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glibc/resolv/resolv_conf.c
Carlos O'Donell 2827ab990a libc: Extend __libc_freeres framework (Bug 23329). 
The __libc_freeres framework does not extend to non-libc.so objects.
This causes problems in general for valgrind and mtrace detecting
unfreed objects in both libdl.so and libpthread.so.  This change is
a pre-requisite to properly moving the malloc hooks out of malloc
since such a move now requires precise accounting of all allocated
data before destructors are run.

This commit adds a proper hook in libc.so.6 for both libdl.so and
for libpthread.so, this ensures that shm-directory.c which uses
freeit () to free memory is called properly.  We also remove the
nptl_freeres hook and fall back to using weak-ref-and-check idiom
for a loaded libpthread.so, thus making this process similar for
all DSOs.

Lastly we follow best practice and use explicit free calls for
both libdl.so and libpthread.so instead of the generic hook process
which has undefined order.

Tested on x86_64 with no regressions.

Signed-off-by: DJ Delorie <dj@redhat.com>
Signed-off-by: Carlos O'Donell <carlos@redhat.com>
2018-06-29 22:39:06 -04:00

701 lines
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/* Extended resolver state separate from struct __res_state.
Copyright (C) 2017-2018 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
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/>. */
#include <resolv_conf.h>
#include <alloc_buffer.h>
#include <assert.h>
#include <libc-lock.h>
#include <resolv-internal.h>
#include <sys/stat.h>
#include <libc-symbols.h>
/* _res._u._ext.__glibc_extension_index is used as an index into a
struct resolv_conf_array object. The intent of this construction
is to make reasonably sure that even if struct __res_state objects
are copied around and patched by applications, we can still detect
accesses to stale extended resolver state. The array elements are
either struct resolv_conf * pointers (if the LSB is cleared) or
free list entries (if the LSB is set). The free list is used to
speed up finding available entries in the array. */
#define DYNARRAY_STRUCT resolv_conf_array
#define DYNARRAY_ELEMENT uintptr_t
#define DYNARRAY_PREFIX resolv_conf_array_
#define DYNARRAY_INITIAL_SIZE 0
#include <malloc/dynarray-skeleton.c>
/* A magic constant for XORing the extension index
(_res._u._ext.__glibc_extension_index). This makes it less likely
that a valid index is created by accident. In particular, a zero
value leads to an invalid index. */
#define INDEX_MAGIC 0x26a8fa5e48af8061ULL
/* Global resolv.conf-related state. */
struct resolv_conf_global
{
/* struct __res_state objects contain the extension index
(_res._u._ext.__glibc_extension_index ^ INDEX_MAGIC), which
refers to an element of this array. When a struct resolv_conf
object (extended resolver state) is associated with a struct
__res_state object (legacy resolver state), its reference count
is increased and added to this array. Conversely, if the
extended state is detached from the basic state (during
reinitialization or deallocation), the index is decremented, and
the array element is overwritten with NULL. */
struct resolv_conf_array array;
/* Start of the free list in the array. Zero if the free list is
empty. Otherwise, free_list_start >> 1 is the first element of
the free list (and the free list entries all have their LSB set
and are shifted one to the left). */
uintptr_t free_list_start;
/* Cached current configuration object for /etc/resolv.conf. */
struct resolv_conf *conf_current;
/* These properties of /etc/resolv.conf are used to check if the
configuration needs reloading. */
struct timespec conf_mtime;
struct timespec conf_ctime;
off64_t conf_size;
ino64_t conf_ino;
};
/* Lazily allocated storage for struct resolv_conf_global. */
static struct resolv_conf_global *global;
/* The lock synchronizes access to global and *global. It also
protects the __refcount member of struct resolv_conf. */
__libc_lock_define_initialized (static, lock);
/* Ensure that GLOBAL is allocated and lock it. Return NULL if
memory allocation failes. */
