21 Dec
2015
21 Dec
'15
6:34 p.m.
Implement simplest variant of /etc/gai.conf to control getaddrinfo
IPv6/IPv4 addresses sorting. Keep the default sort order - IPv6 first,
IPv4 second. To invert it, just create /etc/gai.conf containing single line:
precedence ::ffff:0:0/96 100
Example before:
$ nslookup security.debian.org 8.8.8.8
Server: 8.8.8.8
Address 1: 8.8.8.8 google-public-dns-a.google.com
Name: security.debian.org
Address 1: 2001:a78:5:0:216:35ff:fe7f:be4f villa.debian.org
Address 2: 2001:a78:5:1:216:35ff:fe7f:6ceb lobos.debian.org
Address 3: 195.20.242.89 wieck.debian.org
Address 4: 212.211.132.250 lobos.debian.org
Address 5: 212.211.132.32 villa.debian.org
After patch & precedence set in /etc/gai.conf:
$ nslookup security.debian.org 8.8.8.8
Server: 8.8.8.8
Address 1: 8.8.8.8 google-public-dns-a.google.com
Name: security.debian.org
Address 1: 195.20.242.89 wieck.debian.org
Address 2: 212.211.132.250 lobos.debian.org
Address 3: 212.211.132.32 villa.debian.org
Address 4: 2001:a78:5:0:216:35ff:fe7f:be4f villa.debian.org
Address 5: 2001:a78:5:1:216:35ff:fe7f:6ceb lobos.debian.org
bloat-o-meter report:
function old new delta
getaddrinfo 726 1138 +412
gaih_inet 2660 2692 +32
.rodata 16618 16643 +25
__gai_precedence - 1 +1
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 4/0 up/down: 882/0) Total: 470 bytes
Signed-off-by: Leonid Lisovskiy <lly.dev(a)gmail.com>
diff --git a/libc/inet/getaddrinfo.c b/libc/inet/getaddrinfo.c
--- a/libc/inet/getaddrinfo.c
+++ b/libc/inet/getaddrinfo.c
@@ -62,6 +62,7 @@
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
+#include <stdbool.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netinet/in.h>
@@ -70,6 +71,7 @@
#include <sys/utsname.h>
#include <net/if.h>
#include <ifaddrs.h>
+#include "internal/parse_config.h"
#define GAIH_OKIFUNSPEC 0x0100
#define GAIH_EAI ~(GAIH_OKIFUNSPEC)
@@ -348,6 +350,11 @@ gaih_inet_serv(const char *servicename, const
struct gaih_typeproto *tp,
return 0;
}
+#if defined __UCLIBC_HAS_IPV6__
+static uint8_t __gai_precedence = 0; /* =1 - IPv6, IPv4
+ =2 - IPv4, IPv6 */
+#endif
+
/* NB: also uses h,pat,rc,no_data variables */
#define gethosts(_family, _type) \
{ \
@@ -552,21 +559,32 @@ gaih_inet(const char *name, const struct
gaih_service *service,
if (at->family == AF_UNSPEC && !(req->ai_flags &
AI_NUMERICHOST)) {
struct hostent *h;
struct gaih_addrtuple **pat = &at;
- int no_data = 0;
- int no_inet6_data;
+ int no_data, no_inet6_data;
+#if defined __UCLIBC_HAS_IPV6__
+ bool first_try = true;
+#endif
/*
* If we are looking for both IPv4 and IPv6 address we don't want
* the lookup functions to automatically promote IPv4 addresses to
* IPv6 addresses.
*/
+ no_inet6_data = no_data = 0;
#if defined __UCLIBC_HAS_IPV6__
+ if (__gai_precedence == 2)
+ goto try_v4;
+
+ try_v6:
if (req->ai_family == AF_UNSPEC || req->ai_family == AF_INET6)
if (!(req->ai_flags & AI_ADDRCONFIG) || (seen & SEEN_IPV6))
gethosts(AF_INET6, struct in6_addr);
-#endif
no_inet6_data = no_data;
+ if (!first_try)
+ goto tried_all;
+ first_try = false;
+ try_v4:
+#endif
if (req->ai_family == AF_INET
|| (!v4mapped && req->ai_family == AF_UNSPEC)
|| (v4mapped && (no_inet6_data != 0 || (req->ai_flags &
AI_ALL)))
@@ -574,7 +592,14 @@ gaih_inet(const char *name, const struct
gaih_service *service,
if (!(req->ai_flags & AI_ADDRCONFIG) || (seen & SEEN_IPV4))
gethosts(AF_INET, struct in_addr);
}
+#if defined __UCLIBC_HAS_IPV6__
+ if (first_try) {
+ first_try = false;
+ goto try_v6;
+ }
+ tried_all:
+#endif
if (no_data != 0 && no_inet6_data != 0) {
/* If both requests timed out report this. */
if (no_data == EAI_AGAIN && no_inet6_data == EAI_AGAIN)
@@ -775,6 +800,71 @@ static const struct gaih gaih[] = {
{ PF_UNSPEC, NULL }
};
+#if defined __UCLIBC_HAS_IPV6__
+
+/*
+ * A call to getaddrinfo might return multiple answers. To provide
+ * possibility to change the sorting we must use /etc/gai.conf file,
+ * like glibc.
+ *
+ * gai.conf format:
+ *
+ * label <netmask> <precedence>
+ * The value is added to the label table used in
+ * the RFC 3484 sorting. If any label definition
+ * is present in the configuration file is present,
+ * the default table is not used. All the label
+ * definitions of the default table which are to
+ * be maintained have to be duplicated.
+ * precedence <netmask> <precedence>
+ * This keyword is similar to label, but instead
+ * the value is added to the precedence table as
+ * specified in RFC 3484. Once again, the presence
+ * of a single precedence line in the configuration
+ * file causes the default table to not be used.
+ *
+ * The simplified uclibc's implementation allows to change the IPv4/IPv6
+ * sorting order for a whole address space only, i.e
+ * "precedence ::ffff:0:0/96 100" is only supported.
+ */
+static void __gai_conf_parse(void)
+{
+ /* NO reread of /etc/gai.conf on change. */
+ if (__gai_precedence != 0)
+ return;
+
+ __gai_precedence = 1; /* default IPv6 */
+
+ parser_t *parser;
+ char **tok = NULL;
+
+ parser = config_open("/etc/gai.conf");
+ if (!parser)
+ return;
+
+ while (config_read(parser, &tok, 3, 3, "# \t", PARSE_NORMAL)) {
+ if (strcmp(tok[0], "precedence") == 0) {
+ char *pfx;
+ struct in6_addr mask;
+
+ pfx = strchr(tok[1], '/');
+ if (!pfx)
+ continue;
+ *(pfx++) = 0;
+ if (inet_pton(AF_INET6, tok[1], &mask) <= 0)
+ continue;
+ if (IN6_IS_ADDR_V4MAPPED(&mask)
+ && mask.s6_addr32[3] == 0
+ && atoi(pfx) == 96 && atoi(tok[2]) == 100)
+ __gai_precedence = 2; /* IPv4 first */
+ }
+ }
+ config_close(parser);
+}
+#else
+# define __gai_conf_parse(x)
+#endif /* __UCLIBC_HAS_IPV6__ */
+
void
freeaddrinfo(struct addrinfo *ai)
{
@@ -834,6 +923,7 @@ getaddrinfo(const char *name, const char *service,
} else
pservice = NULL;
+ __gai_conf_parse();
g = gaih;
pg = NULL;
p = NULL;
--