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nss-myhostname: resolve 'localhost' so that /etc/hosts becomes optional 

This makes sure nss-myhostname not only resolves the local host name to
127.0.0.2/::1 but also the host name 'localhost: to 127.0.0.1/::1. This
makes installation of /etc/passwd optional, as it usually only includes
a mapping for 'localhost'.

This change also resolves ::1 to the local hostname (as before), but
also lists 'localhost' as an alias. This means look-ups are now fully
reversible, even though they are 1:n mappings.

Finally, the module will no longer erroneously claim that local IP
addresses which aren't on the loopback device were.
This commit is contained in:
Lennart Poettering 2013-04-24 17:18:01 -03:00
parent 2b77f67e78
commit e8a7a31539
2 changed files with 136 additions and 56 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
TODO
View File

@ -26,6 +26,10 @@ Fedora 19:
Features:
* nss-myhostname: investigate whether there's any point in also
resolving localhost6, localhost.localdomain, ip6-localhost or any of
the other names often seen in /etc/hosts
* see if we can fix https://bugs.freedesktop.org/show_bug.cgi?id=63672
without dropping the location cache entirely.
@ -47,14 +51,10 @@ Features:
* timedatctl, localectl: possibly make some commands work without the daemon, for chroot situations...
* logind: consider making suspend inhibitor locks non-session specific, but keep suspend-key inhibitor locks session specific
* logind: add Suspend() bus calls which take timestamps to fix double suspend issues when somebody hits suspend and closes laptop quickly.
* we need dynamic units
* nss-myhostname should also resolve 'localhost' so that /etc/hosts becomes optional.
* add s.th. like "systemctl set-log-level debug"
* sd-login: allow enumerating machines and add inotify iface