static struct resolv_conf_global *
get_locked_global (void)
{
__libc_lock_lock (lock);
/* Use relaxed MO through because of load outside the lock in
__resolv_conf_detach. */
struct resolv_conf_global *global_copy = atomic_load_relaxed (&global);
if (global_copy == NULL)
{
global_copy = calloc (1, sizeof (*global));
if (global_copy == NULL)
return NULL;
atomic_store_relaxed (&global, global_copy);
resolv_conf_array_init (&global_copy->array);
}
return global_copy;
}
/* Relinquish the lock acquired by get_locked_global. */
static void
put_locked_global (struct resolv_conf_global *global_copy)
{
__libc_lock_unlock (lock);
}
/* Decrement the reference counter. The caller must acquire the lock
around the function call. */
static void
conf_decrement (struct resolv_conf *conf)
{
assert (conf->__refcount > 0);
if (--conf->__refcount == 0)
free (conf);
}
struct resolv_conf *
__resolv_conf_get_current (void)
{
struct stat64 st;
if (stat64 (_PATH_RESCONF, &st) != 0)
{
switch (errno)
{
case EACCES:
case EISDIR:
case ELOOP:
case ENOENT:
case ENOTDIR:
case EPERM:
/* Ignore errors due to file system contents. */
memset (&st, 0, sizeof (st));
break;
default:
/* Other errors are fatal. */
return NULL;
}
}
struct resolv_conf_global *global_copy = get_locked_global ();
if (global_copy == NULL)
return NULL;
struct resolv_conf *conf;
if (global_copy->conf_current != NULL
&& (global_copy->conf_mtime.tv_sec == st.st_mtim.tv_sec
&& global_copy->conf_mtime.tv_nsec == st.st_mtim.tv_nsec
&& global_copy->conf_ctime.tv_sec == st.st_ctim.tv_sec
&& global_copy->conf_ctime.tv_nsec == st.st_ctim.tv_nsec
&& global_copy->conf_ino == st.st_ino
&& global_copy->conf_size == st.st_size))
/* We can reuse the cached configuration object. */
conf = global_copy->conf_current;
else
{
/* Parse configuration while holding the lock. This avoids
duplicate work. */
conf = __resolv_conf_load (NULL);
if (conf != NULL)
{
if (global_copy->conf_current != NULL)
conf_decrement (global_copy->conf_current);
global_copy->conf_current = conf; /* Takes ownership. */
/* Update file modification stamps. The configuration we
read could be a newer version of the file, but this does
not matter because this will lead to an extraneous reload
later. */
global_copy->conf_mtime = st.st_mtim;
global_copy->conf_ctime = st.st_ctim;
global_copy->conf_ino = st.st_ino;
global_copy->conf_size = st.st_size;
}
}
if (conf != NULL)
{
/* Return an additional reference. */
assert (conf->__refcount > 0);
++conf->__refcount;
assert (conf->__refcount > 0);
}
put_locked_global (global_copy);
return conf;
}
/* Internal implementation of __resolv_conf_get, without validation
against *RESP. */
static struct resolv_conf *
resolv_conf_get_1 (const struct __res_state *resp)
{
/* Not initialized, and therefore no assoicated context. */
if (!(resp->options & RES_INIT))
return NULL;
struct resolv_conf_global *global_copy = get_locked_global ();
if (global_copy == NULL)
/* A memory allocation failure here means that no associated
contexts exists, so returning NULL is correct. */
return NULL;
size_t index = resp->_u._ext.__glibc_extension_index ^ INDEX_MAGIC;
struct resolv_conf *conf = NULL;
if (index < resolv_conf_array_size (&global_copy->array))
{
uintptr_t *slot = resolv_conf_array_at (&global_copy->array, index);
if (!(*slot & 1))
{
conf = (struct resolv_conf *) *slot;
assert (conf->__refcount > 0);
++conf->__refcount;
}
}
put_locked_global (global_copy);
return conf;
}
/* Return true if both IPv4 addresses are equal. */
static bool
same_address_v4 (const struct sockaddr_in *left,
const struct sockaddr_in *right)
{
return left->sin_addr.s_addr == right->sin_addr.s_addr
&& left->sin_port == right->sin_port;
}
/* Return true if both IPv6 addresses are equal. This ignores the
flow label. */
static bool
same_address_v6 (const struct sockaddr_in6 *left,
const struct sockaddr_in6 *right)
{
return memcmp (&left->sin6_addr, &right->sin6_addr,
sizeof (left->sin6_addr)) == 0
&& left->sin6_port == right->sin6_port
&& left->sin6_scope_id == right->sin6_scope_id;
}
static bool
same_address (const struct sockaddr *left, const struct sockaddr *right)
{
if (left->sa_family != right->sa_family)
