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dns: update detection of immutable resolv.conf

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Before, we would first check whether the file is immuable before
parsing main.rc-manager setting. That means, if you configured

  [main]
  dns=default
  rc-manager=unmanged

we would still first try to detect whether the file is immutable.
The result of course is only minor, e.g. showing up in logging
as rc-manager=immutable instead of rc-manager=unmanged.
Also, an immutable resolv.conf would suppress a warning about
a bogus rc-manager setting.

Also, when selecting rc-manager=symlink and resolv.conf is a symlink
to an immutable file, we don't actually care about that. The reason is,
that if the link-target is not /var/run/NetworkManager/resolv.conf,
we anyway wouldn't modify the file.

The effect of this change is pretty minor, now in logging you would see:
  dns-mgr: init: dns=default, rc-manager=symlink
  dns-mgr: update-resolv-conf: write internal file /var/run/NetworkManager/resolv.conf succeeded but don't update /etc/resolv.conf as it points to /some/where/else
instead of
  dns-mgr: init: dns=default, rc-manager=immutable
  dns-mgr: update-resolv-conf: write internal file /var/run/NetworkManager/resolv.conf succeeded

Which feels slightly more right.

Note that symlinks cannot have file attributes.

(cherry picked from commit 4711867915)
This commit is contained in:
Thomas Haller 2016-06-03 11:16:03 +02:00
parent 486fc0eade
commit 2826c7ad0f
1 changed files with 44 additions and 10 deletions
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54
src/dns-manager/nm-dns-manager.c
View file

@ -1508,19 +1508,53 @@ _clear_plugin (NMDnsManager *self)
return FALSE;
}
static bool
_get_resconf_immutable (void)
static NMDnsManagerResolvConfManager
_check_resconf_immutable (NMDnsManagerResolvConfManager rc_manager)
{
struct stat st;
int fd, flags;
bool immutable = FALSE;
fd = open (_PATH_RESCONF, O_RDONLY);
if (fd != -1) {
if (ioctl (fd, FS_IOC_GETFLAGS, &flags) != -1)
immutable = NM_FLAGS_HAS (flags, FS_IMMUTABLE_FL);
close (fd);
switch (rc_manager) {
case NM_DNS_MANAGER_RESOLV_CONF_MAN_UNKNOWN:
case NM_DNS_MANAGER_RESOLV_CONF_MAN_IMMUTABLE:
nm_assert_not_reached ();
/* fall-through */
case NM_DNS_MANAGER_RESOLV_CONF_MAN_UNMANAGED:
return NM_DNS_MANAGER_RESOLV_CONF_MAN_UNMANAGED;
default:
if (lstat (_PATH_RESCONF, &st) != 0)
return rc_manager;
if (S_ISLNK (st.st_mode)) {
/* only regular files and directories can have extended file attributes. */
switch (rc_manager) {
case NM_DNS_MANAGER_RESOLV_CONF_MAN_SYMLINK:
/* we don't care whether the link-target is immutable.
* If the symlink points to another file, rc-manager=symlink anyway backs off.
* Otherwise, we would only check whether our internal resolv.conf is immutable. */
return NM_DNS_MANAGER_RESOLV_CONF_MAN_SYMLINK;
case NM_DNS_MANAGER_RESOLV_CONF_MAN_UNKNOWN:
case NM_DNS_MANAGER_RESOLV_CONF_MAN_UNMANAGED:
case NM_DNS_MANAGER_RESOLV_CONF_MAN_IMMUTABLE:
nm_assert_not_reached ();
/* fall-through */
case NM_DNS_MANAGER_RESOLV_CONF_MAN_FILE:
case NM_DNS_MANAGER_RESOLV_CONF_MAN_RESOLVCONF:
case NM_DNS_MANAGER_RESOLV_CONF_MAN_NETCONFIG:
break;
}
}
fd = open (_PATH_RESCONF, O_RDONLY);
if (fd != -1) {
if (ioctl (fd, FS_IOC_GETFLAGS, &flags) != -1)
immutable = NM_FLAGS_HAS (flags, FS_IMMUTABLE_FL);
close (fd);
}
return immutable ? NM_DNS_MANAGER_RESOLV_CONF_MAN_IMMUTABLE : rc_manager;
}
return immutable;
}
NM_DEFINE_SINGLETON_GETTER (NMDnsManager, nm_dns_manager_get, NM_TYPE_DNS_MANAGER);
@ -1537,8 +1571,6 @@ init_resolv_conf_mode (NMDnsManager *self, gboolean force_reload_plugin)
if (nm_streq0 (mode, "none"))
rc_manager = NM_DNS_MANAGER_RESOLV_CONF_MAN_UNMANAGED;
else if (_get_resconf_immutable ())
rc_manager = NM_DNS_MANAGER_RESOLV_CONF_MAN_IMMUTABLE;
else {
const char *man;
@ -1570,6 +1602,8 @@ again:
}
}
rc_manager = _check_resconf_immutable (rc_manager);
if (nm_streq0 (mode, "dnsmasq")) {
if (force_reload_plugin || !NM_IS_DNS_DNSMASQ (priv->plugin)) {
_clear_plugin (self);