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resolv: Introduce struct resolv_conf with extended resolver state

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This change provides additional resolver configuration state which
is not exposed through the _res ABI.  It reuses the existing
initstamp field in the supposedly-private part of _res.  Some effort
is undertaken to avoid memory safety issues introduced by applications
which directly patch the _res object.

With this commit, only the initstamp field is moved into struct
resolv_conf.  Additional members will be added later, eventually
migrating the entire resolver configuration.
This commit is contained in:
Florian Weimer
2017-07-03 20:31:23 +02:00
parent 352f4ff9a2
commit f30a54b21b
9 changed files with 470 additions and 10 deletions
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38
resolv/resolv_context.c
View File

@@ -17,9 +17,11 @@
<http://www.gnu.org/licenses/>. */
#include <resolv_context.h>
#include <resolv_conf.h>
#include <resolv-internal.h>
#include <assert.h>
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
@@ -52,19 +54,37 @@ static __thread struct resolv_context *current attribute_tls_model_ie;
/* Initialize *RESP if RES_INIT is not yet set in RESP->options, or if
res_init in some other thread requested re-initializing. */
static __attribute__ ((warn_unused_result)) bool
maybe_init (struct __res_state *resp, bool preinit)
maybe_init (struct resolv_context *ctx, bool preinit)
{
struct __res_state *resp = ctx->resp;
if (resp->options & RES_INIT)
{
if (__res_initstamp != resp->_u._ext.initstamp)
/* If there is no associated resolv_conf object despite the
initialization, something modified *ctx->resp. Do not
override those changes. */
if (ctx->conf != NULL && ctx->conf->initstamp != __res_initstamp)
{
if (resp->nscount > 0)
/* This call will detach the extended resolver state. */
__res_iclose (resp, true);
return __res_vinit (resp, 1) == 0;
/* And this call will attach it again. */
if (__res_vinit (resp, 1) < 0)
{
/* The configuration no longer matches after failed
initialization. */
__resolv_conf_put (ctx->conf);
ctx->conf = NULL;
return false;
}
/* Delay the release of the old configuration until this
point, so that __res_vinit can reuse it if possible. */
__resolv_conf_put (ctx->conf);
ctx->conf = __resolv_conf_get (ctx->resp);
}
return true;
}
assert (ctx->conf == NULL);
if (preinit)
{
if (!resp->retrans)
@@ -75,7 +95,11 @@ maybe_init (struct __res_state *resp, bool preinit)
if (!resp->id)
resp->id = res_randomid ();
}
return __res_vinit (resp, preinit) == 0;
if (__res_vinit (resp, preinit) < 0)
return false;
ctx->conf = __resolv_conf_get (ctx->resp);
return true;
}
/* Allocate a new context object and initialize it. The object is put
@@ -87,6 +111,7 @@ context_alloc (struct __res_state *resp)
if (ctx == NULL)
return NULL;
ctx->resp = resp;
ctx->conf = __resolv_conf_get (resp);
ctx->__refcount = 1;
ctx->__from_res = true;
ctx->__next = current;
@@ -98,8 +123,11 @@ context_alloc (struct __res_state *resp)
static void
context_free (struct resolv_context *ctx)
{
int error_code = errno;
current = ctx->__next;
__resolv_conf_put (ctx->conf);
free (ctx);
__set_errno (error_code);
}
/* Reuse the current context object. */
@@ -130,7 +158,7 @@ context_get (bool preinit)
struct resolv_context *ctx = context_alloc (&_res);
if (ctx == NULL)
return NULL;
if (!maybe_init (ctx->resp, preinit))
if (!maybe_init (ctx, preinit))
{
context_free (ctx);
return NULL;