return false;
switch (left->sa_family)
{
case AF_INET:
return same_address_v4 ((const struct sockaddr_in *) left,
(const struct sockaddr_in *) right);
case AF_INET6:
return same_address_v6 ((const struct sockaddr_in6 *) left,
(const struct sockaddr_in6 *) right);
}
return false;
}
/* Check that *RESP and CONF match. Used by __resolv_conf_get. */
static bool
resolv_conf_matches (const struct __res_state *resp,
const struct resolv_conf *conf)
{
/* NB: Do not compare the options, retrans, retry, ndots. These can
be changed by applicaiton. */
/* Check that the name servers in *RESP have not been modified by
the application. */
{
size_t nserv = conf->nameserver_list_size;
if (nserv > MAXNS)
nserv = MAXNS;
/* _ext.nscount is 0 until initialized by res_send.c. */
if (resp->nscount != nserv
|| (resp->_u._ext.nscount != 0 && resp->_u._ext.nscount != nserv))
return false;
for (size_t i = 0; i < nserv; ++i)
{
if (resp->nsaddr_list[i].sin_family == 0)
{
if (resp->_u._ext.nsaddrs[i]->sin6_family != AF_INET6)
return false;
if (!same_address ((struct sockaddr *) resp->_u._ext.nsaddrs[i],
conf->nameserver_list[i]))
return false;
}
else if (resp->nsaddr_list[i].sin_family != AF_INET)
return false;
else if (!same_address ((struct sockaddr *) &resp->nsaddr_list[i],
conf->nameserver_list[i]))
return false;
}
}
/* Check that the search list in *RESP has not been modified by the
application. */
{
if (resp->dnsrch[0] == NULL)
{
/* Empty search list. No default domain name. */
return conf->search_list_size == 0 && resp->defdname[0] == '\0';
}
if (resp->dnsrch[0] != resp->defdname)
/* If the search list is not empty, it must start with the
default domain name. */
return false;
size_t nsearch;
for (nsearch = 0; nsearch < MAXDNSRCH; ++nsearch)
if (resp->dnsrch[nsearch] == NULL)
break;
if (nsearch > MAXDNSRCH)
/* Search list is not null-terminated. */
return false;
size_t search_list_size = 0;
for (size_t i = 0; i < conf->search_list_size; ++i)
{
if (resp->dnsrch[i] != NULL)
{
search_list_size += strlen (resp->dnsrch[i]) + 1;
if (strcmp (resp->dnsrch[i], conf->search_list[i]) != 0)
return false;
}
else
{
/* resp->dnsrch is truncated if the number of elements
exceeds MAXDNSRCH, or if the combined storage space for
the search list exceeds what can be stored in
resp->defdname. */
if (i == MAXDNSRCH || search_list_size > sizeof (resp->dnsrch))
break;
/* Otherwise, a mismatch indicates a match failure. */
return false;
}
}
}
/* Check that the sort list has not been modified. */
{
size_t nsort = conf->sort_list_size;
if (nsort > MAXRESOLVSORT)
nsort = MAXRESOLVSORT;
if (resp->nsort != nsort)
return false;
for (size_t i = 0; i < nsort; ++i)
if (resp->sort_list[i].addr.s_addr != conf->sort_list[i].addr.s_addr
|| resp->sort_list[i].mask != conf->sort_list[i].mask)
return false;
}
return true;
}
struct resolv_conf *
__resolv_conf_get (struct __res_state *resp)
{
struct resolv_conf *conf = resolv_conf_get_1 (resp);
if (conf == NULL)
return NULL;
if (resolv_conf_matches (resp, conf))
return conf;
__resolv_conf_put (conf);
return NULL;
}
void
__resolv_conf_put (struct resolv_conf *conf)
{
if (conf == NULL)
return;
__libc_lock_lock (lock);
conf_decrement (conf);
__libc_lock_unlock (lock);
}
struct resolv_conf *
__resolv_conf_allocate (const struct resolv_conf *init)
{
/* Allocate in decreasing order of alignment. */
_Static_assert (__alignof__ (const char *const *)
<= __alignof__ (struct resolv_conf), "alignment");
_Static_assert (__alignof__ (struct sockaddr_in6)
<= __alignof__ (const char *const *), "alignment");
_Static_assert (__alignof__ (struct sockaddr_in)
== __alignof__ (struct sockaddr_in6), "alignment");
_Static_assert (__alignof__ (struct resolv_sortlist_entry)
<= __alignof__ (struct sockaddr_in), "alignment");
/* Space needed by the nameserver addresses. */
size_t address_space = 0;
for (size_t i = 0; i < init->nameserver_list_size; ++i)
if (init->nameserver_list[i]->sa_family == AF_INET)
address_space += sizeof (struct sockaddr_in);
else
{
assert (init->nameserver_list[i]->sa_family == AF_INET6);
address_space += sizeof (struct sockaddr_in6);
}
/* Space needed by the search list strings. */