184
src/nss-myhostname/nss-myhostname.c
View File

@ -32,7 +32,6 @@
#include "ifconf.h"
#include "macro.h"
#include "util.h"
/* Ensure that glibc's assert is used. We cannot use assert from macro.h, as
* libnss_myhostname will be linked into arbitrary programs which will, in turn
@ -101,31 +100,46 @@ enum nss_status _nss_myhostname_gethostbyname4_r(
unsigned lo_ifi;
char hn[HOST_NAME_MAX+1] = {};
const char *canonical = NULL;
size_t l, idx, ms;
char *r_name;
struct gaih_addrtuple *r_tuple, *r_tuple_prev = NULL;
struct address *addresses = NULL, *a;
unsigned n_addresses = 0, n;
uint32_t local_address_ipv4;
if (gethostname(hn, sizeof(hn)-1) < 0) {
*errnop = errno;
*h_errnop = NO_RECOVERY;
return NSS_STATUS_UNAVAIL;
if (strcasecmp(name, "localhost") == 0) {
/* We respond to 'localhost', so that /etc/hosts
* is optional */
canonical = "localhost";
local_address_ipv4 = htonl(INADDR_LOOPBACK);
} else {
/* We respond to our local host name */
if (gethostname(hn, sizeof(hn)-1) < 0) {
*errnop = errno;
*h_errnop = NO_RECOVERY;
return NSS_STATUS_UNAVAIL;
}
if (strcasecmp(name, hn) != 0) {
*errnop = ENOENT;
*h_errnop = HOST_NOT_FOUND;
return NSS_STATUS_NOTFOUND;
}
/* If this fails, n_addresses is 0. Which is fine */
ifconf_acquire_addresses(&addresses, &n_addresses);
canonical = hn;
local_address_ipv4 = LOCALADDRESS_IPV4;
}
if (strcasecmp(name, hn) != 0) {
*errnop = ENOENT;
*h_errnop = HOST_NOT_FOUND;
return NSS_STATUS_NOTFOUND;
}
/* If this fails, n_addresses is 0. Which is fine */
ifconf_acquire_addresses(&addresses, &n_addresses);
/* If this call fails we fill in 0 as scope. Which is fine */
lo_ifi = if_nametoindex(LOOPBACK_INTERFACE);
lo_ifi = n_addresses <= 0 ? if_nametoindex(LOOPBACK_INTERFACE) : 0;
l = strlen(hn);
l = strlen(canonical);
ms = ALIGN(l+1)+ALIGN(sizeof(struct gaih_addrtuple))*(n_addresses > 0 ? n_addresses : 2);
if (buflen < ms) {
*errnop = ENOMEM;
@ -136,7 +150,7 @@ enum nss_status _nss_myhostname_gethostbyname4_r(
/* First, fill in hostname */
r_name = buffer;
memcpy(r_name, hn, l+1);
memcpy(r_name, canonical, l+1);
idx = ALIGN(l+1);
if (n_addresses <= 0) {
@ -156,7 +170,7 @@ enum nss_status _nss_myhostname_gethostbyname4_r(
r_tuple->next = r_tuple_prev;
r_tuple->name = r_name;
r_tuple->family = AF_INET;
*(uint32_t*) r_tuple->addr = LOCALADDRESS_IPV4;
*(uint32_t*) r_tuple->addr = local_address_ipv4;
r_tuple->scopeid = (uint32_t) lo_ifi;
idx += ALIGN(sizeof(struct gaih_addrtuple));
@ -194,31 +208,34 @@ enum nss_status _nss_myhostname_gethostbyname4_r(
}
static enum nss_status fill_in_hostent(
const char *hn,
const char *canonical, const char *additional,
int af,
struct address *addresses, unsigned n_addresses,
uint32_t local_address_ipv4,
struct hostent *result,
char *buffer, size_t buflen,
int *errnop, int *h_errnop,
int32_t *ttlp,
char **canonp) {
size_t l, idx, ms;
char *r_addr, *r_name, *r_aliases, *r_addr_list;
size_t l_canonical, l_additional, idx, ms;
char *r_addr, *r_name, *r_aliases, *r_alias = NULL, *r_addr_list;
size_t alen;
struct address *addresses = NULL, *a;
unsigned n_addresses = 0, n, c;
struct address *a;
unsigned n, c;
alen = PROTO_ADDRESS_SIZE(af);
ifconf_acquire_addresses(&addresses, &n_addresses);
for (a = addresses, n = 0, c = 0; n < n_addresses; a++, n++)
if (af == a->family)
c++;
l = strlen(hn);
ms = ALIGN(l+1)+
l_canonical = strlen(canonical);
l_additional = additional ? strlen(additional) : 0;
ms = ALIGN(l_canonical+1)+
(additional ? ALIGN(l_additional+1) : 0) +
sizeof(char*)+
(additional ? sizeof(char*) : 0) +
(c > 0 ? c : 1)*ALIGN(alen)+
(c > 0 ? c+1 : 2)*sizeof(char*);
@ -229,15 +246,27 @@ static enum nss_status fill_in_hostent(
return NSS_STATUS_TRYAGAIN;
}
/* First, fill in hostname */
/* First, fill in hostnames */
r_name = buffer;
memcpy(r_name, hn, l+1);
