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Ignore fopen errors to use default values

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After 46bb820be3 `init_by_resolv_conf`
errors are no longer swallowed in `ares_init_options`. This has exposed
a previously unknown bug in `lookups` initialization code.

If there is no lookup configuration in `resolv.conf`,
`init_by_resolv_conf` will attempt to read it from other files available
on the system. However, some of these files may have restricted
permissions (like `600`), which will lead to `EACCESS` errno, which in
turn is handled like a fatal error by `init_by_resolv_conf`.

However, it sounds illogical that this error should be handled as a
fatal. There is a `init_by_defaults` call that overrides `lookups` with
default value, and certainly possible absence of lookup information is
the reason why this function exists in a first place!

I suggest handling any `fopen` errors as non-fatal ones, allowing to
pick up the `lookups` value from different config files, or to pick up
default value.
This commit is contained in:
Fedor Indutny
2016-02-10 18:00:51 -05:00
committed by David Drysdale
parent 87d641a907
commit e514088f96
1 changed files with 9 additions and 6 deletions
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15
ares_init.c
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@ -1315,15 +1315,16 @@ static int init_by_resolv_conf(ares_channel channel)
switch(error) {
case ENOENT:
case ESRCH:
status = ARES_EOF;
break;
default:
DEBUGF(fprintf(stderr, "fopen() failed with error: %d %s\n",
error, strerror(error)));
DEBUGF(fprintf(stderr, "Error opening file: %s\n",
"/etc/nsswitch.conf"));
status = ARES_EFILE;
}
/* ignore error, maybe we will get luck in next if clause */
status = ARES_EOF;
}
}
@ -1345,15 +1346,16 @@ static int init_by_resolv_conf(ares_channel channel)
switch(error) {
case ENOENT:
case ESRCH:
status = ARES_EOF;
break;
default:
DEBUGF(fprintf(stderr, "fopen() failed with error: %d %s\n",
error, strerror(error)));
DEBUGF(fprintf(stderr, "Error opening file: %s\n",
"/etc/host.conf"));
status = ARES_EFILE;
}
/* ignore error, maybe we will get luck in next if clause */
status = ARES_EOF;
}
}
@ -1375,14 +1377,15 @@ static int init_by_resolv_conf(ares_channel channel)
switch(error) {
case ENOENT:
case ESRCH:
status = ARES_EOF;
break;
default:
DEBUGF(fprintf(stderr, "fopen() failed with error: %d %s\n",
error, strerror(error)));
DEBUGF(fprintf(stderr, "Error opening file: %s\n", "/etc/svc.conf"));
status = ARES_EFILE;
}
/* ignore error, default value will be chosen for `channel->lookups` */
status = ARES_EOF;
}
}