size_t string_space = 0;
for (size_t i = 0; i < init->search_list_size; ++i)
string_space += strlen (init->search_list[i]) + 1;
/* Allocate the buffer. */
void *ptr;
struct alloc_buffer buffer = alloc_buffer_allocate
(sizeof (struct resolv_conf)
+ init->nameserver_list_size * sizeof (init->nameserver_list[0])
+ address_space
+ init->search_list_size * sizeof (init->search_list[0])
+ init->sort_list_size * sizeof (init->sort_list[0])
+ string_space,
&ptr);
struct resolv_conf *conf
= alloc_buffer_alloc (&buffer, struct resolv_conf);
if (conf == NULL)
/* Memory allocation failure. */
return NULL;
assert (conf == ptr);
/* Initialize the contents. */
conf->__refcount = 1;
conf->retrans = init->retrans;
conf->retry = init->retry;
conf->options = init->options;
conf->ndots = init->ndots;
/* Allocate the arrays with pointers. These must come first because
they have the highets alignment. */
conf->nameserver_list_size = init->nameserver_list_size;
const struct sockaddr **nameserver_array = alloc_buffer_alloc_array
(&buffer, const struct sockaddr *, init->nameserver_list_size);
conf->nameserver_list = nameserver_array;
conf->search_list_size = init->search_list_size;
const char **search_array = alloc_buffer_alloc_array
(&buffer, const char *, init->search_list_size);
conf->search_list = search_array;
/* Fill the name server list array. */
for (size_t i = 0; i < init->nameserver_list_size; ++i)
if (init->nameserver_list[i]->sa_family == AF_INET)
{
struct sockaddr_in *sa = alloc_buffer_alloc
(&buffer, struct sockaddr_in);
*sa = *(struct sockaddr_in *) init->nameserver_list[i];
nameserver_array[i] = (struct sockaddr *) sa;
}
else
{
struct sockaddr_in6 *sa = alloc_buffer_alloc
(&buffer, struct sockaddr_in6);
*sa = *(struct sockaddr_in6 *) init->nameserver_list[i];
nameserver_array[i] = (struct sockaddr *) sa;
}
/* Allocate and fill the sort list array. */
{
conf->sort_list_size = init->sort_list_size;
struct resolv_sortlist_entry *array = alloc_buffer_alloc_array
(&buffer, struct resolv_sortlist_entry, init->sort_list_size);
conf->sort_list = array;
for (size_t i = 0; i < init->sort_list_size; ++i)
array[i] = init->sort_list[i];
}
/* Fill the search list array. This must come last because the
strings are the least aligned part of the allocation. */
{
for (size_t i = 0; i < init->search_list_size; ++i)
search_array[i] = alloc_buffer_copy_string
(&buffer, init->search_list[i]);
}
assert (!alloc_buffer_has_failed (&buffer));
return conf;
}
/* Update *RESP from the extended state. */
static __attribute__ ((nonnull (1, 2), warn_unused_result)) bool
update_from_conf (struct __res_state *resp, const struct resolv_conf *conf)
{
resp->defdname[0] = '\0';
resp->pfcode = 0;
resp->_vcsock = -1;
resp->_flags = 0;
resp->ipv6_unavail = false;
resp->__glibc_unused_qhook = NULL;
resp->__glibc_unused_rhook = NULL;
resp->retrans = conf->retrans;
resp->retry = conf->retry;
resp->options = conf->options;
resp->ndots = conf->ndots;
/* Copy the name server addresses. */
{
resp->nscount = 0;
resp->_u._ext.nscount = 0;
size_t nserv = conf->nameserver_list_size;
if (nserv > MAXNS)
nserv = MAXNS;
for (size_t i = 0; i < nserv; i++)
{
if (conf->nameserver_list[i]->sa_family == AF_INET)
{
resp->nsaddr_list[i]
= *(struct sockaddr_in *)conf->nameserver_list[i];
resp->_u._ext.nsaddrs[i] = NULL;
}
else
{
assert (conf->nameserver_list[i]->sa_family == AF_INET6);
resp->nsaddr_list[i].sin_family = 0;
/* Make a defensive copy of the name server address, in
case the application overwrites it. */
struct sockaddr_in6 *sa = malloc (sizeof (*sa));
if (sa == NULL)
{
for (size_t j = 0; j < i; ++j)
free (resp->_u._ext.nsaddrs[j]);
return false;
}
*sa = *(struct sockaddr_in6 *)conf->nameserver_list[i];
resp->_u._ext.nsaddrs[i] = sa;
}
resp->_u._ext.nssocks[i] = -1;
}
resp->nscount = nserv;
/* Leave resp->_u._ext.nscount at 0. res_send.c handles this. */
}
/* Fill in the prefix of the search list. It is truncated either at
MAXDNSRCH, or if reps->defdname has insufficient space. */
{
struct alloc_buffer buffer
= alloc_buffer_create (resp->defdname, sizeof (resp->defdname));
size_t size = conf->search_list_size;