idx = ALIGN(l+1);
memcpy(r_name, canonical, l_canonical+1);
idx = ALIGN(l_canonical+1);
/* Second, create (empty) aliases array */
if (additional) {
r_alias = buffer + idx;
memcpy(r_alias, additional, l_additional+1);
idx += ALIGN(l_additional+1);
}
/* Second, create aliases array */
r_aliases = buffer + idx;
*(char**) r_aliases = NULL;
idx += sizeof(char*);
if (additional) {
((char**) r_aliases)[0] = r_alias;
((char**) r_aliases)[1] = NULL;
idx += 2*sizeof(char*);
} else {
((char**) r_aliases)[0] = NULL;
idx += sizeof(char*);
}
/* Third, add addresses */
r_addr = buffer + idx;
@ -256,7 +285,7 @@ static enum nss_status fill_in_hostent(
idx += c*ALIGN(alen);
} else {
if (af == AF_INET)
*(uint32_t*) r_addr = LOCALADDRESS_IPV4;
*(uint32_t*) r_addr = local_address_ipv4;
else
memcpy(r_addr, LOCALADDRESS_IPV6, 16);
@ -316,6 +345,10 @@ enum nss_status _nss_myhostname_gethostbyname3_r(
char **canonp) {
char hn[HOST_NAME_MAX+1] = {};
struct address *addresses = NULL;
unsigned n_addresses = 0;
const char *canonical, *additional = NULL;
uint32_t local_address_ipv4;
if (af == AF_UNSPEC)
af = AF_INET;
@ -326,19 +359,39 @@ enum nss_status _nss_myhostname_gethostbyname3_r(
return NSS_STATUS_UNAVAIL;
}
if (gethostname(hn, sizeof(hn)-1) < 0) {
*errnop = errno;
*h_errnop = NO_RECOVERY;
return NSS_STATUS_UNAVAIL;
if (strcasecmp(name, "localhost") == 0) {
canonical = "localhost";
local_address_ipv4 = htonl(INADDR_LOOPBACK);
} else {
if (gethostname(hn, sizeof(hn)-1) < 0) {
*errnop = errno;
*h_errnop = NO_RECOVERY;
return NSS_STATUS_UNAVAIL;
}
if (strcasecmp(name, hn) != 0) {
*errnop = ENOENT;
*h_errnop = HOST_NOT_FOUND;
return NSS_STATUS_NOTFOUND;
}
ifconf_acquire_addresses(&addresses, &n_addresses);
canonical = hn;
additional = n_addresses <= 0 && af == AF_INET6 ? "localhost" : NULL;
local_address_ipv4 = LOCALADDRESS_IPV4;
}
if (strcasecmp(name, hn) != 0) {
*errnop = ENOENT;
*h_errnop = HOST_NOT_FOUND;
return NSS_STATUS_NOTFOUND;
}
return fill_in_hostent(hn, af, host, buffer, buflen, errnop, h_errnop, ttlp, canonp);
return fill_in_hostent(
canonical, additional,
af,
addresses, n_addresses,
local_address_ipv4,
host,
buffer, buflen,
errnop, h_errnop,
ttlp,
canonp);
}
enum nss_status _nss_myhostname_gethostbyname2_r(
@ -383,9 +436,11 @@ enum nss_status _nss_myhostname_gethostbyaddr2_r(
int32_t *ttlp) {
char hn[HOST_NAME_MAX+1] = {};
_cleanup_free_ struct address *addresses = NULL;
struct address *addresses = NULL;
struct address *a;
unsigned n_addresses = 0, n;
uint32_t local_address_ipv4 = LOCALADDRESS_IPV4;
const char *canonical = NULL, *additional = NULL;
if (len != PROTO_ADDRESS_SIZE(af)) {
*errnop = EINVAL;
@ -398,10 +453,18 @@ enum nss_status _nss_myhostname_gethostbyaddr2_r(
if ((*(uint32_t*) addr) == LOCALADDRESS_IPV4)
goto found;
if ((*(uint32_t*) addr) == htonl(INADDR_LOOPBACK)) {
canonical = "localhost";
local_address_ipv4 = htonl(INADDR_LOOPBACK);
goto found;
}
} else if (af == AF_INET6) {
if (memcmp(addr, LOCALADDRESS_IPV6, 16) == 0)
if (memcmp(addr, LOCALADDRESS_IPV6, 16) == 0) {
additional = "localhost";
goto found;
}
} else {
*errnop = EAFNOSUPPORT;
@ -422,17 +485,34 @@ enum nss_status _nss_myhostname_gethostbyaddr2_r(
*errnop = ENOENT;
*h_errnop = HOST_NOT_FOUND;
free(addresses);
return NSS_STATUS_NOTFOUND;
found:
if (gethostname(hn, sizeof(hn)-1) < 0) {
*errnop = errno;
*h_errnop = NO_RECOVERY;
if (!canonical) {
if (gethostname(hn, sizeof(hn)-1) < 0) {
*errnop = errno;
*h_errnop = NO_RECOVERY;
return NSS_STATUS_UNAVAIL;
free(addresses);
return NSS_STATUS_UNAVAIL;
}
canonical = hn;
}
return fill_in_hostent(hn, af, host, buffer, buflen, errnop, h_errnop, ttlp, NULL);
return fill_in_hostent(
canonical, additional,
af,
addresses, n_addresses,
local_address_ipv4,
host,
buffer, buflen,
errnop, h_errnop,
ttlp,
NULL);
}