-/* Copyright (C) 1993-2015 Free Software Foundation, Inc.
+/* Copyright (C) 1993-2022 Free Software Foundation, Inc.
This file is part of the GNU C Library.
- Contributed by David Mosberger (davidm@azstarnet.com).
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
- <http://www.gnu.org/licenses/>. */
+ <https://www.gnu.org/licenses/>. */
/* This file provides a Linux /etc/host.conf compatible front end to
the various name resolvers (/etc/hosts, named, NIS server, etc.).
Though mostly compatibly, the following differences exist compared
to the original implementation:
- - new command "spoof" takes an arguments like RESOLV_SPOOF_CHECK
- environment variable (i.e., `off', `nowarn', or `warn').
-
- line comments can appear anywhere (not just at the beginning of
a line)
*/
#include <sys/ioctl.h>
#include <unistd.h>
#include <netinet/in.h>
-#include <bits/libc-lock.h>
+#include <libc-lock.h>
#include "ifreq.h"
#include "res_hconf.h"
#include <wchar.h>
+#include <atomic.h>
#if IS_IN (libc)
# define fgets_unlocked __fgets_unlocked
/* Environment vars that all user to override default behavior: */
#define ENV_HOSTCONF "RESOLV_HOST_CONF"
-#define ENV_SPOOF "RESOLV_SPOOF_CHECK"
#define ENV_TRIM_OVERR "RESOLV_OVERRIDE_TRIM_DOMAINS"
#define ENV_TRIM_ADD "RESOLV_ADD_TRIM_DOMAINS"
#define ENV_MULTI "RESOLV_MULTI"
{
CB_none,
CB_arg_trimdomain_list,
- CB_arg_spoof,
CB_arg_bool
};
{
{"order", CB_none, 0},
{"trim", CB_arg_trimdomain_list, 0},
- {"spoof", CB_arg_spoof, 0},
{"multi", CB_arg_bool, HCONF_FLAG_MULTI},
- {"nospoof", CB_arg_bool, HCONF_FLAG_SPOOF},
- {"spoofalert", CB_arg_bool, HCONF_FLAG_SPOOFALERT},
{"reorder", CB_arg_bool, HCONF_FLAG_REORDER}
};
}
-static const char *
-arg_spoof (const char *fname, int line_num, const char *args)
-{
- const char *start = args;
- size_t len;
-
- args = skip_string (args);
- len = args - start;
-
- if (len == 3 && __strncasecmp (start, "off", len) == 0)
- _res_hconf.flags &= ~(HCONF_FLAG_SPOOF | HCONF_FLAG_SPOOFALERT);
- else
- {
- _res_hconf.flags |= (HCONF_FLAG_SPOOF | HCONF_FLAG_SPOOFALERT);
- if ((len == 6 && __strncasecmp (start, "nowarn", len) == 0)
- || !(len == 4 && __strncasecmp (start, "warn", len) == 0))
- _res_hconf.flags &= ~HCONF_FLAG_SPOOFALERT;
- }
- return args;
-}
-
-
static const char *
arg_bool (const char *fname, int line_num, const char *args, unsigned flag)
{
if (c->cb == CB_arg_trimdomain_list)
str = arg_trimdomain_list (fname, line_num, str);
- else if (c->cb == CB_arg_spoof)
- str = arg_spoof (fname, line_num, str);
else if (c->cb == CB_arg_bool)
str = arg_bool (fname, line_num, str, c->arg);
else
fclose (fp);
}
- envval = getenv (ENV_SPOOF);
- if (envval)
- arg_spoof (ENV_SPOOF, 1, envval);
-
envval = getenv (ENV_MULTI);
if (envval)
arg_bool (ENV_MULTI, 1, envval, HCONF_FLAG_MULTI);
arg_trimdomain_list (ENV_TRIM_OVERR, 1, envval);
}
- _res_hconf.initialized = 1;
+ /* See comments on the declaration of _res_hconf. */
+ atomic_store_release (&_res_hconf.initialized, 1);
}
{
struct
{
- u_int32_t addr;
- u_int32_t mask;
+ uint32_t addr;
+ uint32_t mask;
} ipv4;
} u;
} *ifaddrs);
{
#if defined SIOCGIFCONF && defined SIOCGIFNETMASK
int i, j;
- /* Number of interfaces. */
+ /* Number of interfaces. Also serves as a flag for the
+ double-checked locking idiom. */
static int num_ifs = -1;
- /* We need to protect the dynamic buffer handling. */
+ /* Local copy of num_ifs, for non-atomic access. */
+ int num_ifs_local;
+ /* We need to protect the dynamic buffer handling. The lock is only
+ acquired during initialization. Afterwards, a positive num_ifs
+ value indicates completed initialization. */
__libc_lock_define_initialized (static, lock);
/* Only reorder if we're supposed to. */
if (hp->h_addrtype != AF_INET)
return;
- if (num_ifs <= 0)
+ /* This load synchronizes with the release MO store in the
+ initialization block below. */
+ num_ifs_local = atomic_load_acquire (&num_ifs);
+ if (num_ifs_local <= 0)
{
struct ifreq *ifr, *cur_ifr;
int sd, num, i;
/* Initialize interface table. */
/* The SIOCGIFNETMASK ioctl will only work on an AF_INET socket. */