size_t i;
for (i = 0; i < size && i < MAXDNSRCH; ++i)
{
resp->dnsrch[i] = alloc_buffer_copy_string
(&buffer, conf->search_list[i]);
if (resp->dnsrch[i] == NULL)
/* No more space in resp->defdname. Truncate. */
break;
}
resp->dnsrch[i] = NULL;
}
/* Copy the sort list. */
{
size_t nsort = conf->sort_list_size;
if (nsort > MAXRESOLVSORT)
nsort = MAXRESOLVSORT;
for (size_t i = 0; i < nsort; ++i)
{
resp->sort_list[i].addr = conf->sort_list[i].addr;
resp->sort_list[i].mask = conf->sort_list[i].mask;
}
resp->nsort = nsort;
}
/* The overlapping parts of both configurations should agree after
initialization. */
assert (resolv_conf_matches (resp, conf));
return true;
}
/* Decrement the configuration object at INDEX and free it if the
reference counter reaches 0. *GLOBAL_COPY must be locked and
remains so. */
static void
decrement_at_index (struct resolv_conf_global *global_copy, size_t index)
{
if (index < resolv_conf_array_size (&global_copy->array))
{
/* Index found. */
uintptr_t *slot = resolv_conf_array_at (&global_copy->array, index);
/* Check that the slot is not already part of the free list. */
if (!(*slot & 1))
{
struct resolv_conf *conf = (struct resolv_conf *) *slot;
conf_decrement (conf);
/* Put the slot onto the free list. */
*slot = global_copy->free_list_start;
global_copy->free_list_start = (index << 1) | 1;
}
}
}
bool
__resolv_conf_attach (struct __res_state *resp, struct resolv_conf *conf)
{
assert (conf->__refcount > 0);
struct resolv_conf_global *global_copy = get_locked_global ();
if (global_copy == NULL)
return false;
/* Try to find an unused index in the array. */
size_t index;
{
if (global_copy->free_list_start & 1)
{
/* Unlink from the free list. */
index = global_copy->free_list_start >> 1;
uintptr_t *slot = resolv_conf_array_at (&global_copy->array, index);
global_copy->free_list_start = *slot;
assert (global_copy->free_list_start == 0
|| global_copy->free_list_start & 1);
/* Install the configuration pointer. */
*slot = (uintptr_t) conf;
}
else
{
size_t size = resolv_conf_array_size (&global_copy->array);
/* No usable index found. Increase the array size. */
resolv_conf_array_add (&global_copy->array, (uintptr_t) conf);
if (resolv_conf_array_has_failed (&global_copy->array))
{
put_locked_global (global_copy);
__set_errno (ENOMEM);
return false;
}
/* The new array element was added at the end. */
index = size;
}
}
/* We have added a new reference to the object. */
++conf->__refcount;
assert (conf->__refcount > 0);
put_locked_global (global_copy);
if (!update_from_conf (resp, conf))
{
/* Drop the reference we acquired. Reacquire the lock. The
object has already been allocated, so it cannot be NULL this
time. */
global_copy = get_locked_global ();
decrement_at_index (global_copy, index);
put_locked_global (global_copy);
return false;
}
resp->_u._ext.__glibc_extension_index = index ^ INDEX_MAGIC;
return true;
}
void
__resolv_conf_detach (struct __res_state *resp)
{
if (atomic_load_relaxed (&global) == NULL)
/* Detach operation after a shutdown, or without any prior
attachment. We cannot free the data (and there might not be
anything to free anyway). */
return;
struct resolv_conf_global *global_copy = get_locked_global ();
size_t index = resp->_u._ext.__glibc_extension_index ^ INDEX_MAGIC;
decrement_at_index (global_copy, index);
/* Clear the index field, so that accidental reuse is less
likely. */
resp->_u._ext.__glibc_extension_index = 0;
put_locked_global (global_copy);
}
/* Deallocate the global data. */
libc_freeres_fn (freeres)
{
/* No locking because this function is supposed to be called when
the process has turned single-threaded. */
if (global == NULL)
return;
if (global->conf_current != NULL)
{
conf_decrement (global->conf_current);
global->conf_current = NULL;
}
/* Note that this frees only the array itself. The pointed-to
configuration objects should have been deallocated by res_nclose
and per-thread cleanup functions. */
resolv_conf_array_free (&global->array);
free (global);
/* Stop potential future __resolv_conf_detach calls from accessing
deallocated memory. */
global = NULL;
}
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