+                return -ENOMEM;
+
+        return sysctl_write(property, v);
+}
+
+int sysctl_write_ip_property(int af, const char *ifname, const char *property, const char *value) {
+        const char *p;
+
+        assert(IN_SET(af, AF_INET, AF_INET6));
+        assert(property);
+        assert(value);
+
+        p = strjoina("/proc/sys/net/ipv", af == AF_INET ? "4" : "6",
+                     ifname ? "/conf/" : "", strempty(ifname),
+                     property[0] == '/' ? "" : "/", property);
+
+        log_debug("Setting '%s' to '%s'", p, value);
+
+        return write_string_file(p, value, WRITE_STRING_FILE_VERIFY_ON_FAILURE | WRITE_STRING_FILE_DISABLE_BUFFER);
+}
+
+int sysctl_read(const char *property, char **ret) {
+        char *p;
+
+        assert(property);
+        assert(ret);
+
+        p = strjoina("/proc/sys/", property);
+        return read_full_virtual_file(p, ret, NULL);
+}
+
+int sysctl_read_ip_property(int af, const char *ifname, const char *property, char **ret) {
+        _cleanup_free_ char *value = NULL;
+        const char *p;
+        int r;
+
+        assert(IN_SET(af, AF_INET, AF_INET6));
+        assert(property);
+
+        p = strjoina("/proc/sys/net/ipv", af == AF_INET ? "4" : "6",
+                     ifname ? "/conf/" : "", strempty(ifname),
+                     property[0] == '/' ? "" : "/", property);
+
+        r = read_full_virtual_file(p, &value, NULL);
+        if (r < 0)
+                return r;
+
+        truncate_nl(value);
+        if (ret)
+                *ret = TAKE_PTR(value);
+
+        return r;
+}

src/basic/sysctl-util.h

@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include "macro.h"
+#include "stdio-util.h"
+#include "string-util.h"
+
+char *sysctl_normalize(char *s);
+int sysctl_read(const char *property, char **value);
+int sysctl_write(const char *property, const char *value);
+int sysctl_writef(const char *property, const char *format, ...) _printf_(2, 3);
+
+int sysctl_read_ip_property(int af, const char *ifname, const char *property, char **ret);
+int sysctl_write_ip_property(int af, const char *ifname, const char *property, const char *value);
+static inline int sysctl_write_ip_property_boolean(int af, const char *ifname, const char *property, bool value) {
+        return sysctl_write_ip_property(af, ifname, property, one_zero(value));
+}
+
+#define DEFINE_SYSCTL_WRITE_IP_PROPERTY(name, type, format)           \
+        static inline int sysctl_write_ip_property_##name(int af, const char *ifname, const char *property, type value) { \
+                char buf[DECIMAL_STR_MAX(type)];                        \
+                xsprintf(buf, format, value);                           \
+                return sysctl_write_ip_property(af, ifname, property, buf); \
+        }
+
+DEFINE_SYSCTL_WRITE_IP_PROPERTY(int, int, "%i");
+DEFINE_SYSCTL_WRITE_IP_PROPERTY(uint32, uint32_t, "%" PRIu32);