- sd = __socket (AF_INET, SOCK_DGRAM, 0);
+ sd = __socket (AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0);
if (sd < 0)
return;
/* Get lock. */
__libc_lock_lock (lock);
- /* Recheck, somebody else might have done the work by done. */
- if (num_ifs <= 0)
+ /* Recheck, somebody else might have done the work by now. No
+ ordering is required for the load because we have the lock,
+ and num_ifs is only updated under the lock. Also see (3) in
+ the analysis below. */
+ num_ifs_local = atomic_load_relaxed (&num_ifs);
+ if (num_ifs_local <= 0)
{
+ /* This is the only block which writes to num_ifs. It can
+ be executed several times (sequentially) if
+ initialization does not yield any interfaces, and num_ifs
+ remains zero. However, once we stored a positive value
+ in num_ifs below, this block cannot be entered again due
+ to the condition above. */
int new_num_ifs = 0;
/* Get a list of interfaces. */
for (cur_ifr = ifr, i = 0; i < num;
cur_ifr = __if_nextreq (cur_ifr), ++i)
{
+ union
+ {
+ struct sockaddr sa;
+ struct sockaddr_in sin;
+ } ss;
+
if (cur_ifr->ifr_addr.sa_family != AF_INET)
continue;
ifaddrs[new_num_ifs].addrtype = AF_INET;
- ifaddrs[new_num_ifs].u.ipv4.addr =
- ((struct sockaddr_in *) &cur_ifr->ifr_addr)->sin_addr.s_addr;
+ ss.sa = cur_ifr->ifr_addr;
+ ifaddrs[new_num_ifs].u.ipv4.addr = ss.sin.sin_addr.s_addr;
if (__ioctl (sd, SIOCGIFNETMASK, cur_ifr) < 0)
continue;
- ifaddrs[new_num_ifs].u.ipv4.mask =
- ((struct sockaddr_in *) &cur_ifr->ifr_netmask)->sin_addr.s_addr;
+ ss.sa = cur_ifr->ifr_netmask;
+ ifaddrs[new_num_ifs].u.ipv4.mask = ss.sin.sin_addr.s_addr;
/* Now we're committed to this entry. */
++new_num_ifs;
/* Release lock, preserve error value, and close socket. */
errno = save;
- num_ifs = new_num_ifs;
-
- __libc_lock_unlock (lock);
+ /* Advertise successful initialization if new_num_ifs is
+ positive (and no updates to ifaddrs are permitted after
+ that). Otherwise, num_ifs remains unchanged, at zero.
+ This store synchronizes with the initial acquire MO
+ load. */
+ atomic_store_release (&num_ifs, new_num_ifs);
+ /* Keep the local copy current, to save another load. */
+ num_ifs_local = new_num_ifs;
}
+ __libc_lock_unlock (lock);
+
__close (sd);
}
- if (num_ifs == 0)
+ /* num_ifs_local cannot be negative because the if statement above
+ covered this case. It can still be zero if we just performed
+ initialization, but could not find any interfaces. */
+ if (num_ifs_local == 0)
return;
+ /* The code below accesses ifaddrs, so we need to ensure that the
+ initialization happens-before this point.
+
+ The actual initialization is sequenced-before the release store
+ to num_ifs, and sequenced-before the end of the critical section.
+
+ This means there are three possible executions:
+
+ (1) The thread that initialized the data also uses it, so
+ sequenced-before is sufficient to ensure happens-before.
+
+ (2) The release MO store of num_ifs synchronizes-with the acquire
+ MO load, and the acquire MO load is sequenced before the use
+ of the initialized data below.
+
+ (3) We enter the critical section, and the relaxed MO load of
+ num_ifs yields a positive value. The write to ifaddrs is
+ sequenced-before leaving the critical section. Leaving the
+ critical section happens-before we entered the critical
+ section ourselves, which means that the write to ifaddrs
+ happens-before this point.
+
+ Consequently, all potential writes to ifaddrs (and the data it
+ points to) happens-before this point. */
+
/* Find an address for which we have a direct connection. */
for (i = 0; hp->h_addr_list[i]; ++i)
{
struct in_addr *haddr = (struct in_addr *) hp->h_addr_list[i];
- for (j = 0; j < num_ifs; ++j)
+ for (j = 0; j < num_ifs_local; ++j)
{
- u_int32_t if_addr = ifaddrs[j].u.ipv4.addr;
- u_int32_t if_netmask = ifaddrs[j].u.ipv4.mask;
+ uint32_t if_addr = ifaddrs[j].u.ipv4.addr;
+ uint32_t if_netmask = ifaddrs[j].u.ipv4.mask;
if (((haddr->s_addr ^ if_addr) & if_netmask) == 0)
{
projects / thirdparty / glibc.git / blobdiff